Index: projects/clang1000-import/contrib/llvm-project/lld/ELF/LinkerScript.cpp
===================================================================
--- projects/clang1000-import/contrib/llvm-project/lld/ELF/LinkerScript.cpp	(revision 357258)
+++ projects/clang1000-import/contrib/llvm-project/lld/ELF/LinkerScript.cpp	(revision 357259)
@@ -1,1205 +1,1214 @@
 //===- LinkerScript.cpp ---------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file contains the parser/evaluator of the linker script.
 //
 //===----------------------------------------------------------------------===//
 
 #include "LinkerScript.h"
 #include "Config.h"
 #include "InputSection.h"
 #include "OutputSections.h"
 #include "SymbolTable.h"
 #include "Symbols.h"
 #include "SyntheticSections.h"
 #include "Target.h"
 #include "Writer.h"
 #include "lld/Common/Memory.h"
 #include "lld/Common/Strings.h"
 #include "lld/Common/Threads.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/BinaryFormat/ELF.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 #include <algorithm>
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
 #include <iterator>
 #include <limits>
 #include <string>
 #include <vector>
 
 using namespace llvm;
 using namespace llvm::ELF;
 using namespace llvm::object;
 using namespace llvm::support::endian;
 
 namespace lld {
 namespace elf {
 LinkerScript *script;
 
 static uint64_t getOutputSectionVA(SectionBase *sec) {
   OutputSection *os = sec->getOutputSection();
   assert(os && "input section has no output section assigned");
   return os ? os->addr : 0;
 }
 
 uint64_t ExprValue::getValue() const {
   if (sec)
     return alignTo(sec->getOffset(val) + getOutputSectionVA(sec),
                    alignment);
   return alignTo(val, alignment);
 }
 
 uint64_t ExprValue::getSecAddr() const {
   if (sec)
     return sec->getOffset(0) + getOutputSectionVA(sec);
   return 0;
 }
 
 uint64_t ExprValue::getSectionOffset() const {
   // If the alignment is trivial, we don't have to compute the full
   // value to know the offset. This allows this function to succeed in
   // cases where the output section is not yet known.
   if (alignment == 1 && !sec)
     return val;
   return getValue() - getSecAddr();
 }
 
 OutputSection *LinkerScript::createOutputSection(StringRef name,
                                                  StringRef location) {
   OutputSection *&secRef = nameToOutputSection[name];
   OutputSection *sec;
   if (secRef && secRef->location.empty()) {
     // There was a forward reference.
     sec = secRef;
   } else {
     sec = make<OutputSection>(name, SHT_PROGBITS, 0);
     if (!secRef)
       secRef = sec;
   }
   sec->location = location;
   return sec;
 }
 
 OutputSection *LinkerScript::getOrCreateOutputSection(StringRef name) {
   OutputSection *&cmdRef = nameToOutputSection[name];
   if (!cmdRef)
     cmdRef = make<OutputSection>(name, SHT_PROGBITS, 0);
   return cmdRef;
 }
 
 // Expands the memory region by the specified size.
 static void expandMemoryRegion(MemoryRegion *memRegion, uint64_t size,
                                StringRef regionName, StringRef secName) {
   memRegion->curPos += size;
   uint64_t newSize = memRegion->curPos - memRegion->origin;
   if (newSize > memRegion->length)
     error("section '" + secName + "' will not fit in region '" + regionName +
           "': overflowed by " + Twine(newSize - memRegion->length) + " bytes");
 }
 
 void LinkerScript::expandMemoryRegions(uint64_t size) {
   if (ctx->memRegion)
     expandMemoryRegion(ctx->memRegion, size, ctx->memRegion->name,
                        ctx->outSec->name);
   // Only expand the LMARegion if it is different from memRegion.
   if (ctx->lmaRegion && ctx->memRegion != ctx->lmaRegion)
     expandMemoryRegion(ctx->lmaRegion, size, ctx->lmaRegion->name,
                        ctx->outSec->name);
 }
 
 void LinkerScript::expandOutputSection(uint64_t size) {
   ctx->outSec->size += size;
   expandMemoryRegions(size);
 }
 
 void LinkerScript::setDot(Expr e, const Twine &loc, bool inSec) {
   uint64_t val = e().getValue();
   if (val < dot && inSec)
     error(loc + ": unable to move location counter backward for: " +
           ctx->outSec->name);
 
   // Update to location counter means update to section size.
   if (inSec)
     expandOutputSection(val - dot);
 
   dot = val;
 }
 
 // Used for handling linker symbol assignments, for both finalizing
 // their values and doing early declarations. Returns true if symbol
 // should be defined from linker script.
 static bool shouldDefineSym(SymbolAssignment *cmd) {
   if (cmd->name == ".")
     return false;
 
   if (!cmd->provide)
     return true;
 
   // If a symbol was in PROVIDE(), we need to define it only
   // when it is a referenced undefined symbol.
   Symbol *b = symtab->find(cmd->name);
   if (b && !b->isDefined())
     return true;
   return false;
 }
 
 // Called by processSymbolAssignments() to assign definitions to
 // linker-script-defined symbols.
 void LinkerScript::addSymbol(SymbolAssignment *cmd) {
   if (!shouldDefineSym(cmd))
     return;
 
   // Define a symbol.
   ExprValue value = cmd->expression();
   SectionBase *sec = value.isAbsolute() ? nullptr : value.sec;
   uint8_t visibility = cmd->hidden ? STV_HIDDEN : STV_DEFAULT;
 
   // When this function is called, section addresses have not been
   // fixed yet. So, we may or may not know the value of the RHS
   // expression.
   //
   // For example, if an expression is `x = 42`, we know x is always 42.
   // However, if an expression is `x = .`, there's no way to know its
   // value at the moment.
   //
   // We want to set symbol values early if we can. This allows us to
   // use symbols as variables in linker scripts. Doing so allows us to
   // write expressions like this: `alignment = 16; . = ALIGN(., alignment)`.
   uint64_t symValue = value.sec ? 0 : value.getValue();
 
   Defined newSym(nullptr, cmd->name, STB_GLOBAL, visibility, STT_NOTYPE,
                  symValue, 0, sec);
 
   Symbol *sym = symtab->insert(cmd->name);
   sym->mergeProperties(newSym);
   sym->replace(newSym);
   cmd->sym = cast<Defined>(sym);
 }
 
 // This function is called from LinkerScript::declareSymbols.
 // It creates a placeholder symbol if needed.
 static void declareSymbol(SymbolAssignment *cmd) {
   if (!shouldDefineSym(cmd))
     return;
 
   uint8_t visibility = cmd->hidden ? STV_HIDDEN : STV_DEFAULT;
   Defined newSym(nullptr, cmd->name, STB_GLOBAL, visibility, STT_NOTYPE, 0, 0,
                  nullptr);
 
   // We can't calculate final value right now.
   Symbol *sym = symtab->insert(cmd->name);
   sym->mergeProperties(newSym);
   sym->replace(newSym);
 
   cmd->sym = cast<Defined>(sym);
   cmd->provide = false;
   sym->scriptDefined = true;
 }
 
 using SymbolAssignmentMap =
     DenseMap<const Defined *, std::pair<SectionBase *, uint64_t>>;
 
 // Collect section/value pairs of linker-script-defined symbols. This is used to
 // check whether symbol values converge.
 static SymbolAssignmentMap
 getSymbolAssignmentValues(const std::vector<BaseCommand *> &sectionCommands) {
   SymbolAssignmentMap ret;
   for (BaseCommand *base : sectionCommands) {
     if (auto *cmd = dyn_cast<SymbolAssignment>(base)) {
       if (cmd->sym) // sym is nullptr for dot.
         ret.try_emplace(cmd->sym,
                         std::make_pair(cmd->sym->section, cmd->sym->value));
       continue;
     }
     for (BaseCommand *sub_base : cast<OutputSection>(base)->sectionCommands)
       if (auto *cmd = dyn_cast<SymbolAssignment>(sub_base))
         if (cmd->sym)
           ret.try_emplace(cmd->sym,
                           std::make_pair(cmd->sym->section, cmd->sym->value));
   }
   return ret;
 }
 
 // Returns the lexicographical smallest (for determinism) Defined whose
 // section/value has changed.
 static const Defined *
 getChangedSymbolAssignment(const SymbolAssignmentMap &oldValues) {
   const Defined *changed = nullptr;
   for (auto &it : oldValues) {
     const Defined *sym = it.first;
     if (std::make_pair(sym->section, sym->value) != it.second &&
         (!changed || sym->getName() < changed->getName()))
       changed = sym;
   }
   return changed;
 }
 
 // This method is used to handle INSERT AFTER statement. Here we rebuild
 // the list of script commands to mix sections inserted into.
 void LinkerScript::processInsertCommands() {
   std::vector<BaseCommand *> v;
   auto insert = [&](std::vector<BaseCommand *> &from) {
     v.insert(v.end(), from.begin(), from.end());
     from.clear();
   };
 
   for (BaseCommand *base : sectionCommands) {
     if (auto *os = dyn_cast<OutputSection>(base)) {
       insert(insertBeforeCommands[os->name]);
       v.push_back(base);
       insert(insertAfterCommands[os->name]);
       continue;
     }
     v.push_back(base);
   }
 
   for (auto &cmds : {insertBeforeCommands, insertAfterCommands})
     for (const std::pair<StringRef, std::vector<BaseCommand *>> &p : cmds)
       if (!p.second.empty())
         error("unable to INSERT AFTER/BEFORE " + p.first +
               ": section not defined");
 
   sectionCommands = std::move(v);
 }
 
 // Symbols defined in script should not be inlined by LTO. At the same time
 // we don't know their final values until late stages of link. Here we scan
 // over symbol assignment commands and create placeholder symbols if needed.
 void LinkerScript::declareSymbols() {
   assert(!ctx);
   for (BaseCommand *base : sectionCommands) {
     if (auto *cmd = dyn_cast<SymbolAssignment>(base)) {
       declareSymbol(cmd);
       continue;
     }
 
     // If the output section directive has constraints,
     // we can't say for sure if it is going to be included or not.
     // Skip such sections for now. Improve the checks if we ever
     // need symbols from that sections to be declared early.
     auto *sec = cast<OutputSection>(base);
     if (sec->constraint != ConstraintKind::NoConstraint)
       continue;
     for (BaseCommand *base2 : sec->sectionCommands)
       if (auto *cmd = dyn_cast<SymbolAssignment>(base2))
         declareSymbol(cmd);
   }
 }
 
 // This function is called from assignAddresses, while we are
 // fixing the output section addresses. This function is supposed
 // to set the final value for a given symbol assignment.
 void LinkerScript::assignSymbol(SymbolAssignment *cmd, bool inSec) {
   if (cmd->name == ".") {
     setDot(cmd->expression, cmd->location, inSec);
     return;
   }
 
   if (!cmd->sym)
     return;
 
   ExprValue v = cmd->expression();
   if (v.isAbsolute()) {
     cmd->sym->section = nullptr;
     cmd->sym->value = v.getValue();
   } else {
     cmd->sym->section = v.sec;
     cmd->sym->value = v.getSectionOffset();
   }
 }
 
 static std::string getFilename(InputFile *file) {
   if (!file)
     return "";
   if (file->archiveName.empty())
     return file->getName();
   return (file->archiveName + "(" + file->getName() + ")").str();
 }
 
 bool LinkerScript::shouldKeep(InputSectionBase *s) {
   if (keptSections.empty())
     return false;
   std::string filename = getFilename(s->file);
   for (InputSectionDescription *id : keptSections)
     if (id->filePat.match(filename))
       for (SectionPattern &p : id->sectionPatterns)
         if (p.sectionPat.match(s->name))
           return true;
   return false;
 }
 
 // A helper function for the SORT() command.
 static bool matchConstraints(ArrayRef<InputSectionBase *> sections,
                              ConstraintKind kind) {
   if (kind == ConstraintKind::NoConstraint)
     return true;
 
   bool isRW = llvm::any_of(
       sections, [](InputSectionBase *sec) { return sec->flags & SHF_WRITE; });
 
   return (isRW && kind == ConstraintKind::ReadWrite) ||
          (!isRW && kind == ConstraintKind::ReadOnly);
 }
 
 static void sortSections(MutableArrayRef<InputSectionBase *> vec,
                          SortSectionPolicy k) {
   auto alignmentComparator = [](InputSectionBase *a, InputSectionBase *b) {
     // ">" is not a mistake. Sections with larger alignments are placed
     // before sections with smaller alignments in order to reduce the
     // amount of padding necessary. This is compatible with GNU.
     return a->alignment > b->alignment;
   };
   auto nameComparator = [](InputSectionBase *a, InputSectionBase *b) {
     return a->name < b->name;
   };
   auto priorityComparator = [](InputSectionBase *a, InputSectionBase *b) {
     return getPriority(a->name) < getPriority(b->name);
   };
 
   switch (k) {
   case SortSectionPolicy::Default:
   case SortSectionPolicy::None:
     return;
   case SortSectionPolicy::Alignment:
     return llvm::stable_sort(vec, alignmentComparator);
   case SortSectionPolicy::Name:
     return llvm::stable_sort(vec, nameComparator);
   case SortSectionPolicy::Priority:
     return llvm::stable_sort(vec, priorityComparator);
   }
 }
 
 // Sort sections as instructed by SORT-family commands and --sort-section
 // option. Because SORT-family commands can be nested at most two depth
 // (e.g. SORT_BY_NAME(SORT_BY_ALIGNMENT(.text.*))) and because the command
 // line option is respected even if a SORT command is given, the exact
 // behavior we have here is a bit complicated. Here are the rules.
 //
 // 1. If two SORT commands are given, --sort-section is ignored.
 // 2. If one SORT command is given, and if it is not SORT_NONE,
 //    --sort-section is handled as an inner SORT command.
 // 3. If one SORT command is given, and if it is SORT_NONE, don't sort.
 // 4. If no SORT command is given, sort according to --sort-section.
 static void sortInputSections(MutableArrayRef<InputSectionBase *> vec,
                               const SectionPattern &pat) {
   if (pat.sortOuter == SortSectionPolicy::None)
     return;
 
   if (pat.sortInner == SortSectionPolicy::Default)
     sortSections(vec, config->sortSection);
   else
     sortSections(vec, pat.sortInner);
   sortSections(vec, pat.sortOuter);
 }
 
 // Compute and remember which sections the InputSectionDescription matches.
 std::vector<InputSectionBase *>
 LinkerScript::computeInputSections(const InputSectionDescription *cmd) {
   std::vector<InputSectionBase *> ret;
 
   // Collects all sections that satisfy constraints of Cmd.
   for (const SectionPattern &pat : cmd->sectionPatterns) {
     size_t sizeBefore = ret.size();
 
     for (InputSectionBase *sec : inputSections) {
       if (!sec->isLive() || sec->parent)
         continue;
 
       // For -emit-relocs we have to ignore entries like
       //   .rela.dyn : { *(.rela.data) }
       // which are common because they are in the default bfd script.
       // We do not ignore SHT_REL[A] linker-synthesized sections here because
       // want to support scripts that do custom layout for them.
       if (isa<InputSection>(sec) &&
           cast<InputSection>(sec)->getRelocatedSection())
         continue;
 
       std::string filename = getFilename(sec->file);
       if (!cmd->filePat.match(filename) ||
           pat.excludedFilePat.match(filename) ||
           !pat.sectionPat.match(sec->name))
         continue;
 
       ret.push_back(sec);
     }
 
     sortInputSections(
         MutableArrayRef<InputSectionBase *>(ret).slice(sizeBefore), pat);
   }
   return ret;
 }
 
 void LinkerScript::discard(InputSectionBase *s) {
   if (s == in.shStrTab || s == mainPart->relrDyn)
     error("discarding " + s->name + " section is not allowed");
 
   // You can discard .hash and .gnu.hash sections by linker scripts. Since
   // they are synthesized sections, we need to handle them differently than
   // other regular sections.
   if (s == mainPart->gnuHashTab)
     mainPart->gnuHashTab = nullptr;
   if (s == mainPart->hashTab)
     mainPart->hashTab = nullptr;
 
   s->markDead();
   s->parent = nullptr;
   for (InputSection *ds : s->dependentSections)
     discard(ds);
 }
 
 std::vector<InputSectionBase *>
 LinkerScript::createInputSectionList(OutputSection &outCmd) {
   std::vector<InputSectionBase *> ret;
 
   for (BaseCommand *base : outCmd.sectionCommands) {
     if (auto *cmd = dyn_cast<InputSectionDescription>(base)) {
       cmd->sectionBases = computeInputSections(cmd);
       for (InputSectionBase *s : cmd->sectionBases)
         s->parent = &outCmd;
       ret.insert(ret.end(), cmd->sectionBases.begin(), cmd->sectionBases.end());
     }
   }
   return ret;
 }
 
 // Create output sections described by SECTIONS commands.
 void LinkerScript::processSectionCommands() {
   size_t i = 0;
   for (BaseCommand *base : sectionCommands) {
     if (auto *sec = dyn_cast<OutputSection>(base)) {
       std::vector<InputSectionBase *> v = createInputSectionList(*sec);
 
       // The output section name `/DISCARD/' is special.
       // Any input section assigned to it is discarded.
       if (sec->name == "/DISCARD/") {
         for (InputSectionBase *s : v)
           discard(s);
         sec->sectionCommands.clear();
         continue;
       }
 
       // This is for ONLY_IF_RO and ONLY_IF_RW. An output section directive
       // ".foo : ONLY_IF_R[OW] { ... }" is handled only if all member input
       // sections satisfy a given constraint. If not, a directive is handled
       // as if it wasn't present from the beginning.
       //
       // Because we'll iterate over SectionCommands many more times, the easy
       // way to "make it as if it wasn't present" is to make it empty.
       if (!matchConstraints(v, sec->constraint)) {
         for (InputSectionBase *s : v)
           s->parent = nullptr;
         sec->sectionCommands.clear();
         continue;
       }
 
       // Handle subalign (e.g. ".foo : SUBALIGN(32) { ... }"). If subalign
       // is given, input sections are aligned to that value, whether the
       // given value is larger or smaller than the original section alignment.
       if (sec->subalignExpr) {
         uint32_t subalign = sec->subalignExpr().getValue();
         for (InputSectionBase *s : v)
           s->alignment = subalign;
       }
 
       // Set the partition field the same way OutputSection::recordSection()
       // does. Partitions cannot be used with the SECTIONS command, so this is
       // always 1.
       sec->partition = 1;
 
       sec->sectionIndex = i++;
     }
   }
 }
 
 void LinkerScript::processSymbolAssignments() {
   // Dot outside an output section still represents a relative address, whose
   // sh_shndx should not be SHN_UNDEF or SHN_ABS. Create a dummy aether section
   // that fills the void outside a section. It has an index of one, which is
   // indistinguishable from any other regular section index.
   aether = make<OutputSection>("", 0, SHF_ALLOC);
   aether->sectionIndex = 1;
 
   // ctx captures the local AddressState and makes it accessible deliberately.
   // This is needed as there are some cases where we cannot just thread the
   // current state through to a lambda function created by the script parser.
   AddressState state;
   ctx = &state;
   ctx->outSec = aether;
 
   for (BaseCommand *base : sectionCommands) {
     if (auto *cmd = dyn_cast<SymbolAssignment>(base))
       addSymbol(cmd);
     else
       for (BaseCommand *sub_base : cast<OutputSection>(base)->sectionCommands)
         if (auto *cmd = dyn_cast<SymbolAssignment>(sub_base))
           addSymbol(cmd);
   }
 
   ctx = nullptr;
 }
 
 static OutputSection *findByName(ArrayRef<BaseCommand *> vec,
                                  StringRef name) {
   for (BaseCommand *base : vec)
     if (auto *sec = dyn_cast<OutputSection>(base))
       if (sec->name == name)
         return sec;
   return nullptr;
 }
 
 static OutputSection *createSection(InputSectionBase *isec,
                                     StringRef outsecName) {
   OutputSection *sec = script->createOutputSection(outsecName, "<internal>");
   sec->recordSection(isec);
   return sec;
 }
 
 static OutputSection *
 addInputSec(StringMap<TinyPtrVector<OutputSection *>> &map,
             InputSectionBase *isec, StringRef outsecName) {
   // Sections with SHT_GROUP or SHF_GROUP attributes reach here only when the -r
   // option is given. A section with SHT_GROUP defines a "section group", and
   // its members have SHF_GROUP attribute. Usually these flags have already been
   // stripped by InputFiles.cpp as section groups are processed and uniquified.
   // However, for the -r option, we want to pass through all section groups
   // as-is because adding/removing members or merging them with other groups
   // change their semantics.
   if (isec->type == SHT_GROUP || (isec->flags & SHF_GROUP))
     return createSection(isec, outsecName);
 
   // Imagine .zed : { *(.foo) *(.bar) } script. Both foo and bar may have
   // relocation sections .rela.foo and .rela.bar for example. Most tools do
   // not allow multiple REL[A] sections for output section. Hence we
   // should combine these relocation sections into single output.
   // We skip synthetic sections because it can be .rela.dyn/.rela.plt or any
   // other REL[A] sections created by linker itself.
   if (!isa<SyntheticSection>(isec) &&
       (isec->type == SHT_REL || isec->type == SHT_RELA)) {
     auto *sec = cast<InputSection>(isec);
     OutputSection *out = sec->getRelocatedSection()->getOutputSection();
 
     if (out->relocationSection) {
       out->relocationSection->recordSection(sec);
       return nullptr;
     }
 
     out->relocationSection = createSection(isec, outsecName);
     return out->relocationSection;
   }
 
   //  The ELF spec just says
   // ----------------------------------------------------------------
   // In the first phase, input sections that match in name, type and
   // attribute flags should be concatenated into single sections.
   // ----------------------------------------------------------------
   //
   // However, it is clear that at least some flags have to be ignored for
   // section merging. At the very least SHF_GROUP and SHF_COMPRESSED have to be
   // ignored. We should not have two output .text sections just because one was
   // in a group and another was not for example.
   //
   // It also seems that wording was a late addition and didn't get the
   // necessary scrutiny.
   //
   // Merging sections with different flags is expected by some users. One
   // reason is that if one file has
   //
   // int *const bar __attribute__((section(".foo"))) = (int *)0;
   //
   // gcc with -fPIC will produce a read only .foo section. But if another
   // file has
   //
   // int zed;
   // int *const bar __attribute__((section(".foo"))) = (int *)&zed;
   //
   // gcc with -fPIC will produce a read write section.
   //
   // Last but not least, when using linker script the merge rules are forced by
   // the script. Unfortunately, linker scripts are name based. This means that
   // expressions like *(.foo*) can refer to multiple input sections with
   // different flags. We cannot put them in different output sections or we
   // would produce wrong results for
   //
   // start = .; *(.foo.*) end = .; *(.bar)
   //
   // and a mapping of .foo1 and .bar1 to one section and .foo2 and .bar2 to
   // another. The problem is that there is no way to layout those output
   // sections such that the .foo sections are the only thing between the start
   // and end symbols.
   //
   // Given the above issues, we instead merge sections by name and error on
   // incompatible types and flags.
   TinyPtrVector<OutputSection *> &v = map[outsecName];
   for (OutputSection *sec : v) {
     if (sec->partition != isec->partition)
       continue;
 
     if (config->relocatable && (isec->flags & SHF_LINK_ORDER)) {
       // Merging two SHF_LINK_ORDER sections with different sh_link fields will
       // change their semantics, so we only merge them in -r links if they will
       // end up being linked to the same output section. The casts are fine
       // because everything in the map was created by the orphan placement code.
       auto *firstIsec = cast<InputSectionBase>(
           cast<InputSectionDescription>(sec->sectionCommands[0])
               ->sectionBases[0]);
       if (firstIsec->getLinkOrderDep()->getOutputSection() !=
           isec->getLinkOrderDep()->getOutputSection())
         continue;
     }
 
     sec->recordSection(isec);
     return nullptr;
   }
 
   OutputSection *sec = createSection(isec, outsecName);
   v.push_back(sec);
   return sec;
 }
 
 // Add sections that didn't match any sections command.
 void LinkerScript::addOrphanSections() {
   StringMap<TinyPtrVector<OutputSection *>> map;
   std::vector<OutputSection *> v;
 
   std::function<void(InputSectionBase *)> add;
   add = [&](InputSectionBase *s) {
     if (s->isLive() && !s->parent) {
       StringRef name = getOutputSectionName(s);
 
       if (config->orphanHandling == OrphanHandlingPolicy::Error)
         error(toString(s) + " is being placed in '" + name + "'");
       else if (config->orphanHandling == OrphanHandlingPolicy::Warn)
         warn(toString(s) + " is being placed in '" + name + "'");
 
       if (OutputSection *sec = findByName(sectionCommands, name)) {
         sec->recordSection(s);
       } else {
         if (OutputSection *os = addInputSec(map, s, name))
           v.push_back(os);
         assert(isa<MergeInputSection>(s) ||
                s->getOutputSection()->sectionIndex == UINT32_MAX);
       }
     }
 
     if (config->relocatable)
       for (InputSectionBase *depSec : s->dependentSections)
         if (depSec->flags & SHF_LINK_ORDER)
           add(depSec);
   };
 
   // For futher --emit-reloc handling code we need target output section
   // to be created before we create relocation output section, so we want
   // to create target sections first. We do not want priority handling
   // for synthetic sections because them are special.
   for (InputSectionBase *isec : inputSections) {
     // In -r links, SHF_LINK_ORDER sections are added while adding their parent
     // sections because we need to know the parent's output section before we
     // can select an output section for the SHF_LINK_ORDER section.
     if (config->relocatable && (isec->flags & SHF_LINK_ORDER))
       continue;
 
     if (auto *sec = dyn_cast<InputSection>(isec))
       if (InputSectionBase *rel = sec->getRelocatedSection())
         if (auto *relIS = dyn_cast_or_null<InputSectionBase>(rel->parent))
           add(relIS);
     add(isec);
   }
 
   // If no SECTIONS command was given, we should insert sections commands
   // before others, so that we can handle scripts which refers them,
   // for example: "foo = ABSOLUTE(ADDR(.text)));".
   // When SECTIONS command is present we just add all orphans to the end.
   if (hasSectionsCommand)
     sectionCommands.insert(sectionCommands.end(), v.begin(), v.end());
   else
     sectionCommands.insert(sectionCommands.begin(), v.begin(), v.end());
 }
 
 uint64_t LinkerScript::advance(uint64_t size, unsigned alignment) {
   bool isTbss =
       (ctx->outSec->flags & SHF_TLS) && ctx->outSec->type == SHT_NOBITS;
   uint64_t start = isTbss ? dot + ctx->threadBssOffset : dot;
   start = alignTo(start, alignment);
   uint64_t end = start + size;
 
   if (isTbss)
     ctx->threadBssOffset = end - dot;
   else
     dot = end;
   return end;
 }
 
 void LinkerScript::output(InputSection *s) {
   assert(ctx->outSec == s->getParent());
   uint64_t before = advance(0, 1);
   uint64_t pos = advance(s->getSize(), s->alignment);
   s->outSecOff = pos - s->getSize() - ctx->outSec->addr;
 
   // Update output section size after adding each section. This is so that
   // SIZEOF works correctly in the case below:
   // .foo { *(.aaa) a = SIZEOF(.foo); *(.bbb) }
   expandOutputSection(pos - before);
 }
 
 void LinkerScript::switchTo(OutputSection *sec) {
   ctx->outSec = sec;
 
   uint64_t before = advance(0, 1);
   ctx->outSec->addr = advance(0, ctx->outSec->alignment);
   expandMemoryRegions(ctx->outSec->addr - before);
 }
 
 // This function searches for a memory region to place the given output
 // section in. If found, a pointer to the appropriate memory region is
 // returned. Otherwise, a nullptr is returned.
 MemoryRegion *LinkerScript::findMemoryRegion(OutputSection *sec) {
   // If a memory region name was specified in the output section command,
   // then try to find that region first.
   if (!sec->memoryRegionName.empty()) {
     if (MemoryRegion *m = memoryRegions.lookup(sec->memoryRegionName))
       return m;
     error("memory region '" + sec->memoryRegionName + "' not declared");
     return nullptr;
   }
 
   // If at least one memory region is defined, all sections must
   // belong to some memory region. Otherwise, we don't need to do
   // anything for memory regions.
   if (memoryRegions.empty())
     return nullptr;
 
   // See if a region can be found by matching section flags.
   for (auto &pair : memoryRegions) {
     MemoryRegion *m = pair.second;
     if ((m->flags & sec->flags) && (m->negFlags & sec->flags) == 0)
       return m;
   }
 
   // Otherwise, no suitable region was found.
   if (sec->flags & SHF_ALLOC)
     error("no memory region specified for section '" + sec->name + "'");
   return nullptr;
 }
 
 static OutputSection *findFirstSection(PhdrEntry *load) {
   for (OutputSection *sec : outputSections)
     if (sec->ptLoad == load)
       return sec;
   return nullptr;
 }
 
 // This function assigns offsets to input sections and an output section
 // for a single sections command (e.g. ".text { *(.text); }").
 void LinkerScript::assignOffsets(OutputSection *sec) {
   if (!(sec->flags & SHF_ALLOC))
     dot = 0;
 
   ctx->memRegion = sec->memRegion;
   ctx->lmaRegion = sec->lmaRegion;
   if (ctx->memRegion)
     dot = ctx->memRegion->curPos;
 
   if ((sec->flags & SHF_ALLOC) && sec->addrExpr)
     setDot(sec->addrExpr, sec->location, false);
 
   // If the address of the section has been moved forward by an explicit
   // expression so that it now starts past the current curPos of the enclosing
   // region, we need to expand the current region to account for the space
   // between the previous section, if any, and the start of this section.
   if (ctx->memRegion && ctx->memRegion->curPos < dot)
     expandMemoryRegion(ctx->memRegion, dot - ctx->memRegion->curPos,
                        ctx->memRegion->name, sec->name);
 
   switchTo(sec);
 
   if (sec->lmaExpr)
     ctx->lmaOffset = sec->lmaExpr().getValue() - dot;
 
   if (MemoryRegion *mr = sec->lmaRegion)
     ctx->lmaOffset = mr->curPos - dot;
 
   // If neither AT nor AT> is specified for an allocatable section, the linker
   // will set the LMA such that the difference between VMA and LMA for the
   // section is the same as the preceding output section in the same region
   // https://sourceware.org/binutils/docs-2.20/ld/Output-Section-LMA.html
   // This, however, should only be done by the first "non-header" section
   // in the segment.
   if (PhdrEntry *l = ctx->outSec->ptLoad)
     if (sec == findFirstSection(l))
       l->lmaOffset = ctx->lmaOffset;
 
   // We can call this method multiple times during the creation of
   // thunks and want to start over calculation each time.
   sec->size = 0;
 
   // We visited SectionsCommands from processSectionCommands to
   // layout sections. Now, we visit SectionsCommands again to fix
   // section offsets.
   for (BaseCommand *base : sec->sectionCommands) {
     // This handles the assignments to symbol or to the dot.
     if (auto *cmd = dyn_cast<SymbolAssignment>(base)) {
       cmd->addr = dot;
       assignSymbol(cmd, true);
       cmd->size = dot - cmd->addr;
       continue;
     }
 
     // Handle BYTE(), SHORT(), LONG(), or QUAD().
     if (auto *cmd = dyn_cast<ByteCommand>(base)) {
       cmd->offset = dot - ctx->outSec->addr;
       dot += cmd->size;
       expandOutputSection(cmd->size);
       continue;
     }
 
     // Handle a single input section description command.
     // It calculates and assigns the offsets for each section and also
     // updates the output section size.
     for (InputSection *sec : cast<InputSectionDescription>(base)->sections)
       output(sec);
   }
 }
 
 static bool isDiscardable(OutputSection &sec) {
   if (sec.name == "/DISCARD/")
     return true;
 
   // We do not remove empty sections that are explicitly
   // assigned to any segment.
   if (!sec.phdrs.empty())
     return false;
 
   // We do not want to remove OutputSections with expressions that reference
   // symbols even if the OutputSection is empty. We want to ensure that the
   // expressions can be evaluated and report an error if they cannot.
   if (sec.expressionsUseSymbols)
     return false;
 
   // OutputSections may be referenced by name in ADDR and LOADADDR expressions,
   // as an empty Section can has a valid VMA and LMA we keep the OutputSection
   // to maintain the integrity of the other Expression.
   if (sec.usedInExpression)
     return false;
 
   for (BaseCommand *base : sec.sectionCommands) {
     if (auto cmd = dyn_cast<SymbolAssignment>(base))
       // Don't create empty output sections just for unreferenced PROVIDE
       // symbols.
       if (cmd->name != "." && !cmd->sym)
         continue;
 
     if (!isa<InputSectionDescription>(*base))
       return false;
   }
   return true;
 }
 
 void LinkerScript::adjustSectionsBeforeSorting() {
   // If the output section contains only symbol assignments, create a
   // corresponding output section. The issue is what to do with linker script
   // like ".foo : { symbol = 42; }". One option would be to convert it to
   // "symbol = 42;". That is, move the symbol out of the empty section
   // description. That seems to be what bfd does for this simple case. The
   // problem is that this is not completely general. bfd will give up and
   // create a dummy section too if there is a ". = . + 1" inside the section
   // for example.
   // Given that we want to create the section, we have to worry what impact
   // it will have on the link. For example, if we just create a section with
   // 0 for flags, it would change which PT_LOADs are created.
   // We could remember that particular section is dummy and ignore it in
   // other parts of the linker, but unfortunately there are quite a few places
   // that would need to change:
   //   * The program header creation.
   //   * The orphan section placement.
   //   * The address assignment.
   // The other option is to pick flags that minimize the impact the section
   // will have on the rest of the linker. That is why we copy the flags from
   // the previous sections. Only a few flags are needed to keep the impact low.
   uint64_t flags = SHF_ALLOC;
 
   for (BaseCommand *&cmd : sectionCommands) {
     auto *sec = dyn_cast<OutputSection>(cmd);
     if (!sec)
       continue;
 
     // Handle align (e.g. ".foo : ALIGN(16) { ... }").
     if (sec->alignExpr)
       sec->alignment =
           std::max<uint32_t>(sec->alignment, sec->alignExpr().getValue());
 
     // The input section might have been removed (if it was an empty synthetic
     // section), but we at least know the flags.
     if (sec->hasInputSections)
       flags = sec->flags;
 
     // We do not want to keep any special flags for output section
     // in case it is empty.
     bool isEmpty = getInputSections(sec).empty();
     if (isEmpty)
       sec->flags = flags & ((sec->nonAlloc ? 0 : (uint64_t)SHF_ALLOC) |
                             SHF_WRITE | SHF_EXECINSTR);
 
     if (isEmpty && isDiscardable(*sec)) {
       sec->markDead();
       cmd = nullptr;
     }
   }
 
   // It is common practice to use very generic linker scripts. So for any
   // given run some of the output sections in the script will be empty.
   // We could create corresponding empty output sections, but that would
   // clutter the output.
   // We instead remove trivially empty sections. The bfd linker seems even
   // more aggressive at removing them.
   llvm::erase_if(sectionCommands, [&](BaseCommand *base) { return !base; });
 }
 
 void LinkerScript::adjustSectionsAfterSorting() {
   // Try and find an appropriate memory region to assign offsets in.
   for (BaseCommand *base : sectionCommands) {
     if (auto *sec = dyn_cast<OutputSection>(base)) {
       if (!sec->lmaRegionName.empty()) {
         if (MemoryRegion *m = memoryRegions.lookup(sec->lmaRegionName))
           sec->lmaRegion = m;
         else
           error("memory region '" + sec->lmaRegionName + "' not declared");
       }
       sec->memRegion = findMemoryRegion(sec);
     }
   }
 
   // If output section command doesn't specify any segments,
   // and we haven't previously assigned any section to segment,
   // then we simply assign section to the very first load segment.
   // Below is an example of such linker script:
   // PHDRS { seg PT_LOAD; }
   // SECTIONS { .aaa : { *(.aaa) } }
   std::vector<StringRef> defPhdrs;
   auto firstPtLoad = llvm::find_if(phdrsCommands, [](const PhdrsCommand &cmd) {
     return cmd.type == PT_LOAD;
   });
   if (firstPtLoad != phdrsCommands.end())
     defPhdrs.push_back(firstPtLoad->name);
 
   // Walk the commands and propagate the program headers to commands that don't
   // explicitly specify them.
   for (BaseCommand *base : sectionCommands) {
     auto *sec = dyn_cast<OutputSection>(base);
     if (!sec)
       continue;
 
     if (sec->phdrs.empty()) {
       // To match the bfd linker script behaviour, only propagate program
       // headers to sections that are allocated.
       if (sec->flags & SHF_ALLOC)
         sec->phdrs = defPhdrs;
     } else {
       defPhdrs = sec->phdrs;
     }
   }
 }
 
 static uint64_t computeBase(uint64_t min, bool allocateHeaders) {
   // If there is no SECTIONS or if the linkerscript is explicit about program
   // headers, do our best to allocate them.
   if (!script->hasSectionsCommand || allocateHeaders)
     return 0;
   // Otherwise only allocate program headers if that would not add a page.
   return alignDown(min, config->maxPageSize);
 }
 
-// When the SECTIONS command is used, try to find an address for the file and
-// program headers output sections, which can be added to the first PT_LOAD
-// segment when program headers are created.
+// Try to find an address for the file and program headers output sections,
+// which were unconditionally added to the first PT_LOAD segment earlier.
 //
-// We check if the headers fit below the first allocated section. If there isn't
-// enough space for these sections, we'll remove them from the PT_LOAD segment,
-// and we'll also remove the PT_PHDR segment.
+// When using the default layout, we check if the headers fit below the first
+// allocated section. When using a linker script, we also check if the headers
+// are covered by the output section. This allows omitting the headers by not
+// leaving enough space for them in the linker script; this pattern is common
+// in embedded systems.
+//
+// If there isn't enough space for these sections, we'll remove them from the
+// PT_LOAD segment, and we'll also remove the PT_PHDR segment.
 void LinkerScript::allocateHeaders(std::vector<PhdrEntry *> &phdrs) {
   uint64_t min = std::numeric_limits<uint64_t>::max();
   for (OutputSection *sec : outputSections)
     if (sec->flags & SHF_ALLOC)
       min = std::min<uint64_t>(min, sec->addr);
 
   auto it = llvm::find_if(
       phdrs, [](const PhdrEntry *e) { return e->p_type == PT_LOAD; });
   if (it == phdrs.end())
     return;
   PhdrEntry *firstPTLoad = *it;
 
   bool hasExplicitHeaders =
       llvm::any_of(phdrsCommands, [](const PhdrsCommand &cmd) {
         return cmd.hasPhdrs || cmd.hasFilehdr;
       });
   bool paged = !config->omagic && !config->nmagic;
   uint64_t headerSize = getHeaderSize();
   if ((paged || hasExplicitHeaders) &&
       headerSize <= min - computeBase(min, hasExplicitHeaders)) {
     min = alignDown(min - headerSize, config->maxPageSize);
     Out::elfHeader->addr = min;
     Out::programHeaders->addr = min + Out::elfHeader->size;
     return;
   }
 
   // Error if we were explicitly asked to allocate headers.
   if (hasExplicitHeaders)
     error("could not allocate headers");
 
   Out::elfHeader->ptLoad = nullptr;
   Out::programHeaders->ptLoad = nullptr;
   firstPTLoad->firstSec = findFirstSection(firstPTLoad);
 
   llvm::erase_if(phdrs,
                  [](const PhdrEntry *e) { return e->p_type == PT_PHDR; });
 }
 
 LinkerScript::AddressState::AddressState() {
   for (auto &mri : script->memoryRegions) {
     MemoryRegion *mr = mri.second;
     mr->curPos = mr->origin;
   }
 }
 
+static uint64_t getInitialDot() {
+  // By default linker scripts use an initial value of 0 for '.',
+  // but prefer -image-base if set.
+  if (script->hasSectionsCommand)
+    return config->imageBase ? *config->imageBase : 0;
+
+  uint64_t startAddr = UINT64_MAX;
+  // The sections with -T<section> have been sorted in order of ascending
+  // address. We must lower startAddr if the lowest -T<section address> as
+  // calls to setDot() must be monotonically increasing.
+  for (auto &kv : config->sectionStartMap)
+    startAddr = std::min(startAddr, kv.second);
+  return std::min(startAddr, target->getImageBase() + elf::getHeaderSize());
+}
+
 // Here we assign addresses as instructed by linker script SECTIONS
 // sub-commands. Doing that allows us to use final VA values, so here
 // we also handle rest commands like symbol assignments and ASSERTs.
 // Returns a symbol that has changed its section or value, or nullptr if no
 // symbol has changed.
 const Defined *LinkerScript::assignAddresses() {
-  if (script->hasSectionsCommand) {
-    // With a linker script, assignment of addresses to headers is covered by
-    // allocateHeaders().
-    dot = config->imageBase.getValueOr(0);
-  } else {
-    // Assign addresses to headers right now.
-    dot = target->getImageBase();
-    Out::elfHeader->addr = dot;
-    Out::programHeaders->addr = dot + Out::elfHeader->size;
-    dot += getHeaderSize();
-  }
+  dot = getInitialDot();
 
   auto deleter = std::make_unique<AddressState>();
   ctx = deleter.get();
   errorOnMissingSection = true;
   switchTo(aether);
 
   SymbolAssignmentMap oldValues = getSymbolAssignmentValues(sectionCommands);
   for (BaseCommand *base : sectionCommands) {
     if (auto *cmd = dyn_cast<SymbolAssignment>(base)) {
       cmd->addr = dot;
       assignSymbol(cmd, false);
       cmd->size = dot - cmd->addr;
       continue;
     }
     assignOffsets(cast<OutputSection>(base));
   }
 
   ctx = nullptr;
   return getChangedSymbolAssignment(oldValues);
 }
 
 // Creates program headers as instructed by PHDRS linker script command.
 std::vector<PhdrEntry *> LinkerScript::createPhdrs() {
   std::vector<PhdrEntry *> ret;
 
   // Process PHDRS and FILEHDR keywords because they are not
   // real output sections and cannot be added in the following loop.
   for (const PhdrsCommand &cmd : phdrsCommands) {
     PhdrEntry *phdr = make<PhdrEntry>(cmd.type, cmd.flags ? *cmd.flags : PF_R);
 
     if (cmd.hasFilehdr)
       phdr->add(Out::elfHeader);
     if (cmd.hasPhdrs)
       phdr->add(Out::programHeaders);
 
     if (cmd.lmaExpr) {
       phdr->p_paddr = cmd.lmaExpr().getValue();
       phdr->hasLMA = true;
     }
     ret.push_back(phdr);
   }
 
   // Add output sections to program headers.
   for (OutputSection *sec : outputSections) {
     // Assign headers specified by linker script
     for (size_t id : getPhdrIndices(sec)) {
       ret[id]->add(sec);
       if (!phdrsCommands[id].flags.hasValue())
         ret[id]->p_flags |= sec->getPhdrFlags();
     }
   }
   return ret;
 }
 
 // Returns true if we should emit an .interp section.
 //
 // We usually do. But if PHDRS commands are given, and
 // no PT_INTERP is there, there's no place to emit an
 // .interp, so we don't do that in that case.
 bool LinkerScript::needsInterpSection() {
   if (phdrsCommands.empty())
     return true;
   for (PhdrsCommand &cmd : phdrsCommands)
     if (cmd.type == PT_INTERP)
       return true;
   return false;
 }
 
 ExprValue LinkerScript::getSymbolValue(StringRef name, const Twine &loc) {
   if (name == ".") {
     if (ctx)
       return {ctx->outSec, false, dot - ctx->outSec->addr, loc};
     error(loc + ": unable to get location counter value");
     return 0;
   }
 
   if (Symbol *sym = symtab->find(name)) {
     if (auto *ds = dyn_cast<Defined>(sym))
       return {ds->section, false, ds->value, loc};
     if (isa<SharedSymbol>(sym))
       if (!errorOnMissingSection)
         return {nullptr, false, 0, loc};
   }
 
   error(loc + ": symbol not found: " + name);
   return 0;
 }
 
 // Returns the index of the segment named Name.
 static Optional<size_t> getPhdrIndex(ArrayRef<PhdrsCommand> vec,
                                      StringRef name) {
   for (size_t i = 0; i < vec.size(); ++i)
     if (vec[i].name == name)
       return i;
   return None;
 }
 
 // Returns indices of ELF headers containing specific section. Each index is a
 // zero based number of ELF header listed within PHDRS {} script block.
 std::vector<size_t> LinkerScript::getPhdrIndices(OutputSection *cmd) {
   std::vector<size_t> ret;
 
   for (StringRef s : cmd->phdrs) {
     if (Optional<size_t> idx = getPhdrIndex(phdrsCommands, s))
       ret.push_back(*idx);
     else if (s != "NONE")
       error(cmd->location + ": section header '" + s +
             "' is not listed in PHDRS");
   }
   return ret;
 }
 
 } // namespace elf
 } // namespace lld
Index: projects/clang1000-import/contrib/llvm-project/lld/ELF/Writer.cpp
===================================================================
--- projects/clang1000-import/contrib/llvm-project/lld/ELF/Writer.cpp	(revision 357258)
+++ projects/clang1000-import/contrib/llvm-project/lld/ELF/Writer.cpp	(revision 357259)
@@ -1,2730 +1,2729 @@
 //===- Writer.cpp ---------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "Writer.h"
 #include "AArch64ErrataFix.h"
 #include "ARMErrataFix.h"
 #include "CallGraphSort.h"
 #include "Config.h"
 #include "LinkerScript.h"
 #include "MapFile.h"
 #include "OutputSections.h"
 #include "Relocations.h"
 #include "SymbolTable.h"
 #include "Symbols.h"
 #include "SyntheticSections.h"
 #include "Target.h"
 #include "lld/Common/Filesystem.h"
 #include "lld/Common/Memory.h"
 #include "lld/Common/Strings.h"
 #include "lld/Common/Threads.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/RandomNumberGenerator.h"
 #include "llvm/Support/SHA1.h"
 #include "llvm/Support/xxhash.h"
 #include <climits>
 
 using namespace llvm;
 using namespace llvm::ELF;
 using namespace llvm::object;
 using namespace llvm::support;
 using namespace llvm::support::endian;
 
 namespace lld {
 namespace elf {
 namespace {
 // The writer writes a SymbolTable result to a file.
 template <class ELFT> class Writer {
 public:
   Writer() : buffer(errorHandler().outputBuffer) {}
   using Elf_Shdr = typename ELFT::Shdr;
   using Elf_Ehdr = typename ELFT::Ehdr;
   using Elf_Phdr = typename ELFT::Phdr;
 
   void run();
 
 private:
   void copyLocalSymbols();
   void addSectionSymbols();
   void forEachRelSec(llvm::function_ref<void(InputSectionBase &)> fn);
   void sortSections();
   void resolveShfLinkOrder();
   void finalizeAddressDependentContent();
   void sortInputSections();
   void finalizeSections();
   void checkExecuteOnly();
   void setReservedSymbolSections();
 
   std::vector<PhdrEntry *> createPhdrs(Partition &part);
   void addPhdrForSection(Partition &part, unsigned shType, unsigned pType,
                          unsigned pFlags);
   void assignFileOffsets();
   void assignFileOffsetsBinary();
   void setPhdrs(Partition &part);
   void checkSections();
   void fixSectionAlignments();
   void openFile();
   void writeTrapInstr();
   void writeHeader();
   void writeSections();
   void writeSectionsBinary();
   void writeBuildId();
 
   std::unique_ptr<FileOutputBuffer> &buffer;
 
   void addRelIpltSymbols();
   void addStartEndSymbols();
   void addStartStopSymbols(OutputSection *sec);
 
   uint64_t fileSize;
   uint64_t sectionHeaderOff;
 };
 } // anonymous namespace
 
 static bool isSectionPrefix(StringRef prefix, StringRef name) {
   return name.startswith(prefix) || name == prefix.drop_back();
 }
 
 StringRef getOutputSectionName(const InputSectionBase *s) {
   if (config->relocatable)
     return s->name;
 
   // This is for --emit-relocs. If .text.foo is emitted as .text.bar, we want
   // to emit .rela.text.foo as .rela.text.bar for consistency (this is not
   // technically required, but not doing it is odd). This code guarantees that.
   if (auto *isec = dyn_cast<InputSection>(s)) {
     if (InputSectionBase *rel = isec->getRelocatedSection()) {
       OutputSection *out = rel->getOutputSection();
       if (s->type == SHT_RELA)
         return saver.save(".rela" + out->name);
       return saver.save(".rel" + out->name);
     }
   }
 
   // This check is for -z keep-text-section-prefix.  This option separates text
   // sections with prefix ".text.hot", ".text.unlikely", ".text.startup" or
   // ".text.exit".
   // When enabled, this allows identifying the hot code region (.text.hot) in
   // the final binary which can be selectively mapped to huge pages or mlocked,
   // for instance.
   if (config->zKeepTextSectionPrefix)
     for (StringRef v :
          {".text.hot.", ".text.unlikely.", ".text.startup.", ".text.exit."})
       if (isSectionPrefix(v, s->name))
         return v.drop_back();
 
   for (StringRef v :
        {".text.", ".rodata.", ".data.rel.ro.", ".data.", ".bss.rel.ro.",
         ".bss.", ".init_array.", ".fini_array.", ".ctors.", ".dtors.", ".tbss.",
         ".gcc_except_table.", ".tdata.", ".ARM.exidx.", ".ARM.extab."})
     if (isSectionPrefix(v, s->name))
       return v.drop_back();
 
   // CommonSection is identified as "COMMON" in linker scripts.
   // By default, it should go to .bss section.
   if (s->name == "COMMON")
     return ".bss";
 
   return s->name;
 }
 
 static bool needsInterpSection() {
   return !config->relocatable && !config->shared &&
          !config->dynamicLinker.empty() && script->needsInterpSection();
 }
 
 template <class ELFT> void writeResult() { Writer<ELFT>().run(); }
 
 static void removeEmptyPTLoad(std::vector<PhdrEntry *> &phdrs) {
   llvm::erase_if(phdrs, [&](const PhdrEntry *p) {
     if (p->p_type != PT_LOAD)
       return false;
     if (!p->firstSec)
       return true;
     uint64_t size = p->lastSec->addr + p->lastSec->size - p->firstSec->addr;
     return size == 0;
   });
 }
 
 void copySectionsIntoPartitions() {
   std::vector<InputSectionBase *> newSections;
   for (unsigned part = 2; part != partitions.size() + 1; ++part) {
     for (InputSectionBase *s : inputSections) {
       if (!(s->flags & SHF_ALLOC) || !s->isLive())
         continue;
       InputSectionBase *copy;
       if (s->type == SHT_NOTE)
         copy = make<InputSection>(cast<InputSection>(*s));
       else if (auto *es = dyn_cast<EhInputSection>(s))
         copy = make<EhInputSection>(*es);
       else
         continue;
       copy->partition = part;
       newSections.push_back(copy);
     }
   }
 
   inputSections.insert(inputSections.end(), newSections.begin(),
                        newSections.end());
 }
 
 void combineEhSections() {
   for (InputSectionBase *&s : inputSections) {
     // Ignore dead sections and the partition end marker (.part.end),
     // whose partition number is out of bounds.
     if (!s->isLive() || s->partition == 255)
       continue;
 
     Partition &part = s->getPartition();
     if (auto *es = dyn_cast<EhInputSection>(s)) {
       part.ehFrame->addSection(es);
       s = nullptr;
     } else if (s->kind() == SectionBase::Regular && part.armExidx &&
                part.armExidx->addSection(cast<InputSection>(s))) {
       s = nullptr;
     }
   }
 
   std::vector<InputSectionBase *> &v = inputSections;
   v.erase(std::remove(v.begin(), v.end(), nullptr), v.end());
 }
 
 static Defined *addOptionalRegular(StringRef name, SectionBase *sec,
                                    uint64_t val, uint8_t stOther = STV_HIDDEN,
                                    uint8_t binding = STB_GLOBAL) {
   Symbol *s = symtab->find(name);
   if (!s || s->isDefined())
     return nullptr;
 
   s->resolve(Defined{/*file=*/nullptr, name, binding, stOther, STT_NOTYPE, val,
                      /*size=*/0, sec});
   return cast<Defined>(s);
 }
 
 static Defined *addAbsolute(StringRef name) {
   Symbol *sym = symtab->addSymbol(Defined{nullptr, name, STB_GLOBAL, STV_HIDDEN,
                                           STT_NOTYPE, 0, 0, nullptr});
   return cast<Defined>(sym);
 }
 
 // The linker is expected to define some symbols depending on
 // the linking result. This function defines such symbols.
 void addReservedSymbols() {
   if (config->emachine == EM_MIPS) {
     // Define _gp for MIPS. st_value of _gp symbol will be updated by Writer
     // so that it points to an absolute address which by default is relative
     // to GOT. Default offset is 0x7ff0.
     // See "Global Data Symbols" in Chapter 6 in the following document:
     // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
     ElfSym::mipsGp = addAbsolute("_gp");
 
     // On MIPS O32 ABI, _gp_disp is a magic symbol designates offset between
     // start of function and 'gp' pointer into GOT.
     if (symtab->find("_gp_disp"))
       ElfSym::mipsGpDisp = addAbsolute("_gp_disp");
 
     // The __gnu_local_gp is a magic symbol equal to the current value of 'gp'
     // pointer. This symbol is used in the code generated by .cpload pseudo-op
     // in case of using -mno-shared option.
     // https://sourceware.org/ml/binutils/2004-12/msg00094.html
     if (symtab->find("__gnu_local_gp"))
       ElfSym::mipsLocalGp = addAbsolute("__gnu_local_gp");
   } else if (config->emachine == EM_PPC) {
     // glibc *crt1.o has a undefined reference to _SDA_BASE_. Since we don't
     // support Small Data Area, define it arbitrarily as 0.
     addOptionalRegular("_SDA_BASE_", nullptr, 0, STV_HIDDEN);
   }
 
   // The Power Architecture 64-bit v2 ABI defines a TableOfContents (TOC) which
   // combines the typical ELF GOT with the small data sections. It commonly
   // includes .got .toc .sdata .sbss. The .TOC. symbol replaces both
   // _GLOBAL_OFFSET_TABLE_ and _SDA_BASE_ from the 32-bit ABI. It is used to
   // represent the TOC base which is offset by 0x8000 bytes from the start of
   // the .got section.
   // We do not allow _GLOBAL_OFFSET_TABLE_ to be defined by input objects as the
   // correctness of some relocations depends on its value.
   StringRef gotSymName =
       (config->emachine == EM_PPC64) ? ".TOC." : "_GLOBAL_OFFSET_TABLE_";
 
   if (Symbol *s = symtab->find(gotSymName)) {
     if (s->isDefined()) {
       error(toString(s->file) + " cannot redefine linker defined symbol '" +
             gotSymName + "'");
       return;
     }
 
     uint64_t gotOff = 0;
     if (config->emachine == EM_PPC64)
       gotOff = 0x8000;
 
     s->resolve(Defined{/*file=*/nullptr, gotSymName, STB_GLOBAL, STV_HIDDEN,
                        STT_NOTYPE, gotOff, /*size=*/0, Out::elfHeader});
     ElfSym::globalOffsetTable = cast<Defined>(s);
   }
 
   // __ehdr_start is the location of ELF file headers. Note that we define
   // this symbol unconditionally even when using a linker script, which
   // differs from the behavior implemented by GNU linker which only define
   // this symbol if ELF headers are in the memory mapped segment.
   addOptionalRegular("__ehdr_start", Out::elfHeader, 0, STV_HIDDEN);
 
   // __executable_start is not documented, but the expectation of at
   // least the Android libc is that it points to the ELF header.
   addOptionalRegular("__executable_start", Out::elfHeader, 0, STV_HIDDEN);
 
   // __dso_handle symbol is passed to cxa_finalize as a marker to identify
   // each DSO. The address of the symbol doesn't matter as long as they are
   // different in different DSOs, so we chose the start address of the DSO.
   addOptionalRegular("__dso_handle", Out::elfHeader, 0, STV_HIDDEN);
 
   // If linker script do layout we do not need to create any standard symbols.
   if (script->hasSectionsCommand)
     return;
 
   auto add = [](StringRef s, int64_t pos) {
     return addOptionalRegular(s, Out::elfHeader, pos, STV_DEFAULT);
   };
 
   ElfSym::bss = add("__bss_start", 0);
   ElfSym::end1 = add("end", -1);
   ElfSym::end2 = add("_end", -1);
   ElfSym::etext1 = add("etext", -1);
   ElfSym::etext2 = add("_etext", -1);
   ElfSym::edata1 = add("edata", -1);
   ElfSym::edata2 = add("_edata", -1);
 }
 
 static OutputSection *findSection(StringRef name, unsigned partition = 1) {
   for (BaseCommand *base : script->sectionCommands)
     if (auto *sec = dyn_cast<OutputSection>(base))
       if (sec->name == name && sec->partition == partition)
         return sec;
   return nullptr;
 }
 
 template <class ELFT> void createSyntheticSections() {
   // Initialize all pointers with NULL. This is needed because
   // you can call lld::elf::main more than once as a library.
   memset(&Out::first, 0, sizeof(Out));
 
   // Add the .interp section first because it is not a SyntheticSection.
   // The removeUnusedSyntheticSections() function relies on the
   // SyntheticSections coming last.
   if (needsInterpSection()) {
     for (size_t i = 1; i <= partitions.size(); ++i) {
       InputSection *sec = createInterpSection();
       sec->partition = i;
       inputSections.push_back(sec);
     }
   }
 
   auto add = [](SyntheticSection *sec) { inputSections.push_back(sec); };
 
   in.shStrTab = make<StringTableSection>(".shstrtab", false);
 
   Out::programHeaders = make<OutputSection>("", 0, SHF_ALLOC);
   Out::programHeaders->alignment = config->wordsize;
 
   if (config->strip != StripPolicy::All) {
     in.strTab = make<StringTableSection>(".strtab", false);
     in.symTab = make<SymbolTableSection<ELFT>>(*in.strTab);
     in.symTabShndx = make<SymtabShndxSection>();
   }
 
   in.bss = make<BssSection>(".bss", 0, 1);
   add(in.bss);
 
   // If there is a SECTIONS command and a .data.rel.ro section name use name
   // .data.rel.ro.bss so that we match in the .data.rel.ro output section.
   // This makes sure our relro is contiguous.
   bool hasDataRelRo =
       script->hasSectionsCommand && findSection(".data.rel.ro", 0);
   in.bssRelRo =
       make<BssSection>(hasDataRelRo ? ".data.rel.ro.bss" : ".bss.rel.ro", 0, 1);
   add(in.bssRelRo);
 
   // Add MIPS-specific sections.
   if (config->emachine == EM_MIPS) {
     if (!config->shared && config->hasDynSymTab) {
       in.mipsRldMap = make<MipsRldMapSection>();
       add(in.mipsRldMap);
     }
     if (auto *sec = MipsAbiFlagsSection<ELFT>::create())
       add(sec);
     if (auto *sec = MipsOptionsSection<ELFT>::create())
       add(sec);
     if (auto *sec = MipsReginfoSection<ELFT>::create())
       add(sec);
   }
 
   StringRef relaDynName = config->isRela ? ".rela.dyn" : ".rel.dyn";
 
   for (Partition &part : partitions) {
     auto add = [&](SyntheticSection *sec) {
       sec->partition = part.getNumber();
       inputSections.push_back(sec);
     };
 
     if (!part.name.empty()) {
       part.elfHeader = make<PartitionElfHeaderSection<ELFT>>();
       part.elfHeader->name = part.name;
       add(part.elfHeader);
 
       part.programHeaders = make<PartitionProgramHeadersSection<ELFT>>();
       add(part.programHeaders);
     }
 
     if (config->buildId != BuildIdKind::None) {
       part.buildId = make<BuildIdSection>();
       add(part.buildId);
     }
 
     part.dynStrTab = make<StringTableSection>(".dynstr", true);
     part.dynSymTab = make<SymbolTableSection<ELFT>>(*part.dynStrTab);
     part.dynamic = make<DynamicSection<ELFT>>();
     if (config->androidPackDynRelocs)
       part.relaDyn = make<AndroidPackedRelocationSection<ELFT>>(relaDynName);
     else
       part.relaDyn =
           make<RelocationSection<ELFT>>(relaDynName, config->zCombreloc);
 
     if (config->hasDynSymTab) {
       part.dynSymTab = make<SymbolTableSection<ELFT>>(*part.dynStrTab);
       add(part.dynSymTab);
 
       part.verSym = make<VersionTableSection>();
       add(part.verSym);
 
       if (!namedVersionDefs().empty()) {
         part.verDef = make<VersionDefinitionSection>();
         add(part.verDef);
       }
 
       part.verNeed = make<VersionNeedSection<ELFT>>();
       add(part.verNeed);
 
       if (config->gnuHash) {
         part.gnuHashTab = make<GnuHashTableSection>();
         add(part.gnuHashTab);
       }
 
       if (config->sysvHash) {
         part.hashTab = make<HashTableSection>();
         add(part.hashTab);
       }
 
       add(part.dynamic);
       add(part.dynStrTab);
       add(part.relaDyn);
     }
 
     if (config->relrPackDynRelocs) {
       part.relrDyn = make<RelrSection<ELFT>>();
       add(part.relrDyn);
     }
 
     if (!config->relocatable) {
       if (config->ehFrameHdr) {
         part.ehFrameHdr = make<EhFrameHeader>();
         add(part.ehFrameHdr);
       }
       part.ehFrame = make<EhFrameSection>();
       add(part.ehFrame);
     }
 
     if (config->emachine == EM_ARM && !config->relocatable) {
       // The ARMExidxsyntheticsection replaces all the individual .ARM.exidx
       // InputSections.
       part.armExidx = make<ARMExidxSyntheticSection>();
       add(part.armExidx);
     }
   }
 
   if (partitions.size() != 1) {
     // Create the partition end marker. This needs to be in partition number 255
     // so that it is sorted after all other partitions. It also has other
     // special handling (see createPhdrs() and combineEhSections()).
     in.partEnd = make<BssSection>(".part.end", config->maxPageSize, 1);
     in.partEnd->partition = 255;
     add(in.partEnd);
 
     in.partIndex = make<PartitionIndexSection>();
     addOptionalRegular("__part_index_begin", in.partIndex, 0);
     addOptionalRegular("__part_index_end", in.partIndex,
                        in.partIndex->getSize());
     add(in.partIndex);
   }
 
   // Add .got. MIPS' .got is so different from the other archs,
   // it has its own class.
   if (config->emachine == EM_MIPS) {
     in.mipsGot = make<MipsGotSection>();
     add(in.mipsGot);
   } else {
     in.got = make<GotSection>();
     add(in.got);
   }
 
   if (config->emachine == EM_PPC) {
     in.ppc32Got2 = make<PPC32Got2Section>();
     add(in.ppc32Got2);
   }
 
   if (config->emachine == EM_PPC64) {
     in.ppc64LongBranchTarget = make<PPC64LongBranchTargetSection>();
     add(in.ppc64LongBranchTarget);
   }
 
   in.gotPlt = make<GotPltSection>();
   add(in.gotPlt);
   in.igotPlt = make<IgotPltSection>();
   add(in.igotPlt);
 
   // _GLOBAL_OFFSET_TABLE_ is defined relative to either .got.plt or .got. Treat
   // it as a relocation and ensure the referenced section is created.
   if (ElfSym::globalOffsetTable && config->emachine != EM_MIPS) {
     if (target->gotBaseSymInGotPlt)
       in.gotPlt->hasGotPltOffRel = true;
     else
       in.got->hasGotOffRel = true;
   }
 
   if (config->gdbIndex)
     add(GdbIndexSection::create<ELFT>());
 
   // We always need to add rel[a].plt to output if it has entries.
   // Even for static linking it can contain R_[*]_IRELATIVE relocations.
   in.relaPlt = make<RelocationSection<ELFT>>(
       config->isRela ? ".rela.plt" : ".rel.plt", /*sort=*/false);
   add(in.relaPlt);
 
   // The relaIplt immediately follows .rel[a].dyn to ensure that the IRelative
   // relocations are processed last by the dynamic loader. We cannot place the
   // iplt section in .rel.dyn when Android relocation packing is enabled because
   // that would cause a section type mismatch. However, because the Android
   // dynamic loader reads .rel.plt after .rel.dyn, we can get the desired
   // behaviour by placing the iplt section in .rel.plt.
   in.relaIplt = make<RelocationSection<ELFT>>(
       config->androidPackDynRelocs ? in.relaPlt->name : relaDynName,
       /*sort=*/false);
   add(in.relaIplt);
 
   if ((config->emachine == EM_386 || config->emachine == EM_X86_64) &&
       (config->andFeatures & GNU_PROPERTY_X86_FEATURE_1_IBT)) {
     in.ibtPlt = make<IBTPltSection>();
     add(in.ibtPlt);
   }
 
   in.plt = make<PltSection>();
   add(in.plt);
   in.iplt = make<IpltSection>();
   add(in.iplt);
 
   if (config->andFeatures)
     add(make<GnuPropertySection>());
 
   // .note.GNU-stack is always added when we are creating a re-linkable
   // object file. Other linkers are using the presence of this marker
   // section to control the executable-ness of the stack area, but that
   // is irrelevant these days. Stack area should always be non-executable
   // by default. So we emit this section unconditionally.
   if (config->relocatable)
     add(make<GnuStackSection>());
 
   if (in.symTab)
     add(in.symTab);
   if (in.symTabShndx)
     add(in.symTabShndx);
   add(in.shStrTab);
   if (in.strTab)
     add(in.strTab);
 }
 
 // The main function of the writer.
 template <class ELFT> void Writer<ELFT>::run() {
   if (config->discard != DiscardPolicy::All)
     copyLocalSymbols();
 
   if (config->copyRelocs)
     addSectionSymbols();
 
   // Now that we have a complete set of output sections. This function
   // completes section contents. For example, we need to add strings
   // to the string table, and add entries to .got and .plt.
   // finalizeSections does that.
   finalizeSections();
   checkExecuteOnly();
   if (errorCount())
     return;
 
   // If -compressed-debug-sections is specified, we need to compress
   // .debug_* sections. Do it right now because it changes the size of
   // output sections.
   for (OutputSection *sec : outputSections)
     sec->maybeCompress<ELFT>();
 
-  if (script->hasSectionsCommand)
-    script->allocateHeaders(mainPart->phdrs);
+  script->allocateHeaders(mainPart->phdrs);
 
   // Remove empty PT_LOAD to avoid causing the dynamic linker to try to mmap a
   // 0 sized region. This has to be done late since only after assignAddresses
   // we know the size of the sections.
   for (Partition &part : partitions)
     removeEmptyPTLoad(part.phdrs);
 
   if (!config->oFormatBinary)
     assignFileOffsets();
   else
     assignFileOffsetsBinary();
 
   for (Partition &part : partitions)
     setPhdrs(part);
 
   if (config->relocatable)
     for (OutputSection *sec : outputSections)
       sec->addr = 0;
 
   if (config->checkSections)
     checkSections();
 
   // It does not make sense try to open the file if we have error already.
   if (errorCount())
     return;
   // Write the result down to a file.
   openFile();
   if (errorCount())
     return;
 
   if (!config->oFormatBinary) {
     if (config->zSeparate != SeparateSegmentKind::None)
       writeTrapInstr();
     writeHeader();
     writeSections();
   } else {
     writeSectionsBinary();
   }
 
   // Backfill .note.gnu.build-id section content. This is done at last
   // because the content is usually a hash value of the entire output file.
   writeBuildId();
   if (errorCount())
     return;
 
   // Handle -Map and -cref options.
   writeMapFile();
   writeCrossReferenceTable();
   if (errorCount())
     return;
 
   if (auto e = buffer->commit())
     error("failed to write to the output file: " + toString(std::move(e)));
 }
 
 static bool shouldKeepInSymtab(const Defined &sym) {
   if (sym.isSection())
     return false;
 
   if (config->discard == DiscardPolicy::None)
     return true;
 
   // If -emit-reloc is given, all symbols including local ones need to be
   // copied because they may be referenced by relocations.
   if (config->emitRelocs)
     return true;
 
   // In ELF assembly .L symbols are normally discarded by the assembler.
   // If the assembler fails to do so, the linker discards them if
   // * --discard-locals is used.
   // * The symbol is in a SHF_MERGE section, which is normally the reason for
   //   the assembler keeping the .L symbol.
   StringRef name = sym.getName();
   bool isLocal = name.startswith(".L") || name.empty();
   if (!isLocal)
     return true;
 
   if (config->discard == DiscardPolicy::Locals)
     return false;
 
   SectionBase *sec = sym.section;
   return !sec || !(sec->flags & SHF_MERGE);
 }
 
 static bool includeInSymtab(const Symbol &b) {
   if (!b.isLocal() && !b.isUsedInRegularObj)
     return false;
 
   if (auto *d = dyn_cast<Defined>(&b)) {
     // Always include absolute symbols.
     SectionBase *sec = d->section;
     if (!sec)
       return true;
     sec = sec->repl;
 
     // Exclude symbols pointing to garbage-collected sections.
     if (isa<InputSectionBase>(sec) && !sec->isLive())
       return false;
 
     if (auto *s = dyn_cast<MergeInputSection>(sec))
       if (!s->getSectionPiece(d->value)->live)
         return false;
     return true;
   }
   return b.used;
 }
 
 // Local symbols are not in the linker's symbol table. This function scans
 // each object file's symbol table to copy local symbols to the output.
 template <class ELFT> void Writer<ELFT>::copyLocalSymbols() {
   if (!in.symTab)
     return;
   for (InputFile *file : objectFiles) {
     ObjFile<ELFT> *f = cast<ObjFile<ELFT>>(file);
     for (Symbol *b : f->getLocalSymbols()) {
       if (!b->isLocal())
         fatal(toString(f) +
               ": broken object: getLocalSymbols returns a non-local symbol");
       auto *dr = dyn_cast<Defined>(b);
 
       // No reason to keep local undefined symbol in symtab.
       if (!dr)
         continue;
       if (!includeInSymtab(*b))
         continue;
       if (!shouldKeepInSymtab(*dr))
         continue;
       in.symTab->addSymbol(b);
     }
   }
 }
 
 // Create a section symbol for each output section so that we can represent
 // relocations that point to the section. If we know that no relocation is
 // referring to a section (that happens if the section is a synthetic one), we
 // don't create a section symbol for that section.
 template <class ELFT> void Writer<ELFT>::addSectionSymbols() {
   for (BaseCommand *base : script->sectionCommands) {
     auto *sec = dyn_cast<OutputSection>(base);
     if (!sec)
       continue;
     auto i = llvm::find_if(sec->sectionCommands, [](BaseCommand *base) {
       if (auto *isd = dyn_cast<InputSectionDescription>(base))
         return !isd->sections.empty();
       return false;
     });
     if (i == sec->sectionCommands.end())
       continue;
     InputSectionBase *isec = cast<InputSectionDescription>(*i)->sections[0];
 
     // Relocations are not using REL[A] section symbols.
     if (isec->type == SHT_REL || isec->type == SHT_RELA)
       continue;
 
     // Unlike other synthetic sections, mergeable output sections contain data
     // copied from input sections, and there may be a relocation pointing to its
     // contents if -r or -emit-reloc are given.
     if (isa<SyntheticSection>(isec) && !(isec->flags & SHF_MERGE))
       continue;
 
     auto *sym =
         make<Defined>(isec->file, "", STB_LOCAL, /*stOther=*/0, STT_SECTION,
                       /*value=*/0, /*size=*/0, isec);
     in.symTab->addSymbol(sym);
   }
 }
 
 // Today's loaders have a feature to make segments read-only after
 // processing dynamic relocations to enhance security. PT_GNU_RELRO
 // is defined for that.
 //
 // This function returns true if a section needs to be put into a
 // PT_GNU_RELRO segment.
 static bool isRelroSection(const OutputSection *sec) {
   if (!config->zRelro)
     return false;
 
   uint64_t flags = sec->flags;
 
   // Non-allocatable or non-writable sections don't need RELRO because
   // they are not writable or not even mapped to memory in the first place.
   // RELRO is for sections that are essentially read-only but need to
   // be writable only at process startup to allow dynamic linker to
   // apply relocations.
   if (!(flags & SHF_ALLOC) || !(flags & SHF_WRITE))
     return false;
 
   // Once initialized, TLS data segments are used as data templates
   // for a thread-local storage. For each new thread, runtime
   // allocates memory for a TLS and copy templates there. No thread
   // are supposed to use templates directly. Thus, it can be in RELRO.
   if (flags & SHF_TLS)
     return true;
 
   // .init_array, .preinit_array and .fini_array contain pointers to
   // functions that are executed on process startup or exit. These
   // pointers are set by the static linker, and they are not expected
   // to change at runtime. But if you are an attacker, you could do
   // interesting things by manipulating pointers in .fini_array, for
   // example. So they are put into RELRO.
   uint32_t type = sec->type;
   if (type == SHT_INIT_ARRAY || type == SHT_FINI_ARRAY ||
       type == SHT_PREINIT_ARRAY)
     return true;
 
   // .got contains pointers to external symbols. They are resolved by
   // the dynamic linker when a module is loaded into memory, and after
   // that they are not expected to change. So, it can be in RELRO.
   if (in.got && sec == in.got->getParent())
     return true;
 
   // .toc is a GOT-ish section for PowerPC64. Their contents are accessed
   // through r2 register, which is reserved for that purpose. Since r2 is used
   // for accessing .got as well, .got and .toc need to be close enough in the
   // virtual address space. Usually, .toc comes just after .got. Since we place
   // .got into RELRO, .toc needs to be placed into RELRO too.
   if (sec->name.equals(".toc"))
     return true;
 
   // .got.plt contains pointers to external function symbols. They are
   // by default resolved lazily, so we usually cannot put it into RELRO.
   // However, if "-z now" is given, the lazy symbol resolution is
   // disabled, which enables us to put it into RELRO.
   if (sec == in.gotPlt->getParent())
     return config->zNow;
 
   // .dynamic section contains data for the dynamic linker, and
   // there's no need to write to it at runtime, so it's better to put
   // it into RELRO.
   if (sec->name == ".dynamic")
     return true;
 
   // Sections with some special names are put into RELRO. This is a
   // bit unfortunate because section names shouldn't be significant in
   // ELF in spirit. But in reality many linker features depend on
   // magic section names.
   StringRef s = sec->name;
   return s == ".data.rel.ro" || s == ".bss.rel.ro" || s == ".ctors" ||
          s == ".dtors" || s == ".jcr" || s == ".eh_frame" ||
          s == ".openbsd.randomdata";
 }
 
 // We compute a rank for each section. The rank indicates where the
 // section should be placed in the file.  Instead of using simple
 // numbers (0,1,2...), we use a series of flags. One for each decision
 // point when placing the section.
 // Using flags has two key properties:
 // * It is easy to check if a give branch was taken.
 // * It is easy two see how similar two ranks are (see getRankProximity).
 enum RankFlags {
   RF_NOT_ADDR_SET = 1 << 27,
   RF_NOT_ALLOC = 1 << 26,
   RF_PARTITION = 1 << 18, // Partition number (8 bits)
   RF_NOT_PART_EHDR = 1 << 17,
   RF_NOT_PART_PHDR = 1 << 16,
   RF_NOT_INTERP = 1 << 15,
   RF_NOT_NOTE = 1 << 14,
   RF_WRITE = 1 << 13,
   RF_EXEC_WRITE = 1 << 12,
   RF_EXEC = 1 << 11,
   RF_RODATA = 1 << 10,
   RF_NOT_RELRO = 1 << 9,
   RF_NOT_TLS = 1 << 8,
   RF_BSS = 1 << 7,
   RF_PPC_NOT_TOCBSS = 1 << 6,
   RF_PPC_TOCL = 1 << 5,
   RF_PPC_TOC = 1 << 4,
   RF_PPC_GOT = 1 << 3,
   RF_PPC_BRANCH_LT = 1 << 2,
   RF_MIPS_GPREL = 1 << 1,
   RF_MIPS_NOT_GOT = 1 << 0
 };
 
 static unsigned getSectionRank(const OutputSection *sec) {
   unsigned rank = sec->partition * RF_PARTITION;
 
   // We want to put section specified by -T option first, so we
   // can start assigning VA starting from them later.
   if (config->sectionStartMap.count(sec->name))
     return rank;
   rank |= RF_NOT_ADDR_SET;
 
   // Allocatable sections go first to reduce the total PT_LOAD size and
   // so debug info doesn't change addresses in actual code.
   if (!(sec->flags & SHF_ALLOC))
     return rank | RF_NOT_ALLOC;
 
   if (sec->type == SHT_LLVM_PART_EHDR)
     return rank;
   rank |= RF_NOT_PART_EHDR;
 
   if (sec->type == SHT_LLVM_PART_PHDR)
     return rank;
   rank |= RF_NOT_PART_PHDR;
 
   // Put .interp first because some loaders want to see that section
   // on the first page of the executable file when loaded into memory.
   if (sec->name == ".interp")
     return rank;
   rank |= RF_NOT_INTERP;
 
   // Put .note sections (which make up one PT_NOTE) at the beginning so that
   // they are likely to be included in a core file even if core file size is
   // limited. In particular, we want a .note.gnu.build-id and a .note.tag to be
   // included in a core to match core files with executables.
   if (sec->type == SHT_NOTE)
     return rank;
   rank |= RF_NOT_NOTE;
 
   // Sort sections based on their access permission in the following
   // order: R, RX, RWX, RW.  This order is based on the following
   // considerations:
   // * Read-only sections come first such that they go in the
   //   PT_LOAD covering the program headers at the start of the file.
   // * Read-only, executable sections come next.
   // * Writable, executable sections follow such that .plt on
   //   architectures where it needs to be writable will be placed
   //   between .text and .data.
   // * Writable sections come last, such that .bss lands at the very
   //   end of the last PT_LOAD.
   bool isExec = sec->flags & SHF_EXECINSTR;
   bool isWrite = sec->flags & SHF_WRITE;
 
   if (isExec) {
     if (isWrite)
       rank |= RF_EXEC_WRITE;
     else
       rank |= RF_EXEC;
   } else if (isWrite) {
     rank |= RF_WRITE;
   } else if (sec->type == SHT_PROGBITS) {
     // Make non-executable and non-writable PROGBITS sections (e.g .rodata
     // .eh_frame) closer to .text. They likely contain PC or GOT relative
     // relocations and there could be relocation overflow if other huge sections
     // (.dynstr .dynsym) were placed in between.
     rank |= RF_RODATA;
   }
 
   // Place RelRo sections first. After considering SHT_NOBITS below, the
   // ordering is PT_LOAD(PT_GNU_RELRO(.data.rel.ro .bss.rel.ro) | .data .bss),
   // where | marks where page alignment happens. An alternative ordering is
   // PT_LOAD(.data | PT_GNU_RELRO( .data.rel.ro .bss.rel.ro) | .bss), but it may
   // waste more bytes due to 2 alignment places.
   if (!isRelroSection(sec))
     rank |= RF_NOT_RELRO;
 
   // If we got here we know that both A and B are in the same PT_LOAD.
 
   // The TLS initialization block needs to be a single contiguous block in a R/W
   // PT_LOAD, so stick TLS sections directly before the other RelRo R/W
   // sections. Since p_filesz can be less than p_memsz, place NOBITS sections
   // after PROGBITS.
   if (!(sec->flags & SHF_TLS))
     rank |= RF_NOT_TLS;
 
   // Within TLS sections, or within other RelRo sections, or within non-RelRo
   // sections, place non-NOBITS sections first.
   if (sec->type == SHT_NOBITS)
     rank |= RF_BSS;
 
   // Some architectures have additional ordering restrictions for sections
   // within the same PT_LOAD.
   if (config->emachine == EM_PPC64) {
     // PPC64 has a number of special SHT_PROGBITS+SHF_ALLOC+SHF_WRITE sections
     // that we would like to make sure appear is a specific order to maximize
     // their coverage by a single signed 16-bit offset from the TOC base
     // pointer. Conversely, the special .tocbss section should be first among
     // all SHT_NOBITS sections. This will put it next to the loaded special
     // PPC64 sections (and, thus, within reach of the TOC base pointer).
     StringRef name = sec->name;
     if (name != ".tocbss")
       rank |= RF_PPC_NOT_TOCBSS;
 
     if (name == ".toc1")
       rank |= RF_PPC_TOCL;
 
     if (name == ".toc")
       rank |= RF_PPC_TOC;
 
     if (name == ".got")
       rank |= RF_PPC_GOT;
 
     if (name == ".branch_lt")
       rank |= RF_PPC_BRANCH_LT;
   }
 
   if (config->emachine == EM_MIPS) {
     // All sections with SHF_MIPS_GPREL flag should be grouped together
     // because data in these sections is addressable with a gp relative address.
     if (sec->flags & SHF_MIPS_GPREL)
       rank |= RF_MIPS_GPREL;
 
     if (sec->name != ".got")
       rank |= RF_MIPS_NOT_GOT;
   }
 
   return rank;
 }
 
 static bool compareSections(const BaseCommand *aCmd, const BaseCommand *bCmd) {
   const OutputSection *a = cast<OutputSection>(aCmd);
   const OutputSection *b = cast<OutputSection>(bCmd);
 
   if (a->sortRank != b->sortRank)
     return a->sortRank < b->sortRank;
 
   if (!(a->sortRank & RF_NOT_ADDR_SET))
     return config->sectionStartMap.lookup(a->name) <
            config->sectionStartMap.lookup(b->name);
   return false;
 }
 
 void PhdrEntry::add(OutputSection *sec) {
   lastSec = sec;
   if (!firstSec)
     firstSec = sec;
   p_align = std::max(p_align, sec->alignment);
   if (p_type == PT_LOAD)
     sec->ptLoad = this;
 }
 
 // The beginning and the ending of .rel[a].plt section are marked
 // with __rel[a]_iplt_{start,end} symbols if it is a statically linked
 // executable. The runtime needs these symbols in order to resolve
 // all IRELATIVE relocs on startup. For dynamic executables, we don't
 // need these symbols, since IRELATIVE relocs are resolved through GOT
 // and PLT. For details, see http://www.airs.com/blog/archives/403.
 template <class ELFT> void Writer<ELFT>::addRelIpltSymbols() {
   if (config->relocatable || needsInterpSection())
     return;
 
   // By default, __rela_iplt_{start,end} belong to a dummy section 0
   // because .rela.plt might be empty and thus removed from output.
   // We'll override Out::elfHeader with In.relaIplt later when we are
   // sure that .rela.plt exists in output.
   ElfSym::relaIpltStart = addOptionalRegular(
       config->isRela ? "__rela_iplt_start" : "__rel_iplt_start",
       Out::elfHeader, 0, STV_HIDDEN, STB_WEAK);
 
   ElfSym::relaIpltEnd = addOptionalRegular(
       config->isRela ? "__rela_iplt_end" : "__rel_iplt_end",
       Out::elfHeader, 0, STV_HIDDEN, STB_WEAK);
 }
 
 template <class ELFT>
 void Writer<ELFT>::forEachRelSec(
     llvm::function_ref<void(InputSectionBase &)> fn) {
   // Scan all relocations. Each relocation goes through a series
   // of tests to determine if it needs special treatment, such as
   // creating GOT, PLT, copy relocations, etc.
   // Note that relocations for non-alloc sections are directly
   // processed by InputSection::relocateNonAlloc.
   for (InputSectionBase *isec : inputSections)
     if (isec->isLive() && isa<InputSection>(isec) && (isec->flags & SHF_ALLOC))
       fn(*isec);
   for (Partition &part : partitions) {
     for (EhInputSection *es : part.ehFrame->sections)
       fn(*es);
     if (part.armExidx && part.armExidx->isLive())
       for (InputSection *ex : part.armExidx->exidxSections)
         fn(*ex);
   }
 }
 
 // This function generates assignments for predefined symbols (e.g. _end or
 // _etext) and inserts them into the commands sequence to be processed at the
 // appropriate time. This ensures that the value is going to be correct by the
 // time any references to these symbols are processed and is equivalent to
 // defining these symbols explicitly in the linker script.
 template <class ELFT> void Writer<ELFT>::setReservedSymbolSections() {
   if (ElfSym::globalOffsetTable) {
     // The _GLOBAL_OFFSET_TABLE_ symbol is defined by target convention usually
     // to the start of the .got or .got.plt section.
     InputSection *gotSection = in.gotPlt;
     if (!target->gotBaseSymInGotPlt)
       gotSection = in.mipsGot ? cast<InputSection>(in.mipsGot)
                               : cast<InputSection>(in.got);
     ElfSym::globalOffsetTable->section = gotSection;
   }
 
   // .rela_iplt_{start,end} mark the start and the end of in.relaIplt.
   if (ElfSym::relaIpltStart && in.relaIplt->isNeeded()) {
     ElfSym::relaIpltStart->section = in.relaIplt;
     ElfSym::relaIpltEnd->section = in.relaIplt;
     ElfSym::relaIpltEnd->value = in.relaIplt->getSize();
   }
 
   PhdrEntry *last = nullptr;
   PhdrEntry *lastRO = nullptr;
 
   for (Partition &part : partitions) {
     for (PhdrEntry *p : part.phdrs) {
       if (p->p_type != PT_LOAD)
         continue;
       last = p;
       if (!(p->p_flags & PF_W))
         lastRO = p;
     }
   }
 
   if (lastRO) {
     // _etext is the first location after the last read-only loadable segment.
     if (ElfSym::etext1)
       ElfSym::etext1->section = lastRO->lastSec;
     if (ElfSym::etext2)
       ElfSym::etext2->section = lastRO->lastSec;
   }
 
   if (last) {
     // _edata points to the end of the last mapped initialized section.
     OutputSection *edata = nullptr;
     for (OutputSection *os : outputSections) {
       if (os->type != SHT_NOBITS)
         edata = os;
       if (os == last->lastSec)
         break;
     }
 
     if (ElfSym::edata1)
       ElfSym::edata1->section = edata;
     if (ElfSym::edata2)
       ElfSym::edata2->section = edata;
 
     // _end is the first location after the uninitialized data region.
     if (ElfSym::end1)
       ElfSym::end1->section = last->lastSec;
     if (ElfSym::end2)
       ElfSym::end2->section = last->lastSec;
   }
 
   if (ElfSym::bss)
     ElfSym::bss->section = findSection(".bss");
 
   // Setup MIPS _gp_disp/__gnu_local_gp symbols which should
   // be equal to the _gp symbol's value.
   if (ElfSym::mipsGp) {
     // Find GP-relative section with the lowest address
     // and use this address to calculate default _gp value.
     for (OutputSection *os : outputSections) {
       if (os->flags & SHF_MIPS_GPREL) {
         ElfSym::mipsGp->section = os;
         ElfSym::mipsGp->value = 0x7ff0;
         break;
       }
     }
   }
 }
 
 // We want to find how similar two ranks are.
 // The more branches in getSectionRank that match, the more similar they are.
 // Since each branch corresponds to a bit flag, we can just use
 // countLeadingZeros.
 static int getRankProximityAux(OutputSection *a, OutputSection *b) {
   return countLeadingZeros(a->sortRank ^ b->sortRank);
 }
 
 static int getRankProximity(OutputSection *a, BaseCommand *b) {
   auto *sec = dyn_cast<OutputSection>(b);
   return (sec && sec->hasInputSections) ? getRankProximityAux(a, sec) : -1;
 }
 
 // When placing orphan sections, we want to place them after symbol assignments
 // so that an orphan after
 //   begin_foo = .;
 //   foo : { *(foo) }
 //   end_foo = .;
 // doesn't break the intended meaning of the begin/end symbols.
 // We don't want to go over sections since findOrphanPos is the
 // one in charge of deciding the order of the sections.
 // We don't want to go over changes to '.', since doing so in
 //  rx_sec : { *(rx_sec) }
 //  . = ALIGN(0x1000);
 //  /* The RW PT_LOAD starts here*/
 //  rw_sec : { *(rw_sec) }
 // would mean that the RW PT_LOAD would become unaligned.
 static bool shouldSkip(BaseCommand *cmd) {
   if (auto *assign = dyn_cast<SymbolAssignment>(cmd))
     return assign->name != ".";
   return false;
 }
 
 // We want to place orphan sections so that they share as much
 // characteristics with their neighbors as possible. For example, if
 // both are rw, or both are tls.
 static std::vector<BaseCommand *>::iterator
 findOrphanPos(std::vector<BaseCommand *>::iterator b,
               std::vector<BaseCommand *>::iterator e) {
   OutputSection *sec = cast<OutputSection>(*e);
 
   // Find the first element that has as close a rank as possible.
   auto i = std::max_element(b, e, [=](BaseCommand *a, BaseCommand *b) {
     return getRankProximity(sec, a) < getRankProximity(sec, b);
   });
   if (i == e)
     return e;
 
   // Consider all existing sections with the same proximity.
   int proximity = getRankProximity(sec, *i);
   for (; i != e; ++i) {
     auto *curSec = dyn_cast<OutputSection>(*i);
     if (!curSec || !curSec->hasInputSections)
       continue;
     if (getRankProximity(sec, curSec) != proximity ||
         sec->sortRank < curSec->sortRank)
       break;
   }
 
   auto isOutputSecWithInputSections = [](BaseCommand *cmd) {
     auto *os = dyn_cast<OutputSection>(cmd);
     return os && os->hasInputSections;
   };
   auto j = std::find_if(llvm::make_reverse_iterator(i),
                         llvm::make_reverse_iterator(b),
                         isOutputSecWithInputSections);
   i = j.base();
 
   // As a special case, if the orphan section is the last section, put
   // it at the very end, past any other commands.
   // This matches bfd's behavior and is convenient when the linker script fully
   // specifies the start of the file, but doesn't care about the end (the non
   // alloc sections for example).
   auto nextSec = std::find_if(i, e, isOutputSecWithInputSections);
   if (nextSec == e)
     return e;
 
   while (i != e && shouldSkip(*i))
     ++i;
   return i;
 }
 
 // Builds section order for handling --symbol-ordering-file.
 static DenseMap<const InputSectionBase *, int> buildSectionOrder() {
   DenseMap<const InputSectionBase *, int> sectionOrder;
   // Use the rarely used option -call-graph-ordering-file to sort sections.
   if (!config->callGraphProfile.empty())
     return computeCallGraphProfileOrder();
 
   if (config->symbolOrderingFile.empty())
     return sectionOrder;
 
   struct SymbolOrderEntry {
     int priority;
     bool present;
   };
 
   // Build a map from symbols to their priorities. Symbols that didn't
   // appear in the symbol ordering file have the lowest priority 0.
   // All explicitly mentioned symbols have negative (higher) priorities.
   DenseMap<StringRef, SymbolOrderEntry> symbolOrder;
   int priority = -config->symbolOrderingFile.size();
   for (StringRef s : config->symbolOrderingFile)
     symbolOrder.insert({s, {priority++, false}});
 
   // Build a map from sections to their priorities.
   auto addSym = [&](Symbol &sym) {
     auto it = symbolOrder.find(sym.getName());
     if (it == symbolOrder.end())
       return;
     SymbolOrderEntry &ent = it->second;
     ent.present = true;
 
     maybeWarnUnorderableSymbol(&sym);
 
     if (auto *d = dyn_cast<Defined>(&sym)) {
       if (auto *sec = dyn_cast_or_null<InputSectionBase>(d->section)) {
         int &priority = sectionOrder[cast<InputSectionBase>(sec->repl)];
         priority = std::min(priority, ent.priority);
       }
     }
   };
 
   // We want both global and local symbols. We get the global ones from the
   // symbol table and iterate the object files for the local ones.
   for (Symbol *sym : symtab->symbols())
     if (!sym->isLazy())
       addSym(*sym);
 
   for (InputFile *file : objectFiles)
     for (Symbol *sym : file->getSymbols())
       if (sym->isLocal())
         addSym(*sym);
 
   if (config->warnSymbolOrdering)
     for (auto orderEntry : symbolOrder)
       if (!orderEntry.second.present)
         warn("symbol ordering file: no such symbol: " + orderEntry.first);
 
   return sectionOrder;
 }
 
 // Sorts the sections in ISD according to the provided section order.
 static void
 sortISDBySectionOrder(InputSectionDescription *isd,
                       const DenseMap<const InputSectionBase *, int> &order) {
   std::vector<InputSection *> unorderedSections;
   std::vector<std::pair<InputSection *, int>> orderedSections;
   uint64_t unorderedSize = 0;
 
   for (InputSection *isec : isd->sections) {
     auto i = order.find(isec);
     if (i == order.end()) {
       unorderedSections.push_back(isec);
       unorderedSize += isec->getSize();
       continue;
     }
     orderedSections.push_back({isec, i->second});
   }
   llvm::sort(orderedSections, llvm::less_second());
 
   // Find an insertion point for the ordered section list in the unordered
   // section list. On targets with limited-range branches, this is the mid-point
   // of the unordered section list. This decreases the likelihood that a range
   // extension thunk will be needed to enter or exit the ordered region. If the
   // ordered section list is a list of hot functions, we can generally expect
   // the ordered functions to be called more often than the unordered functions,
   // making it more likely that any particular call will be within range, and
   // therefore reducing the number of thunks required.
   //
   // For example, imagine that you have 8MB of hot code and 32MB of cold code.
   // If the layout is:
   //
   // 8MB hot
   // 32MB cold
   //
   // only the first 8-16MB of the cold code (depending on which hot function it
   // is actually calling) can call the hot code without a range extension thunk.
   // However, if we use this layout:
   //
   // 16MB cold
   // 8MB hot
   // 16MB cold
   //
   // both the last 8-16MB of the first block of cold code and the first 8-16MB
   // of the second block of cold code can call the hot code without a thunk. So
   // we effectively double the amount of code that could potentially call into
   // the hot code without a thunk.
   size_t insPt = 0;
   if (target->getThunkSectionSpacing() && !orderedSections.empty()) {
     uint64_t unorderedPos = 0;
     for (; insPt != unorderedSections.size(); ++insPt) {
       unorderedPos += unorderedSections[insPt]->getSize();
       if (unorderedPos > unorderedSize / 2)
         break;
     }
   }
 
   isd->sections.clear();
   for (InputSection *isec : makeArrayRef(unorderedSections).slice(0, insPt))
     isd->sections.push_back(isec);
   for (std::pair<InputSection *, int> p : orderedSections)
     isd->sections.push_back(p.first);
   for (InputSection *isec : makeArrayRef(unorderedSections).slice(insPt))
     isd->sections.push_back(isec);
 }
 
 static void sortSection(OutputSection *sec,
                         const DenseMap<const InputSectionBase *, int> &order) {
   StringRef name = sec->name;
 
   // Sort input sections by section name suffixes for
   // __attribute__((init_priority(N))).
   if (name == ".init_array" || name == ".fini_array") {
     if (!script->hasSectionsCommand)
       sec->sortInitFini();
     return;
   }
 
   // Sort input sections by the special rule for .ctors and .dtors.
   if (name == ".ctors" || name == ".dtors") {
     if (!script->hasSectionsCommand)
       sec->sortCtorsDtors();
     return;
   }
 
   // Never sort these.
   if (name == ".init" || name == ".fini")
     return;
 
   // .toc is allocated just after .got and is accessed using GOT-relative
   // relocations. Object files compiled with small code model have an
   // addressable range of [.got, .got + 0xFFFC] for GOT-relative relocations.
   // To reduce the risk of relocation overflow, .toc contents are sorted so that
   // sections having smaller relocation offsets are at beginning of .toc
   if (config->emachine == EM_PPC64 && name == ".toc") {
     if (script->hasSectionsCommand)
       return;
     assert(sec->sectionCommands.size() == 1);
     auto *isd = cast<InputSectionDescription>(sec->sectionCommands[0]);
     llvm::stable_sort(isd->sections,
                       [](const InputSection *a, const InputSection *b) -> bool {
                         return a->file->ppc64SmallCodeModelTocRelocs &&
                                !b->file->ppc64SmallCodeModelTocRelocs;
                       });
     return;
   }
 
   // Sort input sections by priority using the list provided
   // by --symbol-ordering-file.
   if (!order.empty())
     for (BaseCommand *b : sec->sectionCommands)
       if (auto *isd = dyn_cast<InputSectionDescription>(b))
         sortISDBySectionOrder(isd, order);
 }
 
 // If no layout was provided by linker script, we want to apply default
 // sorting for special input sections. This also handles --symbol-ordering-file.
 template <class ELFT> void Writer<ELFT>::sortInputSections() {
   // Build the order once since it is expensive.
   DenseMap<const InputSectionBase *, int> order = buildSectionOrder();
   for (BaseCommand *base : script->sectionCommands)
     if (auto *sec = dyn_cast<OutputSection>(base))
       sortSection(sec, order);
 }
 
 template <class ELFT> void Writer<ELFT>::sortSections() {
   script->adjustSectionsBeforeSorting();
 
   // Don't sort if using -r. It is not necessary and we want to preserve the
   // relative order for SHF_LINK_ORDER sections.
   if (config->relocatable)
     return;
 
   sortInputSections();
 
   for (BaseCommand *base : script->sectionCommands) {
     auto *os = dyn_cast<OutputSection>(base);
     if (!os)
       continue;
     os->sortRank = getSectionRank(os);
 
     // We want to assign rude approximation values to outSecOff fields
     // to know the relative order of the input sections. We use it for
     // sorting SHF_LINK_ORDER sections. See resolveShfLinkOrder().
     uint64_t i = 0;
     for (InputSection *sec : getInputSections(os))
       sec->outSecOff = i++;
   }
 
   if (!script->hasSectionsCommand) {
     // We know that all the OutputSections are contiguous in this case.
     auto isSection = [](BaseCommand *base) { return isa<OutputSection>(base); };
     std::stable_sort(
         llvm::find_if(script->sectionCommands, isSection),
         llvm::find_if(llvm::reverse(script->sectionCommands), isSection).base(),
         compareSections);
     return;
   }
 
   // Orphan sections are sections present in the input files which are
   // not explicitly placed into the output file by the linker script.
   //
   // The sections in the linker script are already in the correct
   // order. We have to figuere out where to insert the orphan
   // sections.
   //
   // The order of the sections in the script is arbitrary and may not agree with
   // compareSections. This means that we cannot easily define a strict weak
   // ordering. To see why, consider a comparison of a section in the script and
   // one not in the script. We have a two simple options:
   // * Make them equivalent (a is not less than b, and b is not less than a).
   //   The problem is then that equivalence has to be transitive and we can
   //   have sections a, b and c with only b in a script and a less than c
   //   which breaks this property.
   // * Use compareSectionsNonScript. Given that the script order doesn't have
   //   to match, we can end up with sections a, b, c, d where b and c are in the
   //   script and c is compareSectionsNonScript less than b. In which case d
   //   can be equivalent to c, a to b and d < a. As a concrete example:
   //   .a (rx) # not in script
   //   .b (rx) # in script
   //   .c (ro) # in script
   //   .d (ro) # not in script
   //
   // The way we define an order then is:
   // *  Sort only the orphan sections. They are in the end right now.
   // *  Move each orphan section to its preferred position. We try
   //    to put each section in the last position where it can share
   //    a PT_LOAD.
   //
   // There is some ambiguity as to where exactly a new entry should be
   // inserted, because Commands contains not only output section
   // commands but also other types of commands such as symbol assignment
   // expressions. There's no correct answer here due to the lack of the
   // formal specification of the linker script. We use heuristics to
   // determine whether a new output command should be added before or
   // after another commands. For the details, look at shouldSkip
   // function.
 
   auto i = script->sectionCommands.begin();
   auto e = script->sectionCommands.end();
   auto nonScriptI = std::find_if(i, e, [](BaseCommand *base) {
     if (auto *sec = dyn_cast<OutputSection>(base))
       return sec->sectionIndex == UINT32_MAX;
     return false;
   });
 
   // Sort the orphan sections.
   std::stable_sort(nonScriptI, e, compareSections);
 
   // As a horrible special case, skip the first . assignment if it is before any
   // section. We do this because it is common to set a load address by starting
   // the script with ". = 0xabcd" and the expectation is that every section is
   // after that.
   auto firstSectionOrDotAssignment =
       std::find_if(i, e, [](BaseCommand *cmd) { return !shouldSkip(cmd); });
   if (firstSectionOrDotAssignment != e &&
       isa<SymbolAssignment>(**firstSectionOrDotAssignment))
     ++firstSectionOrDotAssignment;
   i = firstSectionOrDotAssignment;
 
   while (nonScriptI != e) {
     auto pos = findOrphanPos(i, nonScriptI);
     OutputSection *orphan = cast<OutputSection>(*nonScriptI);
 
     // As an optimization, find all sections with the same sort rank
     // and insert them with one rotate.
     unsigned rank = orphan->sortRank;
     auto end = std::find_if(nonScriptI + 1, e, [=](BaseCommand *cmd) {
       return cast<OutputSection>(cmd)->sortRank != rank;
     });
     std::rotate(pos, nonScriptI, end);
     nonScriptI = end;
   }
 
   script->adjustSectionsAfterSorting();
 }
 
 static bool compareByFilePosition(InputSection *a, InputSection *b) {
   InputSection *la = a->getLinkOrderDep();
   InputSection *lb = b->getLinkOrderDep();
   OutputSection *aOut = la->getParent();
   OutputSection *bOut = lb->getParent();
 
   if (aOut != bOut)
     return aOut->sectionIndex < bOut->sectionIndex;
   return la->outSecOff < lb->outSecOff;
 }
 
 template <class ELFT> void Writer<ELFT>::resolveShfLinkOrder() {
   for (OutputSection *sec : outputSections) {
     if (!(sec->flags & SHF_LINK_ORDER))
       continue;
 
     // The ARM.exidx section use SHF_LINK_ORDER, but we have consolidated
     // this processing inside the ARMExidxsyntheticsection::finalizeContents().
     if (!config->relocatable && config->emachine == EM_ARM &&
         sec->type == SHT_ARM_EXIDX)
       continue;
 
     // Link order may be distributed across several InputSectionDescriptions
     // but sort must consider them all at once.
     std::vector<InputSection **> scriptSections;
     std::vector<InputSection *> sections;
     for (BaseCommand *base : sec->sectionCommands) {
       if (auto *isd = dyn_cast<InputSectionDescription>(base)) {
         for (InputSection *&isec : isd->sections) {
           scriptSections.push_back(&isec);
           sections.push_back(isec);
 
           InputSection *link = isec->getLinkOrderDep();
           if (!link->getParent())
             error(toString(isec) + ": sh_link points to discarded section " +
                   toString(link));
         }
       }
     }
 
     if (errorCount())
       continue;
 
     llvm::stable_sort(sections, compareByFilePosition);
 
     for (int i = 0, n = sections.size(); i < n; ++i)
       *scriptSections[i] = sections[i];
   }
 }
 
 // We need to generate and finalize the content that depends on the address of
 // InputSections. As the generation of the content may also alter InputSection
 // addresses we must converge to a fixed point. We do that here. See the comment
 // in Writer<ELFT>::finalizeSections().
 template <class ELFT> void Writer<ELFT>::finalizeAddressDependentContent() {
   ThunkCreator tc;
   AArch64Err843419Patcher a64p;
   ARMErr657417Patcher a32p;
   script->assignAddresses();
 
   int assignPasses = 0;
   for (;;) {
     bool changed = target->needsThunks && tc.createThunks(outputSections);
 
     // With Thunk Size much smaller than branch range we expect to
     // converge quickly; if we get to 10 something has gone wrong.
     if (changed && tc.pass >= 10) {
       error("thunk creation not converged");
       break;
     }
 
     if (config->fixCortexA53Errata843419) {
       if (changed)
         script->assignAddresses();
       changed |= a64p.createFixes();
     }
     if (config->fixCortexA8) {
       if (changed)
         script->assignAddresses();
       changed |= a32p.createFixes();
     }
 
     if (in.mipsGot)
       in.mipsGot->updateAllocSize();
 
     for (Partition &part : partitions) {
       changed |= part.relaDyn->updateAllocSize();
       if (part.relrDyn)
         changed |= part.relrDyn->updateAllocSize();
     }
 
     const Defined *changedSym = script->assignAddresses();
     if (!changed) {
       // Some symbols may be dependent on section addresses. When we break the
       // loop, the symbol values are finalized because a previous
       // assignAddresses() finalized section addresses.
       if (!changedSym)
         break;
       if (++assignPasses == 5) {
         errorOrWarn("assignment to symbol " + toString(*changedSym) +
                     " does not converge");
         break;
       }
     }
   }
 }
 
 static void finalizeSynthetic(SyntheticSection *sec) {
   if (sec && sec->isNeeded() && sec->getParent())
     sec->finalizeContents();
 }
 
 // In order to allow users to manipulate linker-synthesized sections,
 // we had to add synthetic sections to the input section list early,
 // even before we make decisions whether they are needed. This allows
 // users to write scripts like this: ".mygot : { .got }".
 //
 // Doing it has an unintended side effects. If it turns out that we
 // don't need a .got (for example) at all because there's no
 // relocation that needs a .got, we don't want to emit .got.
 //
 // To deal with the above problem, this function is called after
 // scanRelocations is called to remove synthetic sections that turn
 // out to be empty.
 static void removeUnusedSyntheticSections() {
   // All input synthetic sections that can be empty are placed after
   // all regular ones. We iterate over them all and exit at first
   // non-synthetic.
   for (InputSectionBase *s : llvm::reverse(inputSections)) {
     SyntheticSection *ss = dyn_cast<SyntheticSection>(s);
     if (!ss)
       return;
     OutputSection *os = ss->getParent();
     if (!os || ss->isNeeded())
       continue;
 
     // If we reach here, then SS is an unused synthetic section and we want to
     // remove it from corresponding input section description of output section.
     for (BaseCommand *b : os->sectionCommands)
       if (auto *isd = dyn_cast<InputSectionDescription>(b))
         llvm::erase_if(isd->sections,
                        [=](InputSection *isec) { return isec == ss; });
   }
 }
 
 // Create output section objects and add them to OutputSections.
 template <class ELFT> void Writer<ELFT>::finalizeSections() {
   Out::preinitArray = findSection(".preinit_array");
   Out::initArray = findSection(".init_array");
   Out::finiArray = findSection(".fini_array");
 
   // The linker needs to define SECNAME_start, SECNAME_end and SECNAME_stop
   // symbols for sections, so that the runtime can get the start and end
   // addresses of each section by section name. Add such symbols.
   if (!config->relocatable) {
     addStartEndSymbols();
     for (BaseCommand *base : script->sectionCommands)
       if (auto *sec = dyn_cast<OutputSection>(base))
         addStartStopSymbols(sec);
   }
 
   // Add _DYNAMIC symbol. Unlike GNU gold, our _DYNAMIC symbol has no type.
   // It should be okay as no one seems to care about the type.
   // Even the author of gold doesn't remember why gold behaves that way.
   // https://sourceware.org/ml/binutils/2002-03/msg00360.html
   if (mainPart->dynamic->parent)
     symtab->addSymbol(Defined{/*file=*/nullptr, "_DYNAMIC", STB_WEAK,
                               STV_HIDDEN, STT_NOTYPE,
                               /*value=*/0, /*size=*/0, mainPart->dynamic});
 
   // Define __rel[a]_iplt_{start,end} symbols if needed.
   addRelIpltSymbols();
 
   // RISC-V's gp can address +/- 2 KiB, set it to .sdata + 0x800. This symbol
   // should only be defined in an executable. If .sdata does not exist, its
   // value/section does not matter but it has to be relative, so set its
   // st_shndx arbitrarily to 1 (Out::elfHeader).
   if (config->emachine == EM_RISCV && !config->shared) {
     OutputSection *sec = findSection(".sdata");
     ElfSym::riscvGlobalPointer =
         addOptionalRegular("__global_pointer$", sec ? sec : Out::elfHeader,
                            0x800, STV_DEFAULT, STB_GLOBAL);
   }
 
   if (config->emachine == EM_X86_64) {
     // On targets that support TLSDESC, _TLS_MODULE_BASE_ is defined in such a
     // way that:
     //
     // 1) Without relaxation: it produces a dynamic TLSDESC relocation that
     // computes 0.
     // 2) With LD->LE relaxation: _TLS_MODULE_BASE_@tpoff = 0 (lowest address in
     // the TLS block).
     //
     // 2) is special cased in @tpoff computation. To satisfy 1), we define it as
     // an absolute symbol of zero. This is different from GNU linkers which
     // define _TLS_MODULE_BASE_ relative to the first TLS section.
     Symbol *s = symtab->find("_TLS_MODULE_BASE_");
     if (s && s->isUndefined()) {
       s->resolve(Defined{/*file=*/nullptr, s->getName(), STB_GLOBAL, STV_HIDDEN,
                          STT_TLS, /*value=*/0, 0,
                          /*section=*/nullptr});
       ElfSym::tlsModuleBase = cast<Defined>(s);
     }
   }
 
   // This responsible for splitting up .eh_frame section into
   // pieces. The relocation scan uses those pieces, so this has to be
   // earlier.
   for (Partition &part : partitions)
     finalizeSynthetic(part.ehFrame);
 
   for (Symbol *sym : symtab->symbols())
     sym->isPreemptible = computeIsPreemptible(*sym);
 
   // Change values of linker-script-defined symbols from placeholders (assigned
   // by declareSymbols) to actual definitions.
   script->processSymbolAssignments();
 
   // Scan relocations. This must be done after every symbol is declared so that
   // we can correctly decide if a dynamic relocation is needed. This is called
   // after processSymbolAssignments() because it needs to know whether a
   // linker-script-defined symbol is absolute.
   if (!config->relocatable) {
     forEachRelSec(scanRelocations<ELFT>);
     reportUndefinedSymbols<ELFT>();
   }
 
   if (in.plt && in.plt->isNeeded())
     in.plt->addSymbols();
   if (in.iplt && in.iplt->isNeeded())
     in.iplt->addSymbols();
 
   if (!config->allowShlibUndefined) {
     // Error on undefined symbols in a shared object, if all of its DT_NEEDED
     // entries are seen. These cases would otherwise lead to runtime errors
     // reported by the dynamic linker.
     //
     // ld.bfd traces all DT_NEEDED to emulate the logic of the dynamic linker to
     // catch more cases. That is too much for us. Our approach resembles the one
     // used in ld.gold, achieves a good balance to be useful but not too smart.
     for (SharedFile *file : sharedFiles)
       file->allNeededIsKnown =
           llvm::all_of(file->dtNeeded, [&](StringRef needed) {
             return symtab->soNames.count(needed);
           });
 
     for (Symbol *sym : symtab->symbols())
       if (sym->isUndefined() && !sym->isWeak())
         if (auto *f = dyn_cast_or_null<SharedFile>(sym->file))
           if (f->allNeededIsKnown)
             error(toString(f) + ": undefined reference to " + toString(*sym));
   }
 
   // Now that we have defined all possible global symbols including linker-
   // synthesized ones. Visit all symbols to give the finishing touches.
   for (Symbol *sym : symtab->symbols()) {
     if (!includeInSymtab(*sym))
       continue;
     if (in.symTab)
       in.symTab->addSymbol(sym);
 
     if (sym->includeInDynsym()) {
       partitions[sym->partition - 1].dynSymTab->addSymbol(sym);
       if (auto *file = dyn_cast_or_null<SharedFile>(sym->file))
         if (file->isNeeded && !sym->isUndefined())
           addVerneed(sym);
     }
   }
 
   // We also need to scan the dynamic relocation tables of the other partitions
   // and add any referenced symbols to the partition's dynsym.
   for (Partition &part : MutableArrayRef<Partition>(partitions).slice(1)) {
     DenseSet<Symbol *> syms;
     for (const SymbolTableEntry &e : part.dynSymTab->getSymbols())
       syms.insert(e.sym);
     for (DynamicReloc &reloc : part.relaDyn->relocs)
       if (reloc.sym && !reloc.useSymVA && syms.insert(reloc.sym).second)
         part.dynSymTab->addSymbol(reloc.sym);
   }
 
   // Do not proceed if there was an undefined symbol.
   if (errorCount())
     return;
 
   if (in.mipsGot)
     in.mipsGot->build();
 
   removeUnusedSyntheticSections();
 
   sortSections();
 
   // Now that we have the final list, create a list of all the
   // OutputSections for convenience.
   for (BaseCommand *base : script->sectionCommands)
     if (auto *sec = dyn_cast<OutputSection>(base))
       outputSections.push_back(sec);
 
   // Prefer command line supplied address over other constraints.
   for (OutputSection *sec : outputSections) {
     auto i = config->sectionStartMap.find(sec->name);
     if (i != config->sectionStartMap.end())
       sec->addrExpr = [=] { return i->second; };
   }
 
   // This is a bit of a hack. A value of 0 means undef, so we set it
   // to 1 to make __ehdr_start defined. The section number is not
   // particularly relevant.
   Out::elfHeader->sectionIndex = 1;
 
   for (size_t i = 0, e = outputSections.size(); i != e; ++i) {
     OutputSection *sec = outputSections[i];
     sec->sectionIndex = i + 1;
     sec->shName = in.shStrTab->addString(sec->name);
   }
 
   // Binary and relocatable output does not have PHDRS.
   // The headers have to be created before finalize as that can influence the
   // image base and the dynamic section on mips includes the image base.
   if (!config->relocatable && !config->oFormatBinary) {
     for (Partition &part : partitions) {
       part.phdrs = script->hasPhdrsCommands() ? script->createPhdrs()
                                               : createPhdrs(part);
       if (config->emachine == EM_ARM) {
         // PT_ARM_EXIDX is the ARM EHABI equivalent of PT_GNU_EH_FRAME
         addPhdrForSection(part, SHT_ARM_EXIDX, PT_ARM_EXIDX, PF_R);
       }
       if (config->emachine == EM_MIPS) {
         // Add separate segments for MIPS-specific sections.
         addPhdrForSection(part, SHT_MIPS_REGINFO, PT_MIPS_REGINFO, PF_R);
         addPhdrForSection(part, SHT_MIPS_OPTIONS, PT_MIPS_OPTIONS, PF_R);
         addPhdrForSection(part, SHT_MIPS_ABIFLAGS, PT_MIPS_ABIFLAGS, PF_R);
       }
     }
     Out::programHeaders->size = sizeof(Elf_Phdr) * mainPart->phdrs.size();
 
     // Find the TLS segment. This happens before the section layout loop so that
     // Android relocation packing can look up TLS symbol addresses. We only need
     // to care about the main partition here because all TLS symbols were moved
     // to the main partition (see MarkLive.cpp).
     for (PhdrEntry *p : mainPart->phdrs)
       if (p->p_type == PT_TLS)
         Out::tlsPhdr = p;
   }
 
   // Some symbols are defined in term of program headers. Now that we
   // have the headers, we can find out which sections they point to.
   setReservedSymbolSections();
 
   finalizeSynthetic(in.bss);
   finalizeSynthetic(in.bssRelRo);
   finalizeSynthetic(in.symTabShndx);
   finalizeSynthetic(in.shStrTab);
   finalizeSynthetic(in.strTab);
   finalizeSynthetic(in.got);
   finalizeSynthetic(in.mipsGot);
   finalizeSynthetic(in.igotPlt);
   finalizeSynthetic(in.gotPlt);
   finalizeSynthetic(in.relaIplt);
   finalizeSynthetic(in.relaPlt);
   finalizeSynthetic(in.plt);
   finalizeSynthetic(in.iplt);
   finalizeSynthetic(in.ppc32Got2);
   finalizeSynthetic(in.partIndex);
 
   // Dynamic section must be the last one in this list and dynamic
   // symbol table section (dynSymTab) must be the first one.
   for (Partition &part : partitions) {
     finalizeSynthetic(part.armExidx);
     finalizeSynthetic(part.dynSymTab);
     finalizeSynthetic(part.gnuHashTab);
     finalizeSynthetic(part.hashTab);
     finalizeSynthetic(part.verDef);
     finalizeSynthetic(part.relaDyn);
     finalizeSynthetic(part.relrDyn);
     finalizeSynthetic(part.ehFrameHdr);
     finalizeSynthetic(part.verSym);
     finalizeSynthetic(part.verNeed);
     finalizeSynthetic(part.dynamic);
   }
 
   if (!script->hasSectionsCommand && !config->relocatable)
     fixSectionAlignments();
 
   // SHFLinkOrder processing must be processed after relative section placements are
   // known but before addresses are allocated.
   resolveShfLinkOrder();
   if (errorCount())
     return;
 
   // This is used to:
   // 1) Create "thunks":
   //    Jump instructions in many ISAs have small displacements, and therefore
   //    they cannot jump to arbitrary addresses in memory. For example, RISC-V
   //    JAL instruction can target only +-1 MiB from PC. It is a linker's
   //    responsibility to create and insert small pieces of code between
   //    sections to extend the ranges if jump targets are out of range. Such
   //    code pieces are called "thunks".
   //
   //    We add thunks at this stage. We couldn't do this before this point
   //    because this is the earliest point where we know sizes of sections and
   //    their layouts (that are needed to determine if jump targets are in
   //    range).
   //
   // 2) Update the sections. We need to generate content that depends on the
   //    address of InputSections. For example, MIPS GOT section content or
   //    android packed relocations sections content.
   //
   // 3) Assign the final values for the linker script symbols. Linker scripts
   //    sometimes using forward symbol declarations. We want to set the correct
   //    values. They also might change after adding the thunks.
   finalizeAddressDependentContent();
 
   // finalizeAddressDependentContent may have added local symbols to the static symbol table.
   finalizeSynthetic(in.symTab);
   finalizeSynthetic(in.ppc64LongBranchTarget);
 
   // Fill other section headers. The dynamic table is finalized
   // at the end because some tags like RELSZ depend on result
   // of finalizing other sections.
   for (OutputSection *sec : outputSections)
     sec->finalize();
 }
 
 // Ensure data sections are not mixed with executable sections when
 // -execute-only is used. -execute-only is a feature to make pages executable
 // but not readable, and the feature is currently supported only on AArch64.
 template <class ELFT> void Writer<ELFT>::checkExecuteOnly() {
   if (!config->executeOnly)
     return;
 
   for (OutputSection *os : outputSections)
     if (os->flags & SHF_EXECINSTR)
       for (InputSection *isec : getInputSections(os))
         if (!(isec->flags & SHF_EXECINSTR))
           error("cannot place " + toString(isec) + " into " + toString(os->name) +
                 ": -execute-only does not support intermingling data and code");
 }
 
 // The linker is expected to define SECNAME_start and SECNAME_end
 // symbols for a few sections. This function defines them.
 template <class ELFT> void Writer<ELFT>::addStartEndSymbols() {
   // If a section does not exist, there's ambiguity as to how we
   // define _start and _end symbols for an init/fini section. Since
   // the loader assume that the symbols are always defined, we need to
   // always define them. But what value? The loader iterates over all
   // pointers between _start and _end to run global ctors/dtors, so if
   // the section is empty, their symbol values don't actually matter
   // as long as _start and _end point to the same location.
   //
   // That said, we don't want to set the symbols to 0 (which is
   // probably the simplest value) because that could cause some
   // program to fail to link due to relocation overflow, if their
   // program text is above 2 GiB. We use the address of the .text
   // section instead to prevent that failure.
   //
   // In rare situations, the .text section may not exist. If that's the
   // case, use the image base address as a last resort.
   OutputSection *Default = findSection(".text");
   if (!Default)
     Default = Out::elfHeader;
 
   auto define = [=](StringRef start, StringRef end, OutputSection *os) {
     if (os) {
       addOptionalRegular(start, os, 0);
       addOptionalRegular(end, os, -1);
     } else {
       addOptionalRegular(start, Default, 0);
       addOptionalRegular(end, Default, 0);
     }
   };
 
   define("__preinit_array_start", "__preinit_array_end", Out::preinitArray);
   define("__init_array_start", "__init_array_end", Out::initArray);
   define("__fini_array_start", "__fini_array_end", Out::finiArray);
 
   if (OutputSection *sec = findSection(".ARM.exidx"))
     define("__exidx_start", "__exidx_end", sec);
 }
 
 // If a section name is valid as a C identifier (which is rare because of
 // the leading '.'), linkers are expected to define __start_<secname> and
 // __stop_<secname> symbols. They are at beginning and end of the section,
 // respectively. This is not requested by the ELF standard, but GNU ld and
 // gold provide the feature, and used by many programs.
 template <class ELFT>
 void Writer<ELFT>::addStartStopSymbols(OutputSection *sec) {
   StringRef s = sec->name;
   if (!isValidCIdentifier(s))
     return;
   addOptionalRegular(saver.save("__start_" + s), sec, 0, STV_PROTECTED);
   addOptionalRegular(saver.save("__stop_" + s), sec, -1, STV_PROTECTED);
 }
 
 static bool needsPtLoad(OutputSection *sec) {
   if (!(sec->flags & SHF_ALLOC) || sec->noload)
     return false;
 
   // Don't allocate VA space for TLS NOBITS sections. The PT_TLS PHDR is
   // responsible for allocating space for them, not the PT_LOAD that
   // contains the TLS initialization image.
   if ((sec->flags & SHF_TLS) && sec->type == SHT_NOBITS)
     return false;
   return true;
 }
 
 // Linker scripts are responsible for aligning addresses. Unfortunately, most
 // linker scripts are designed for creating two PT_LOADs only, one RX and one
 // RW. This means that there is no alignment in the RO to RX transition and we
 // cannot create a PT_LOAD there.
 static uint64_t computeFlags(uint64_t flags) {
   if (config->omagic)
     return PF_R | PF_W | PF_X;
   if (config->executeOnly && (flags & PF_X))
     return flags & ~PF_R;
   if (config->singleRoRx && !(flags & PF_W))
     return flags | PF_X;
   return flags;
 }
 
 // Decide which program headers to create and which sections to include in each
 // one.
 template <class ELFT>
 std::vector<PhdrEntry *> Writer<ELFT>::createPhdrs(Partition &part) {
   std::vector<PhdrEntry *> ret;
   auto addHdr = [&](unsigned type, unsigned flags) -> PhdrEntry * {
     ret.push_back(make<PhdrEntry>(type, flags));
     return ret.back();
   };
 
   unsigned partNo = part.getNumber();
   bool isMain = partNo == 1;
 
   // Add the first PT_LOAD segment for regular output sections.
   uint64_t flags = computeFlags(PF_R);
   PhdrEntry *load = nullptr;
 
   // nmagic or omagic output does not have PT_PHDR, PT_INTERP, or the readonly
   // PT_LOAD.
   if (!config->nmagic && !config->omagic) {
     // The first phdr entry is PT_PHDR which describes the program header
     // itself.
     if (isMain)
       addHdr(PT_PHDR, PF_R)->add(Out::programHeaders);
     else
       addHdr(PT_PHDR, PF_R)->add(part.programHeaders->getParent());
 
     // PT_INTERP must be the second entry if exists.
     if (OutputSection *cmd = findSection(".interp", partNo))
       addHdr(PT_INTERP, cmd->getPhdrFlags())->add(cmd);
 
     // Add the headers. We will remove them if they don't fit.
     // In the other partitions the headers are ordinary sections, so they don't
     // need to be added here.
     if (isMain) {
       load = addHdr(PT_LOAD, flags);
       load->add(Out::elfHeader);
       load->add(Out::programHeaders);
     }
   }
 
   // PT_GNU_RELRO includes all sections that should be marked as
   // read-only by dynamic linker after processing relocations.
   // Current dynamic loaders only support one PT_GNU_RELRO PHDR, give
   // an error message if more than one PT_GNU_RELRO PHDR is required.
   PhdrEntry *relRo = make<PhdrEntry>(PT_GNU_RELRO, PF_R);
   bool inRelroPhdr = false;
   OutputSection *relroEnd = nullptr;
   for (OutputSection *sec : outputSections) {
     if (sec->partition != partNo || !needsPtLoad(sec))
       continue;
     if (isRelroSection(sec)) {
       inRelroPhdr = true;
       if (!relroEnd)
         relRo->add(sec);
       else
         error("section: " + sec->name + " is not contiguous with other relro" +
               " sections");
     } else if (inRelroPhdr) {
       inRelroPhdr = false;
       relroEnd = sec;
     }
   }
 
   for (OutputSection *sec : outputSections) {
     if (!(sec->flags & SHF_ALLOC))
       break;
     if (!needsPtLoad(sec))
       continue;
 
     // Normally, sections in partitions other than the current partition are
     // ignored. But partition number 255 is a special case: it contains the
     // partition end marker (.part.end). It needs to be added to the main
     // partition so that a segment is created for it in the main partition,
     // which will cause the dynamic loader to reserve space for the other
     // partitions.
     if (sec->partition != partNo) {
       if (isMain && sec->partition == 255)
         addHdr(PT_LOAD, computeFlags(sec->getPhdrFlags()))->add(sec);
       continue;
     }
 
     // Segments are contiguous memory regions that has the same attributes
     // (e.g. executable or writable). There is one phdr for each segment.
     // Therefore, we need to create a new phdr when the next section has
     // different flags or is loaded at a discontiguous address or memory
     // region using AT or AT> linker script command, respectively. At the same
     // time, we don't want to create a separate load segment for the headers,
     // even if the first output section has an AT or AT> attribute.
     uint64_t newFlags = computeFlags(sec->getPhdrFlags());
     if (!load ||
         ((sec->lmaExpr ||
           (sec->lmaRegion && (sec->lmaRegion != load->firstSec->lmaRegion))) &&
          load->lastSec != Out::programHeaders) ||
         sec->memRegion != load->firstSec->memRegion || flags != newFlags ||
         sec == relroEnd) {
       load = addHdr(PT_LOAD, newFlags);
       flags = newFlags;
     }
 
     load->add(sec);
   }
 
   // Add a TLS segment if any.
   PhdrEntry *tlsHdr = make<PhdrEntry>(PT_TLS, PF_R);
   for (OutputSection *sec : outputSections)
     if (sec->partition == partNo && sec->flags & SHF_TLS)
       tlsHdr->add(sec);
   if (tlsHdr->firstSec)
     ret.push_back(tlsHdr);
 
   // Add an entry for .dynamic.
   if (OutputSection *sec = part.dynamic->getParent())
     addHdr(PT_DYNAMIC, sec->getPhdrFlags())->add(sec);
 
   if (relRo->firstSec)
     ret.push_back(relRo);
 
   // PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
   if (part.ehFrame->isNeeded() && part.ehFrameHdr &&
       part.ehFrame->getParent() && part.ehFrameHdr->getParent())
     addHdr(PT_GNU_EH_FRAME, part.ehFrameHdr->getParent()->getPhdrFlags())
         ->add(part.ehFrameHdr->getParent());
 
   // PT_OPENBSD_RANDOMIZE is an OpenBSD-specific feature. That makes
   // the dynamic linker fill the segment with random data.
   if (OutputSection *cmd = findSection(".openbsd.randomdata", partNo))
     addHdr(PT_OPENBSD_RANDOMIZE, cmd->getPhdrFlags())->add(cmd);
 
   if (config->zGnustack != GnuStackKind::None) {
     // PT_GNU_STACK is a special section to tell the loader to make the
     // pages for the stack non-executable. If you really want an executable
     // stack, you can pass -z execstack, but that's not recommended for
     // security reasons.
     unsigned perm = PF_R | PF_W;
     if (config->zGnustack == GnuStackKind::Exec)
       perm |= PF_X;
     addHdr(PT_GNU_STACK, perm)->p_memsz = config->zStackSize;
   }
 
   // PT_OPENBSD_WXNEEDED is a OpenBSD-specific header to mark the executable
   // is expected to perform W^X violations, such as calling mprotect(2) or
   // mmap(2) with PROT_WRITE | PROT_EXEC, which is prohibited by default on
   // OpenBSD.
   if (config->zWxneeded)
     addHdr(PT_OPENBSD_WXNEEDED, PF_X);
 
   if (OutputSection *cmd = findSection(".note.gnu.property", partNo))
     addHdr(PT_GNU_PROPERTY, PF_R)->add(cmd);
 
   // Create one PT_NOTE per a group of contiguous SHT_NOTE sections with the
   // same alignment.
   PhdrEntry *note = nullptr;
   for (OutputSection *sec : outputSections) {
     if (sec->partition != partNo)
       continue;
     if (sec->type == SHT_NOTE && (sec->flags & SHF_ALLOC)) {
       if (!note || sec->lmaExpr || note->lastSec->alignment != sec->alignment)
         note = addHdr(PT_NOTE, PF_R);
       note->add(sec);
     } else {
       note = nullptr;
     }
   }
   return ret;
 }
 
 template <class ELFT>
 void Writer<ELFT>::addPhdrForSection(Partition &part, unsigned shType,
                                      unsigned pType, unsigned pFlags) {
   unsigned partNo = part.getNumber();
   auto i = llvm::find_if(outputSections, [=](OutputSection *cmd) {
     return cmd->partition == partNo && cmd->type == shType;
   });
   if (i == outputSections.end())
     return;
 
   PhdrEntry *entry = make<PhdrEntry>(pType, pFlags);
   entry->add(*i);
   part.phdrs.push_back(entry);
 }
 
 // Place the first section of each PT_LOAD to a different page (of maxPageSize).
 // This is achieved by assigning an alignment expression to addrExpr of each
 // such section.
 template <class ELFT> void Writer<ELFT>::fixSectionAlignments() {
   const PhdrEntry *prev;
   auto pageAlign = [&](const PhdrEntry *p) {
     OutputSection *cmd = p->firstSec;
     if (cmd && !cmd->addrExpr) {
       // Prefer advancing to align(dot, maxPageSize) + dot%maxPageSize to avoid
       // padding in the file contents.
       //
       // When -z separate-code is used we must not have any overlap in pages
       // between an executable segment and a non-executable segment. We align to
       // the next maximum page size boundary on transitions between executable
       // and non-executable segments.
       //
       // SHT_LLVM_PART_EHDR marks the start of a partition. The partition
       // sections will be extracted to a separate file. Align to the next
       // maximum page size boundary so that we can find the ELF header at the
       // start. We cannot benefit from overlapping p_offset ranges with the
       // previous segment anyway.
       if (config->zSeparate == SeparateSegmentKind::Loadable ||
           (config->zSeparate == SeparateSegmentKind::Code && prev &&
            (prev->p_flags & PF_X) != (p->p_flags & PF_X)) ||
           cmd->type == SHT_LLVM_PART_EHDR)
         cmd->addrExpr = [] {
           return alignTo(script->getDot(), config->maxPageSize);
         };
       // PT_TLS is at the start of the first RW PT_LOAD. If `p` includes PT_TLS,
       // it must be the RW. Align to p_align(PT_TLS) to make sure
       // p_vaddr(PT_LOAD)%p_align(PT_LOAD) = 0. Otherwise, if
       // sh_addralign(.tdata) < sh_addralign(.tbss), we will set p_align(PT_TLS)
       // to sh_addralign(.tbss), while p_vaddr(PT_TLS)=p_vaddr(PT_LOAD) may not
       // be congruent to 0 modulo p_align(PT_TLS).
       //
       // Technically this is not required, but as of 2019, some dynamic loaders
       // don't handle p_vaddr%p_align != 0 correctly, e.g. glibc (i386 and
       // x86-64) doesn't make runtime address congruent to p_vaddr modulo
       // p_align for dynamic TLS blocks (PR/24606), FreeBSD rtld has the same
       // bug, musl (TLS Variant 1 architectures) before 1.1.23 handled TLS
       // blocks correctly. We need to keep the workaround for a while.
       else if (Out::tlsPhdr && Out::tlsPhdr->firstSec == p->firstSec)
         cmd->addrExpr = [] {
           return alignTo(script->getDot(), config->maxPageSize) +
                  alignTo(script->getDot() % config->maxPageSize,
                          Out::tlsPhdr->p_align);
         };
       else
         cmd->addrExpr = [] {
           return alignTo(script->getDot(), config->maxPageSize) +
                  script->getDot() % config->maxPageSize;
         };
     }
   };
 
   for (Partition &part : partitions) {
     prev = nullptr;
     for (const PhdrEntry *p : part.phdrs)
       if (p->p_type == PT_LOAD && p->firstSec) {
         pageAlign(p);
         prev = p;
       }
   }
 }
 
 // Compute an in-file position for a given section. The file offset must be the
 // same with its virtual address modulo the page size, so that the loader can
 // load executables without any address adjustment.
 static uint64_t computeFileOffset(OutputSection *os, uint64_t off) {
   // The first section in a PT_LOAD has to have congruent offset and address
   // modulo the maximum page size.
   if (os->ptLoad && os->ptLoad->firstSec == os)
     return alignTo(off, os->ptLoad->p_align, os->addr);
 
   // File offsets are not significant for .bss sections other than the first one
   // in a PT_LOAD. By convention, we keep section offsets monotonically
   // increasing rather than setting to zero.
    if (os->type == SHT_NOBITS)
      return off;
 
   // If the section is not in a PT_LOAD, we just have to align it.
   if (!os->ptLoad)
     return alignTo(off, os->alignment);
 
   // If two sections share the same PT_LOAD the file offset is calculated
   // using this formula: Off2 = Off1 + (VA2 - VA1).
   OutputSection *first = os->ptLoad->firstSec;
   return first->offset + os->addr - first->addr;
 }
 
 // Set an in-file position to a given section and returns the end position of
 // the section.
 static uint64_t setFileOffset(OutputSection *os, uint64_t off) {
   off = computeFileOffset(os, off);
   os->offset = off;
 
   if (os->type == SHT_NOBITS)
     return off;
   return off + os->size;
 }
 
 template <class ELFT> void Writer<ELFT>::assignFileOffsetsBinary() {
   uint64_t off = 0;
   for (OutputSection *sec : outputSections)
     if (sec->flags & SHF_ALLOC)
       off = setFileOffset(sec, off);
   fileSize = alignTo(off, config->wordsize);
 }
 
 static std::string rangeToString(uint64_t addr, uint64_t len) {
   return "[0x" + utohexstr(addr) + ", 0x" + utohexstr(addr + len - 1) + "]";
 }
 
 // Assign file offsets to output sections.
 template <class ELFT> void Writer<ELFT>::assignFileOffsets() {
   uint64_t off = 0;
   off = setFileOffset(Out::elfHeader, off);
   off = setFileOffset(Out::programHeaders, off);
 
   PhdrEntry *lastRX = nullptr;
   for (Partition &part : partitions)
     for (PhdrEntry *p : part.phdrs)
       if (p->p_type == PT_LOAD && (p->p_flags & PF_X))
         lastRX = p;
 
   for (OutputSection *sec : outputSections) {
     off = setFileOffset(sec, off);
 
     // If this is a last section of the last executable segment and that
     // segment is the last loadable segment, align the offset of the
     // following section to avoid loading non-segments parts of the file.
     if (config->zSeparate != SeparateSegmentKind::None && lastRX &&
         lastRX->lastSec == sec)
       off = alignTo(off, config->commonPageSize);
   }
 
   sectionHeaderOff = alignTo(off, config->wordsize);
   fileSize = sectionHeaderOff + (outputSections.size() + 1) * sizeof(Elf_Shdr);
 
   // Our logic assumes that sections have rising VA within the same segment.
   // With use of linker scripts it is possible to violate this rule and get file
   // offset overlaps or overflows. That should never happen with a valid script
   // which does not move the location counter backwards and usually scripts do
   // not do that. Unfortunately, there are apps in the wild, for example, Linux
   // kernel, which control segment distribution explicitly and move the counter
   // backwards, so we have to allow doing that to support linking them. We
   // perform non-critical checks for overlaps in checkSectionOverlap(), but here
   // we want to prevent file size overflows because it would crash the linker.
   for (OutputSection *sec : outputSections) {
     if (sec->type == SHT_NOBITS)
       continue;
     if ((sec->offset > fileSize) || (sec->offset + sec->size > fileSize))
       error("unable to place section " + sec->name + " at file offset " +
             rangeToString(sec->offset, sec->size) +
             "; check your linker script for overflows");
   }
 }
 
 // Finalize the program headers. We call this function after we assign
 // file offsets and VAs to all sections.
 template <class ELFT> void Writer<ELFT>::setPhdrs(Partition &part) {
   for (PhdrEntry *p : part.phdrs) {
     OutputSection *first = p->firstSec;
     OutputSection *last = p->lastSec;
 
     if (first) {
       p->p_filesz = last->offset - first->offset;
       if (last->type != SHT_NOBITS)
         p->p_filesz += last->size;
 
       p->p_memsz = last->addr + last->size - first->addr;
       p->p_offset = first->offset;
       p->p_vaddr = first->addr;
 
       // File offsets in partitions other than the main partition are relative
       // to the offset of the ELF headers. Perform that adjustment now.
       if (part.elfHeader)
         p->p_offset -= part.elfHeader->getParent()->offset;
 
       if (!p->hasLMA)
         p->p_paddr = first->getLMA();
     }
 
     if (p->p_type == PT_GNU_RELRO) {
       p->p_align = 1;
       // musl/glibc ld.so rounds the size down, so we need to round up
       // to protect the last page. This is a no-op on FreeBSD which always
       // rounds up.
       p->p_memsz = alignTo(p->p_offset + p->p_memsz, config->commonPageSize) -
                    p->p_offset;
     }
   }
 }
 
 // A helper struct for checkSectionOverlap.
 namespace {
 struct SectionOffset {
   OutputSection *sec;
   uint64_t offset;
 };
 } // namespace
 
 // Check whether sections overlap for a specific address range (file offsets,
 // load and virtual addresses).
 static void checkOverlap(StringRef name, std::vector<SectionOffset> &sections,
                          bool isVirtualAddr) {
   llvm::sort(sections, [=](const SectionOffset &a, const SectionOffset &b) {
     return a.offset < b.offset;
   });
 
   // Finding overlap is easy given a vector is sorted by start position.
   // If an element starts before the end of the previous element, they overlap.
   for (size_t i = 1, end = sections.size(); i < end; ++i) {
     SectionOffset a = sections[i - 1];
     SectionOffset b = sections[i];
     if (b.offset >= a.offset + a.sec->size)
       continue;
 
     // If both sections are in OVERLAY we allow the overlapping of virtual
     // addresses, because it is what OVERLAY was designed for.
     if (isVirtualAddr && a.sec->inOverlay && b.sec->inOverlay)
       continue;
 
     errorOrWarn("section " + a.sec->name + " " + name +
                 " range overlaps with " + b.sec->name + "\n>>> " + a.sec->name +
                 " range is " + rangeToString(a.offset, a.sec->size) + "\n>>> " +
                 b.sec->name + " range is " +
                 rangeToString(b.offset, b.sec->size));
   }
 }
 
 // Check for overlapping sections and address overflows.
 //
 // In this function we check that none of the output sections have overlapping
 // file offsets. For SHF_ALLOC sections we also check that the load address
 // ranges and the virtual address ranges don't overlap
 template <class ELFT> void Writer<ELFT>::checkSections() {
   // First, check that section's VAs fit in available address space for target.
   for (OutputSection *os : outputSections)
     if ((os->addr + os->size < os->addr) ||
         (!ELFT::Is64Bits && os->addr + os->size > UINT32_MAX))
       errorOrWarn("section " + os->name + " at 0x" + utohexstr(os->addr) +
                   " of size 0x" + utohexstr(os->size) +
                   " exceeds available address space");
 
   // Check for overlapping file offsets. In this case we need to skip any
   // section marked as SHT_NOBITS. These sections don't actually occupy space in
   // the file so Sec->Offset + Sec->Size can overlap with others. If --oformat
   // binary is specified only add SHF_ALLOC sections are added to the output
   // file so we skip any non-allocated sections in that case.
   std::vector<SectionOffset> fileOffs;
   for (OutputSection *sec : outputSections)
     if (sec->size > 0 && sec->type != SHT_NOBITS &&
         (!config->oFormatBinary || (sec->flags & SHF_ALLOC)))
       fileOffs.push_back({sec, sec->offset});
   checkOverlap("file", fileOffs, false);
 
   // When linking with -r there is no need to check for overlapping virtual/load
   // addresses since those addresses will only be assigned when the final
   // executable/shared object is created.
   if (config->relocatable)
     return;
 
   // Checking for overlapping virtual and load addresses only needs to take
   // into account SHF_ALLOC sections since others will not be loaded.
   // Furthermore, we also need to skip SHF_TLS sections since these will be
   // mapped to other addresses at runtime and can therefore have overlapping
   // ranges in the file.
   std::vector<SectionOffset> vmas;
   for (OutputSection *sec : outputSections)
     if (sec->size > 0 && (sec->flags & SHF_ALLOC) && !(sec->flags & SHF_TLS))
       vmas.push_back({sec, sec->addr});
   checkOverlap("virtual address", vmas, true);
 
   // Finally, check that the load addresses don't overlap. This will usually be
   // the same as the virtual addresses but can be different when using a linker
   // script with AT().
   std::vector<SectionOffset> lmas;
   for (OutputSection *sec : outputSections)
     if (sec->size > 0 && (sec->flags & SHF_ALLOC) && !(sec->flags & SHF_TLS))
       lmas.push_back({sec, sec->getLMA()});
   checkOverlap("load address", lmas, false);
 }
 
 // The entry point address is chosen in the following ways.
 //
 // 1. the '-e' entry command-line option;
 // 2. the ENTRY(symbol) command in a linker control script;
 // 3. the value of the symbol _start, if present;
 // 4. the number represented by the entry symbol, if it is a number;
 // 5. the address of the first byte of the .text section, if present;
 // 6. the address 0.
 static uint64_t getEntryAddr() {
   // Case 1, 2 or 3
   if (Symbol *b = symtab->find(config->entry))
     return b->getVA();
 
   // Case 4
   uint64_t addr;
   if (to_integer(config->entry, addr))
     return addr;
 
   // Case 5
   if (OutputSection *sec = findSection(".text")) {
     if (config->warnMissingEntry)
       warn("cannot find entry symbol " + config->entry + "; defaulting to 0x" +
            utohexstr(sec->addr));
     return sec->addr;
   }
 
   // Case 6
   if (config->warnMissingEntry)
     warn("cannot find entry symbol " + config->entry +
          "; not setting start address");
   return 0;
 }
 
 static uint16_t getELFType() {
   if (config->isPic)
     return ET_DYN;
   if (config->relocatable)
     return ET_REL;
   return ET_EXEC;
 }
 
 template <class ELFT> void Writer<ELFT>::writeHeader() {
   writeEhdr<ELFT>(Out::bufferStart, *mainPart);
   writePhdrs<ELFT>(Out::bufferStart + sizeof(Elf_Ehdr), *mainPart);
 
   auto *eHdr = reinterpret_cast<Elf_Ehdr *>(Out::bufferStart);
   eHdr->e_type = getELFType();
   eHdr->e_entry = getEntryAddr();
   eHdr->e_shoff = sectionHeaderOff;
 
   // Write the section header table.
   //
   // The ELF header can only store numbers up to SHN_LORESERVE in the e_shnum
   // and e_shstrndx fields. When the value of one of these fields exceeds
   // SHN_LORESERVE ELF requires us to put sentinel values in the ELF header and
   // use fields in the section header at index 0 to store
   // the value. The sentinel values and fields are:
   // e_shnum = 0, SHdrs[0].sh_size = number of sections.
   // e_shstrndx = SHN_XINDEX, SHdrs[0].sh_link = .shstrtab section index.
   auto *sHdrs = reinterpret_cast<Elf_Shdr *>(Out::bufferStart + eHdr->e_shoff);
   size_t num = outputSections.size() + 1;
   if (num >= SHN_LORESERVE)
     sHdrs->sh_size = num;
   else
     eHdr->e_shnum = num;
 
   uint32_t strTabIndex = in.shStrTab->getParent()->sectionIndex;
   if (strTabIndex >= SHN_LORESERVE) {
     sHdrs->sh_link = strTabIndex;
     eHdr->e_shstrndx = SHN_XINDEX;
   } else {
     eHdr->e_shstrndx = strTabIndex;
   }
 
   for (OutputSection *sec : outputSections)
     sec->writeHeaderTo<ELFT>(++sHdrs);
 }
 
 // Open a result file.
 template <class ELFT> void Writer<ELFT>::openFile() {
   uint64_t maxSize = config->is64 ? INT64_MAX : UINT32_MAX;
   if (fileSize != size_t(fileSize) || maxSize < fileSize) {
     error("output file too large: " + Twine(fileSize) + " bytes");
     return;
   }
 
   unlinkAsync(config->outputFile);
   unsigned flags = 0;
   if (!config->relocatable)
     flags |= FileOutputBuffer::F_executable;
   if (!config->mmapOutputFile)
     flags |= FileOutputBuffer::F_no_mmap;
   Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
       FileOutputBuffer::create(config->outputFile, fileSize, flags);
 
   if (!bufferOrErr) {
     error("failed to open " + config->outputFile + ": " +
           llvm::toString(bufferOrErr.takeError()));
     return;
   }
   buffer = std::move(*bufferOrErr);
   Out::bufferStart = buffer->getBufferStart();
 }
 
 template <class ELFT> void Writer<ELFT>::writeSectionsBinary() {
   for (OutputSection *sec : outputSections)
     if (sec->flags & SHF_ALLOC)
       sec->writeTo<ELFT>(Out::bufferStart + sec->offset);
 }
 
 static void fillTrap(uint8_t *i, uint8_t *end) {
   for (; i + 4 <= end; i += 4)
     memcpy(i, &target->trapInstr, 4);
 }
 
 // Fill the last page of executable segments with trap instructions
 // instead of leaving them as zero. Even though it is not required by any
 // standard, it is in general a good thing to do for security reasons.
 //
 // We'll leave other pages in segments as-is because the rest will be
 // overwritten by output sections.
 template <class ELFT> void Writer<ELFT>::writeTrapInstr() {
   for (Partition &part : partitions) {
     // Fill the last page.
     for (PhdrEntry *p : part.phdrs)
       if (p->p_type == PT_LOAD && (p->p_flags & PF_X))
         fillTrap(Out::bufferStart + alignDown(p->firstSec->offset + p->p_filesz,
                                               config->commonPageSize),
                  Out::bufferStart + alignTo(p->firstSec->offset + p->p_filesz,
                                             config->commonPageSize));
 
     // Round up the file size of the last segment to the page boundary iff it is
     // an executable segment to ensure that other tools don't accidentally
     // trim the instruction padding (e.g. when stripping the file).
     PhdrEntry *last = nullptr;
     for (PhdrEntry *p : part.phdrs)
       if (p->p_type == PT_LOAD)
         last = p;
 
     if (last && (last->p_flags & PF_X))
       last->p_memsz = last->p_filesz =
           alignTo(last->p_filesz, config->commonPageSize);
   }
 }
 
 // Write section contents to a mmap'ed file.
 template <class ELFT> void Writer<ELFT>::writeSections() {
   // In -r or -emit-relocs mode, write the relocation sections first as in
   // ELf_Rel targets we might find out that we need to modify the relocated
   // section while doing it.
   for (OutputSection *sec : outputSections)
     if (sec->type == SHT_REL || sec->type == SHT_RELA)
       sec->writeTo<ELFT>(Out::bufferStart + sec->offset);
 
   for (OutputSection *sec : outputSections)
     if (sec->type != SHT_REL && sec->type != SHT_RELA)
       sec->writeTo<ELFT>(Out::bufferStart + sec->offset);
 }
 
 // Split one uint8 array into small pieces of uint8 arrays.
 static std::vector<ArrayRef<uint8_t>> split(ArrayRef<uint8_t> arr,
                                             size_t chunkSize) {
   std::vector<ArrayRef<uint8_t>> ret;
   while (arr.size() > chunkSize) {
     ret.push_back(arr.take_front(chunkSize));
     arr = arr.drop_front(chunkSize);
   }
   if (!arr.empty())
     ret.push_back(arr);
   return ret;
 }
 
 // Computes a hash value of Data using a given hash function.
 // In order to utilize multiple cores, we first split data into 1MB
 // chunks, compute a hash for each chunk, and then compute a hash value
 // of the hash values.
 static void
 computeHash(llvm::MutableArrayRef<uint8_t> hashBuf,
             llvm::ArrayRef<uint8_t> data,
             std::function<void(uint8_t *dest, ArrayRef<uint8_t> arr)> hashFn) {
   std::vector<ArrayRef<uint8_t>> chunks = split(data, 1024 * 1024);
   std::vector<uint8_t> hashes(chunks.size() * hashBuf.size());
 
   // Compute hash values.
   parallelForEachN(0, chunks.size(), [&](size_t i) {
     hashFn(hashes.data() + i * hashBuf.size(), chunks[i]);
   });
 
   // Write to the final output buffer.
   hashFn(hashBuf.data(), hashes);
 }
 
 template <class ELFT> void Writer<ELFT>::writeBuildId() {
   if (!mainPart->buildId || !mainPart->buildId->getParent())
     return;
 
   if (config->buildId == BuildIdKind::Hexstring) {
     for (Partition &part : partitions)
       part.buildId->writeBuildId(config->buildIdVector);
     return;
   }
 
   // Compute a hash of all sections of the output file.
   size_t hashSize = mainPart->buildId->hashSize;
   std::vector<uint8_t> buildId(hashSize);
   llvm::ArrayRef<uint8_t> buf{Out::bufferStart, size_t(fileSize)};
 
   switch (config->buildId) {
   case BuildIdKind::Fast:
     computeHash(buildId, buf, [](uint8_t *dest, ArrayRef<uint8_t> arr) {
       write64le(dest, xxHash64(arr));
     });
     break;
   case BuildIdKind::Md5:
     computeHash(buildId, buf, [&](uint8_t *dest, ArrayRef<uint8_t> arr) {
       memcpy(dest, MD5::hash(arr).data(), hashSize);
     });
     break;
   case BuildIdKind::Sha1:
     computeHash(buildId, buf, [&](uint8_t *dest, ArrayRef<uint8_t> arr) {
       memcpy(dest, SHA1::hash(arr).data(), hashSize);
     });
     break;
   case BuildIdKind::Uuid:
     if (auto ec = llvm::getRandomBytes(buildId.data(), hashSize))
       error("entropy source failure: " + ec.message());
     break;
   default:
     llvm_unreachable("unknown BuildIdKind");
   }
   for (Partition &part : partitions)
     part.buildId->writeBuildId(buildId);
 }
 
 template void createSyntheticSections<ELF32LE>();
 template void createSyntheticSections<ELF32BE>();
 template void createSyntheticSections<ELF64LE>();
 template void createSyntheticSections<ELF64BE>();
 
 template void writeResult<ELF32LE>();
 template void writeResult<ELF32BE>();
 template void writeResult<ELF64LE>();
 template void writeResult<ELF64BE>();
 
 } // namespace elf
 } // namespace lld