Index: contrib/llvm/tools/lld/ELF/InputSection.cpp =================================================================== --- contrib/llvm/tools/lld/ELF/InputSection.cpp +++ contrib/llvm/tools/lld/ELF/InputSection.cpp @@ -610,7 +610,6 @@ case R_ARM_SBREL: return Sym.getVA(A) - getARMStaticBase(Sym); case R_GOT: - case R_GOT_PLT: case R_RELAX_TLS_GD_TO_IE_ABS: return Sym.getGotVA() + A; case R_GOTONLY_PC: @@ -629,7 +628,6 @@ case R_RELAX_TLS_GD_TO_IE_GOT_OFF: return Sym.getGotOffset() + A; case R_AARCH64_GOT_PAGE_PC: - case R_AARCH64_GOT_PAGE_PC_PLT: case R_AARCH64_RELAX_TLS_GD_TO_IE_PAGE_PC: return getAArch64Page(Sym.getGotVA() + A) - getAArch64Page(P); case R_GOT_PC: @@ -679,10 +677,6 @@ uint64_t Val = Sym.isUndefWeak() ? P + A : Sym.getVA(A); return getAArch64Page(Val) - getAArch64Page(P); } - case R_AARCH64_PLT_PAGE_PC: { - uint64_t Val = Sym.isUndefWeak() ? P + A : Sym.getPltVA() + A; - return getAArch64Page(Val) - getAArch64Page(P); - } case R_RISCV_PC_INDIRECT: { if (const Relocation *HiRel = getRISCVPCRelHi20(&Sym, A)) return getRelocTargetVA(File, HiRel->Type, HiRel->Addend, Sym.getVA(), Index: contrib/llvm/tools/lld/ELF/Relocations.h =================================================================== --- contrib/llvm/tools/lld/ELF/Relocations.h +++ contrib/llvm/tools/lld/ELF/Relocations.h @@ -34,19 +34,11 @@ R_ABS, R_ADDEND, R_AARCH64_GOT_PAGE_PC, - // The expression is used for IFUNC support. Describes PC-relative - // address of the memory page of GOT entry. This entry is used for - // a redirection to IPLT. - R_AARCH64_GOT_PAGE_PC_PLT, R_AARCH64_RELAX_TLS_GD_TO_IE_PAGE_PC, R_AARCH64_PAGE_PC, - R_AARCH64_PLT_PAGE_PC, R_AARCH64_TLSDESC_PAGE, R_ARM_SBREL, R_GOT, - // The expression is used for IFUNC support. Evaluates to GOT entry, - // containing redirection to the IPLT. - R_GOT_PLT, R_GOTONLY_PC, R_GOTONLY_PC_FROM_END, R_GOTREL, @@ -155,6 +147,8 @@ template void scanRelocations(InputSectionBase &); +void addIRelativeRelocs(); + class ThunkSection; class Thunk; struct InputSectionDescription; Index: contrib/llvm/tools/lld/ELF/Relocations.cpp =================================================================== --- contrib/llvm/tools/lld/ELF/Relocations.cpp +++ contrib/llvm/tools/lld/ELF/Relocations.cpp @@ -337,8 +337,7 @@ // Returns true if Expr refers a PLT entry. static bool needsPlt(RelExpr Expr) { - return isRelExprOneOf(Expr); + return isRelExprOneOf(Expr); } // Returns true if Expr refers a GOT entry. Note that this function @@ -347,8 +346,7 @@ static bool needsGot(RelExpr Expr) { return isRelExprOneOf(Expr); + R_GOT_PC, R_GOT_FROM_END>(Expr); } // True if this expression is of the form Sym - X, where X is a position in the @@ -356,7 +354,7 @@ static bool isRelExpr(RelExpr Expr) { return isRelExprOneOf(Expr); + R_RELAX_GOT_PC>(Expr); } // Returns true if a given relocation can be computed at link-time. @@ -374,8 +372,8 @@ if (isRelExprOneOf(E)) @@ -387,7 +385,7 @@ // These never do, except if the entire file is position dependent or if // only the low bits are used. - if (E == R_GOT || E == R_GOT_PLT || E == R_PLT || E == R_TLSDESC) + if (E == R_GOT || E == R_PLT || E == R_TLSDESC) return Target->usesOnlyLowPageBits(Type) || !Config->Pic; if (Sym.IsPreemptible) @@ -433,14 +431,8 @@ return R_PPC_CALL_PLT; case R_PC: return R_PLT_PC; - case R_AARCH64_PAGE_PC: - return R_AARCH64_PLT_PAGE_PC; - case R_AARCH64_GOT_PAGE_PC: - return R_AARCH64_GOT_PAGE_PC_PLT; case R_ABS: return R_PLT; - case R_GOT: - return R_GOT_PLT; default: return Expr; } @@ -772,14 +764,7 @@ template static void addGotEntry(Symbol &Sym) { In.Got->addEntry(Sym); - RelExpr Expr; - if (Sym.isTls()) - Expr = R_TLS; - else if (Sym.isGnuIFunc()) - Expr = R_PLT; - else - Expr = R_ABS; - + RelExpr Expr = Sym.isTls() ? R_TLS : R_ABS; uint64_t Off = Sym.getGotOffset(); // If a GOT slot value can be calculated at link-time, which is now, @@ -978,6 +963,15 @@ getLocation(Sec, Sym, Offset)); } +struct IRelativeReloc { + RelType Type; + InputSectionBase *Sec; + uint64_t Offset; + Symbol *Sym; +}; + +static std::vector IRelativeRelocs; + template static void scanReloc(InputSectionBase &Sec, OffsetGetter &GetOffset, RelTy *&I, RelTy *End) { @@ -1009,32 +1003,29 @@ if (isRelExprOneOf(Expr)) return; - // Strenghten or relax relocations. - // - // GNU ifunc symbols must be accessed via PLT because their addresses - // are determined by runtime. + if (Sym.isGnuIFunc() && !Config->ZText && Config->WarnIfuncTextrel) { + warn("using ifunc symbols when text relocations are allowed may produce " + "a binary that will segfault, if the object file is linked with " + "old version of glibc (glibc 2.28 and earlier). If this applies to " + "you, consider recompiling the object files without -fPIC and " + "without -Wl,-z,notext option. Use -no-warn-ifunc-textrel to " + "turn off this warning." + + getLocation(Sec, Sym, Offset)); + } + + // Relax relocations. // - // On the other hand, if we know that a PLT entry will be resolved within - // the same ELF module, we can skip PLT access and directly jump to the - // destination function. For example, if we are linking a main exectuable, - // all dynamic symbols that can be resolved within the executable will - // actually be resolved that way at runtime, because the main exectuable - // is always at the beginning of a search list. We can leverage that fact. - if (Sym.isGnuIFunc() && !Config->ZIfuncnoplt) { - if (!Config->ZText && Config->WarnIfuncTextrel) { - warn("using ifunc symbols when text relocations are allowed may produce " - "a binary that will segfault, if the object file is linked with " - "old version of glibc (glibc 2.28 and earlier). If this applies to " - "you, consider recompiling the object files without -fPIC and " - "without -Wl,-z,notext option. Use -no-warn-ifunc-textrel to " - "turn off this warning." + - getLocation(Sec, Sym, Offset)); - } - Expr = toPlt(Expr); - } else if (!Sym.IsPreemptible && Expr == R_GOT_PC && !isAbsoluteValue(Sym)) { - Expr = Target->adjustRelaxExpr(Type, RelocatedAddr, Expr); - } else if (!Sym.IsPreemptible) { - Expr = fromPlt(Expr); + // If we know that a PLT entry will be resolved within the same ELF module, we + // can skip PLT access and directly jump to the destination function. For + // example, if we are linking a main exectuable, all dynamic symbols that can + // be resolved within the executable will actually be resolved that way at + // runtime, because the main exectuable is always at the beginning of a search + // list. We can leverage that fact. + if (!Sym.IsPreemptible && (!Sym.isGnuIFunc() || Config->ZIfuncnoplt)) { + if (Expr == R_GOT_PC && !isAbsoluteValue(Sym)) + Expr = Target->adjustRelaxExpr(Type, RelocatedAddr, Expr); + else + Expr = fromPlt(Expr); } // This relocation does not require got entry, but it is relative to got and @@ -1054,28 +1045,136 @@ return; } - // If a relocation needs PLT, we create PLT and GOTPLT slots for the symbol. - if (needsPlt(Expr) && !Sym.isInPlt()) { - if (Sym.isGnuIFunc() && !Sym.IsPreemptible) - addPltEntry(In.Iplt, In.IgotPlt, In.RelaIplt, Target->IRelativeRel, - Sym); - else + // Non-preemptible ifuncs require special handling. First, handle the usual + // case where the symbol isn't one of these. + if (!Sym.isGnuIFunc() || Sym.IsPreemptible) { + // If a relocation needs PLT, we create PLT and GOTPLT slots for the symbol. + if (needsPlt(Expr) && !Sym.isInPlt()) addPltEntry(In.Plt, In.GotPlt, In.RelaPlt, Target->PltRel, Sym); - } - // Create a GOT slot if a relocation needs GOT. - if (needsGot(Expr)) { - if (Config->EMachine == EM_MIPS) { - // MIPS ABI has special rules to process GOT entries and doesn't - // require relocation entries for them. A special case is TLS - // relocations. In that case dynamic loader applies dynamic - // relocations to initialize TLS GOT entries. - // See "Global Offset Table" in Chapter 5 in the following document - // for detailed description: - // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf - In.MipsGot->addEntry(*Sec.File, Sym, Addend, Expr); - } else if (!Sym.isInGot()) { - addGotEntry(Sym); + // Create a GOT slot if a relocation needs GOT. + if (needsGot(Expr)) { + if (Config->EMachine == EM_MIPS) { + // MIPS ABI has special rules to process GOT entries and doesn't + // require relocation entries for them. A special case is TLS + // relocations. In that case dynamic loader applies dynamic + // relocations to initialize TLS GOT entries. + // See "Global Offset Table" in Chapter 5 in the following document + // for detailed description: + // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf + In.MipsGot->addEntry(*Sec.File, Sym, Addend, Expr); + } else if (!Sym.isInGot()) { + addGotEntry(Sym); + } + } + } else { + // Handle a reference to a non-preemptible ifunc. These are special in a + // few ways: + // + // - Unlike most non-preemptible symbols, non-preemptible ifuncs do not have + // a fixed value. But assuming that all references to the ifunc are + // GOT-generating or PLT-generating, the handling of an ifunc is + // relatively straightforward. We create a PLT entry in Iplt, which is + // usually at the end of .plt, which makes an indirect call using a + // matching GOT entry in IgotPlt, which is usually at the end of .got.plt. + // The GOT entry is relocated using an IRELATIVE relocation in RelaIplt, + // which is usually at the end of .rela.plt. Unlike most relocations in + // .rela.plt, which may be evaluated lazily without -z now, dynamic + // loaders evaluate IRELATIVE relocs eagerly, which means that for + // IRELATIVE relocs only, GOT-generating relocations can point directly to + // .got.plt without requiring a separate GOT entry. + // + // - Despite the fact that an ifunc does not have a fixed value, compilers + // that are not passed -fPIC will assume that they do, and will emit + // direct (non-GOT-generating, non-PLT-generating) relocations to the + // symbol. This means that if a direct relocation to the symbol is + // seen, the linker must set a value for the symbol, and this value must + // be consistent no matter what type of reference is made to the symbol. + // This can be done by creating a PLT entry for the symbol in the way + // described above and making it canonical, that is, making all references + // point to the PLT entry instead of the resolver. In lld we also store + // the address of the PLT entry in the dynamic symbol table, which means + // that the symbol will also have the same value in other modules. + // Because the value loaded from the GOT needs to be consistent with + // the value computed using a direct relocation, a non-preemptible ifunc + // may end up with two GOT entries, one in .got.plt that points to the + // address returned by the resolver and is used only by the PLT entry, + // and another in .got that points to the PLT entry and is used by + // GOT-generating relocations. + // + // - The fact that these symbols do not have a fixed value makes them an + // exception to the general rule that a statically linked executable does + // not require any form of dynamic relocation. To handle these relocations + // correctly, the IRELATIVE relocations are stored in an array which a + // statically linked executable's startup code must enumerate using the + // linker-defined symbols __rela?_iplt_{start,end}. + // + // - An absolute relocation to a non-preemptible ifunc (such as a global + // variable containing a pointer to the ifunc) needs to be relocated in + // the exact same way as a GOT entry, so we can avoid needing to make the + // PLT entry canonical by translating such relocations into IRELATIVE + // relocations in the RelaIplt. + if (!Sym.isInPlt()) { + // Create PLT and GOTPLT slots for the symbol. + Sym.IsInIplt = true; + + // Create a copy of the symbol to use as the target of the IRELATIVE + // relocation in the IgotPlt. This is in case we make the PLT canonical + // later, which would overwrite the original symbol. + // + // FIXME: Creating a copy of the symbol here is a bit of a hack. All + // that's really needed to create the IRELATIVE is the section and value, + // so ideally we should just need to copy those. + auto *DirectSym = make(cast(Sym)); + addPltEntry(In.Iplt, In.IgotPlt, In.RelaIplt, Target->IRelativeRel, + *DirectSym); + Sym.PltIndex = DirectSym->PltIndex; + } + if (Expr == R_ABS && Addend == 0 && (Sec.Flags & SHF_WRITE)) { + // We might be able to represent this as an IRELATIVE. But we don't know + // yet whether some later relocation will make the symbol point to a + // canonical PLT, which would make this either a dynamic RELATIVE (PIC) or + // static (non-PIC) relocation. So we keep a record of the information + // required to process the relocation, and after scanRelocs() has been + // called on all relocations, the relocation is resolved by + // addIRelativeRelocs(). + IRelativeRelocs.push_back({Type, &Sec, Offset, &Sym}); + return; + } + if (needsGot(Expr)) { + // Redirect GOT accesses to point to the Igot. + // + // This field is also used to keep track of whether we ever needed a GOT + // entry. If we did and we make the PLT canonical later, we'll need to + // create a GOT entry pointing to the PLT entry for Sym. + Sym.GotInIgot = true; + } else if (!needsPlt(Expr)) { + // Make the ifunc's PLT entry canonical by changing the value of its + // symbol to redirect all references to point to it. + unsigned EntryOffset = Sym.PltIndex * Target->PltEntrySize; + if (Config->ZRetpolineplt) + EntryOffset += Target->PltHeaderSize; + + auto &D = cast(Sym); + D.Section = In.Iplt; + D.Value = EntryOffset; + D.Size = 0; + // It's important to set the symbol type here so that dynamic loaders + // don't try to call the PLT as if it were an ifunc resolver. + D.Type = STT_FUNC; + + if (Sym.GotInIgot) { + // We previously encountered a GOT generating reference that we + // redirected to the Igot. Now that the PLT entry is canonical we must + // clear the redirection to the Igot and add a GOT entry. As we've + // changed the symbol type to STT_FUNC future GOT generating references + // will naturally use this GOT entry. + // + // We don't need to worry about creating a MIPS GOT here because ifuncs + // aren't a thing on MIPS. + Sym.GotInIgot = false; + addGotEntry(Sym); + } } } @@ -1105,6 +1204,21 @@ scanRelocs(S, S.rels()); } +// Figure out which representation to use for any absolute relocs to +// non-preemptible ifuncs that we visited during scanRelocs(). +void elf::addIRelativeRelocs() { + for (IRelativeReloc &R : IRelativeRelocs) { + if (R.Sym->Type == STT_GNU_IFUNC) + In.RelaIplt->addReloc( + {Target->IRelativeRel, R.Sec, R.Offset, true, R.Sym, 0}); + else if (Config->Pic) + addRelativeReloc(R.Sec, R.Offset, R.Sym, 0, R_ABS, R.Type); + else + R.Sec->Relocations.push_back({R_ABS, R.Type, R.Offset, 0, R.Sym}); + } + IRelativeRelocs.clear(); +} + static bool mergeCmp(const InputSection *A, const InputSection *B) { // std::merge requires a strict weak ordering. if (A->OutSecOff < B->OutSecOff) Index: contrib/llvm/tools/lld/ELF/Symbols.h =================================================================== --- contrib/llvm/tools/lld/ELF/Symbols.h +++ contrib/llvm/tools/lld/ELF/Symbols.h @@ -182,7 +182,7 @@ uint8_t StOther, uint8_t Type) : File(File), NameData(Name.Data), NameSize(Name.Size), Binding(Binding), Type(Type), StOther(StOther), SymbolKind(K), NeedsPltAddr(false), - IsInIplt(false), IsInIgot(false), IsPreemptible(false), + IsInIplt(false), GotInIgot(false), IsPreemptible(false), Used(!Config->GcSections), NeedsTocRestore(false), ScriptDefined(false) {} @@ -191,11 +191,13 @@ // For SharedSymbol only. unsigned NeedsPltAddr : 1; - // True if this symbol is in the Iplt sub-section of the Plt. + // True if this symbol is in the Iplt sub-section of the Plt and the Igot + // sub-section of the .got.plt or .got. unsigned IsInIplt : 1; - // True if this symbol is in the Igot sub-section of the .got.plt or .got. - unsigned IsInIgot : 1; + // True if this symbol needs a GOT entry and its GOT entry is actually in + // Igot. This will be true only for certain non-preemptible ifuncs. + unsigned GotInIgot : 1; // True if this symbol is preemptible at load time. unsigned IsPreemptible : 1; Index: contrib/llvm/tools/lld/ELF/Symbols.cpp =================================================================== --- contrib/llvm/tools/lld/ELF/Symbols.cpp +++ contrib/llvm/tools/lld/ELF/Symbols.cpp @@ -121,20 +121,24 @@ return OutVA + Addend; } -uint64_t Symbol::getGotVA() const { return In.Got->getVA() + getGotOffset(); } +uint64_t Symbol::getGotVA() const { + if (GotInIgot) + return In.IgotPlt->getVA() + getGotPltOffset(); + return In.Got->getVA() + getGotOffset(); +} uint64_t Symbol::getGotOffset() const { return GotIndex * Target->GotEntrySize; } uint64_t Symbol::getGotPltVA() const { - if (this->IsInIgot) + if (IsInIplt) return In.IgotPlt->getVA() + getGotPltOffset(); return In.GotPlt->getVA() + getGotPltOffset(); } uint64_t Symbol::getGotPltOffset() const { - if (IsInIgot) + if (IsInIplt) return PltIndex * Target->GotPltEntrySize; return (PltIndex + Target->GotPltHeaderEntriesNum) * Target->GotPltEntrySize; } Index: contrib/llvm/tools/lld/ELF/SyntheticSections.cpp =================================================================== --- contrib/llvm/tools/lld/ELF/SyntheticSections.cpp +++ contrib/llvm/tools/lld/ELF/SyntheticSections.cpp @@ -1133,7 +1133,6 @@ Target->GotPltEntrySize, getIgotPltName()) {} void IgotPltSection::addEntry(Symbol &Sym) { - Sym.IsInIgot = true; assert(Sym.PltIndex == Entries.size()); Entries.push_back(&Sym); } @@ -2340,10 +2339,8 @@ template void PltSection::addEntry(Symbol &Sym) { Sym.PltIndex = Entries.size(); RelocationBaseSection *PltRelocSection = In.RelaPlt; - if (IsIplt) { + if (IsIplt) PltRelocSection = In.RelaIplt; - Sym.IsInIplt = true; - } unsigned RelOff = static_cast *>(PltRelocSection)->getRelocOffset(); Entries.push_back(std::make_pair(&Sym, RelOff)); Index: contrib/llvm/tools/lld/ELF/Writer.cpp =================================================================== --- contrib/llvm/tools/lld/ELF/Writer.cpp +++ contrib/llvm/tools/lld/ELF/Writer.cpp @@ -1668,6 +1668,8 @@ if (!Config->Relocatable) forEachRelSec(scanRelocations); + addIRelativeRelocs(); + if (In.Plt && !In.Plt->empty()) In.Plt->addSymbols(); if (In.Iplt && !In.Iplt->empty())