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Index: sys/arm/arm/elf_machdep.c
===================================================================
--- sys/arm/arm/elf_machdep.c
+++ sys/arm/arm/elf_machdep.c
@@ -47,6 +47,7 @@
#include <machine/elf.h>
#include <machine/md_var.h>
+#include <machine/stack.h>
#ifdef VFP
#include <machine/vfp.h>
#endif
@@ -309,12 +310,21 @@
cpu_l2cache_wb_range((vm_offset_t)lf->address, (vm_size_t)lf->size);
cpu_icache_sync_range((vm_offset_t)lf->address, (vm_size_t)lf->size);
#endif
+
+ /*
+ * Inform the stack(9) code of the new module, so it can acquire its
+ * per-module unwind data.
+ */
+ unwind_module_loaded(lf);
+
return (0);
}
int
-elf_cpu_unload_file(linker_file_t lf __unused)
+elf_cpu_unload_file(linker_file_t lf)
{
+ /* Inform the stack(9) code that this module is gone. */
+ unwind_module_unloaded(lf);
return (0);
}
Index: sys/arm/arm/unwind.c
===================================================================
--- sys/arm/arm/unwind.c
+++ sys/arm/arm/unwind.c
@@ -32,8 +32,11 @@
__FBSDID("$FreeBSD$");
#include <sys/param.h>
-#include <sys/systm.h>
+#include <sys/kernel.h>
#include <sys/linker.h>
+#include <sys/malloc.h>
+#include <sys/queue.h>
+#include <sys/systm.h>
#include <machine/machdep.h>
#include <machine/stack.h>
@@ -94,79 +97,238 @@
uint32_t insn;
};
-/* Expand a 31-bit signed value to a 32-bit signed value */
-static __inline int32_t
-expand_prel31(uint32_t prel31)
+/*
+ * Local cache of unwind info for loaded modules.
+ *
+ * To unwind the stack through the code in a loaded module, we need to access
+ * the module's exidx unwind data. To locate that data, one must search the
+ * elf section headers for the SHT_ARM_EXIDX section. Those headers are
+ * available at the time the module is being loaded, but are discarded by time
+ * the load process has completed. Code in kern/link_elf.c locates the data we
+ * need and stores it into the linker_file structure before calling the arm
+ * machdep routine for handling loaded modules (in arm/elf_machdep.c). That
+ * function calls into this code to pass along the unwind info, which we save
+ * into one of these module_info structures.
+ *
+ * Because we have to help stack(9) gather stack info at any time, including in
+ * contexts where sleeping is not allowed, we cannot use linker_file_foreach()
+ * to walk the kernel's list of linker_file structs, because doing so requires
+ * acquiring an exclusive sx_lock. So instead, we keep a local list of these
+ * structures, one for each loaded module (and one for the kernel itself that we
+ * synthesize at init time). New entries are added to the end of this list as
+ * needed, but entries are never deleted from the list. Instead, they are
+ * cleared out in-place to mark them as unused. That means the code doing stack
+ * unwinding can always safely walk the list without locking, because the
+ * structure of the list never changes in a way that would cause the walker to
+ * follow a bad link.
+ *
+ * A cleared-out entry on the list has module start=UINTPTR_MAX and end=0, so
+ * start <= addr < end cannot be true for any value of addr being searched for.
+ * We also don't have to worry about races where we look up the unwind info just
+ * before a module is unloaded and try to access it concurrently with or just
+ * after the unloading happens in another thread, because that means the path of
+ * execution leads through a now-unloaded module, and that's already well into
+ * undefined-behavior territory.
+ *
+ * List entries marked as unused get reused when new modules are loaded. We
+ * don't worry about holding a few unused bytes of memory in the list after
+ * unloading a module. Even if you loaded 1000 modules, did something that used
+ * them, then unloaded them all, we'd be wasting about 20K. In real-world
+ * scenarios the waste will be maybe a couple hundred bytes at most.
+ */
+struct module_info {
+ uintptr_t module_start; /* Start of loaded module */
+ uintptr_t module_end; /* End of loaded module */
+ uintptr_t exidx_start; /* Start of unwind data */
+ uintptr_t exidx_end; /* End of unwind data */
+ STAILQ_ENTRY(module_info)
+ link; /* Link to next entry */
+};
+static STAILQ_HEAD(, module_info) module_list;
+
+/*
+ * Hide ugly casting in somewhat-less-ugly macros.
+ * CADDR - cast a pointer or number to caddr_t.
+ * UADDR - cast a pointer or number to uintptr_t.
+ */
+#define CADDR(addr) ((caddr_t)(void*)(uintptr_t)(addr))
+#define UADDR(addr) ((uintptr_t)(addr))
+
+/*
+ * Clear the info in an existing module_info entry on the list. The
+ * module_start/end addresses are set to values that cannot match any real
+ * memory address. The entry remains on the list, but will be ignored until it
+ * is populated with new data.
+ */
+static void
+clear_module_info(struct module_info *info)
{
+ info->module_start = UINTPTR_MAX;
+ info->module_end = 0;
+}
- return ((int32_t)(prel31 & 0x7fffffffu) << 1) / 2;
+/*
+ * Populate an existing module_info entry (which is already on the list) with
+ * the info for a new module.
+ */
+static void
+populate_module_info(struct module_info *info, linker_file_t lf)
+{
+
+ /*
+ * Careful! The module_start and module_end fields must not be set
+ * until all other data in the structure is valid.
+ */
+ info->exidx_start = UADDR(lf->exidx_addr);
+ info->exidx_end = UADDR(lf->exidx_addr) + lf->exidx_size;
+ info->module_start = UADDR(lf->address);
+ info->module_end = UADDR(lf->address) + lf->size;
}
-struct search_context {
- uint32_t addr;
- caddr_t exidx_start;
- caddr_t exidx_end;
-};
+/*
+ * Create a new empty module_info entry and add it to the tail of the list.
+ */
+static struct module_info *
+create_module_info(void)
+{
+ struct module_info *info;
-static int
-module_search(linker_file_t lf, void *context)
+ info = malloc(sizeof(*info), M_CACHE, M_WAITOK | M_ZERO);
+ clear_module_info(info);
+ STAILQ_INSERT_TAIL(&module_list, info, link);
+ return (info);
+}
+
+/*
+ * Search for a module_info entry on the list whose address range contains the
+ * given address. If the search address is zero (no module will be loaded at
+ * zero), then we're looking for an empty item to reuse, which is indicated by
+ * module_start being set to UINTPTR_MAX in the entry.
+ */
+static struct module_info *
+find_module_info(uintptr_t addr)
{
- struct search_context *sc = context;
- linker_symval_t symval;
- c_linker_sym_t sym;
+ struct module_info *info;
- if (lf->address <= (caddr_t)sc->addr &&
- (lf->address + lf->size) >= (caddr_t)sc->addr) {
- if ((LINKER_LOOKUP_SYMBOL(lf, "__exidx_start", &sym) == 0 ||
- LINKER_LOOKUP_SYMBOL(lf, "exidx_start", &sym) == 0) &&
- LINKER_SYMBOL_VALUES(lf, sym, &symval) == 0)
- sc->exidx_start = symval.value;
+ STAILQ_FOREACH(info, &module_list, link) {
+ if ((addr >= info->module_start && addr < info->module_end) ||
+ (addr == 0 && info->module_start == UINTPTR_MAX))
+ return (info);
+ }
+ return (NULL);
+}
- if ((LINKER_LOOKUP_SYMBOL(lf, "__exidx_end", &sym) == 0 ||
- LINKER_LOOKUP_SYMBOL(lf, "exidx_end", &sym) == 0) &&
- LINKER_SYMBOL_VALUES(lf, sym, &symval) == 0)
- sc->exidx_end = symval.value;
+/*
+ * Handle the loading of a new module by populating a module_info for it. This
+ * is called for both preloaded and dynamically loaded modules.
+ */
+void
+unwind_module_loaded(struct linker_file *lf)
+{
+ struct module_info *info;
- if (sc->exidx_start != NULL && sc->exidx_end != NULL)
- return (1);
- panic("Invalid module %s, no unwind tables\n", lf->filename);
+ /*
+ * A module that contains only data may have no unwind info; don't
+ * create any module info for it.
+ */
+ if (lf->exidx_size == 0)
+ return;
+
+ /*
+ * Find an unused entry in the existing list to reuse. If we don't find
+ * one, create a new one and link it into the list. This is the only
+ * place the module_list is modified. Adding a new entry to the list
+ * will not perturb any other threads currently walking the list. This
+ * function is invoked while kern_linker is still holding its lock
+ * to prevent its module list from being modified, so we don't have to
+ * worry about racing other threads doing an insert concurrently.
+ */
+ if ((info = find_module_info(0)) == NULL) {
+ info = create_module_info();
}
+ populate_module_info(info, lf);
+}
+
+/* Handle the unloading of a module. */
+void
+unwind_module_unloaded(struct linker_file *lf)
+{
+ struct module_info *info;
+
+ /*
+ * A module that contains only data may have no unwind info and there
+ * won't be a list entry for it.
+ */
+ if (lf->exidx_size == 0)
+ return;
+
+ /*
+ * When a module is unloaded, we clear the info out of its entry in the
+ * module list, making that entry available for later reuse.
+ */
+ if ((info = find_module_info(UADDR(lf->address))) == NULL) {
+ printf("arm unwind: module '%s' not on list at unload time\n",
+ lf->filename);
+ return;
+ }
+ clear_module_info(info);
+}
+
+/*
+ * Initialization must run fairly early, as soon as malloc(9) is available, and
+ * definitely before witness, which uses stack(9). We synthesize a module_info
+ * entry for the kernel, because unwind_module_loaded() doesn't get called for
+ * it. Also, it is unlike other modules in that the elf metadata for locating
+ * the unwind tables might be stripped, so instead we have to use the
+ * _exidx_start/end symbols created by ldscript.arm.
+ */
+static int
+module_info_init(void *arg __unused)
+{
+ struct linker_file thekernel;
+
+ STAILQ_INIT(&module_list);
+
+ thekernel.filename = "kernel";
+ thekernel.address = CADDR(&_start);
+ thekernel.size = UADDR(&_end) - UADDR(&_start);
+ thekernel.exidx_addr = CADDR(&_exidx_start);
+ thekernel.exidx_size = UADDR(&_exidx_end) - UADDR(&_exidx_start);
+ populate_module_info(create_module_info(), &thekernel);
+
return (0);
}
+SYSINIT(unwind_init, SI_SUB_KMEM, SI_ORDER_ANY, module_info_init, NULL);
+/* Expand a 31-bit signed value to a 32-bit signed value */
+static __inline int32_t
+expand_prel31(uint32_t prel31)
+{
+
+ return ((int32_t)(prel31 & 0x7fffffffu) << 1) / 2;
+}
+
/*
* Perform a binary search of the index table to find the function
* with the largest address that doesn't exceed addr.
*/
static struct unwind_idx *
-find_index(uint32_t addr, int search_modules)
+find_index(uint32_t addr)
{
- struct search_context sc;
- caddr_t idx_start, idx_end;
+ struct module_info *info;
unsigned int min, mid, max;
struct unwind_idx *start;
struct unwind_idx *item;
int32_t prel31_addr;
uint32_t func_addr;
- start = (struct unwind_idx *)&_exidx_start;
- idx_start = (caddr_t)&_exidx_start;
- idx_end = (caddr_t)&_exidx_end;
+ info = find_module_info(addr);
+ if (info == NULL)
+ return NULL;
- /* This may acquire a lock */
- if (search_modules) {
- bzero(&sc, sizeof(sc));
- sc.addr = addr;
- if (linker_file_foreach(module_search, &sc) != 0 &&
- sc.exidx_start != NULL && sc.exidx_end != NULL) {
- start = (struct unwind_idx *)sc.exidx_start;
- idx_start = sc.exidx_start;
- idx_end = sc.exidx_end;
- }
- }
-
min = 0;
- max = (idx_end - idx_start) / sizeof(struct unwind_idx);
+ max = (info->exidx_end - info->exidx_start) / sizeof(struct unwind_idx);
+ start = (struct unwind_idx *)CADDR(info->exidx_start);
while (min != max) {
mid = min + (max - min + 1) / 2;
@@ -377,11 +539,17 @@
return 0;
}
+/*
+ * Unwind a single stack frame.
+ * Return 0 on success or 1 if the stack cannot be unwound any further.
+ *
+ * XXX The can_lock argument is no longer germane; a sweep of callers should be
+ * made to remove it after this new code has proven itself for a while.
+ */
int
-unwind_stack_one(struct unwind_state *state, int can_lock)
+unwind_stack_one(struct unwind_state *state, int can_lock __unused)
{
struct unwind_idx *index;
- int finished;
/* Reset the mask of updated registers */
state->update_mask = 0;
@@ -390,26 +558,20 @@
state->start_pc = state->registers[PC];
/* Find the item to run */
- index = find_index(state->start_pc, can_lock);
+ index = find_index(state->start_pc);
+ if (index == NULL || index->insn == EXIDX_CANTUNWIND)
+ return 1;
- finished = 0;
- if (index->insn != EXIDX_CANTUNWIND) {
- if (index->insn & (1U << 31)) {
- /* The data is within the instruction */
- state->insn = &index->insn;
- } else {
- /* A prel31 offset to the unwind table */
- state->insn = (uint32_t *)
- ((uintptr_t)&index->insn +
- expand_prel31(index->insn));
- }
- /* Run the unwind function */
- finished = unwind_tab(state);
+ if (index->insn & (1U << 31)) {
+ /* The data is within the instruction */
+ state->insn = &index->insn;
+ } else {
+ /* A prel31 offset to the unwind table */
+ state->insn = (uint32_t *)
+ ((uintptr_t)&index->insn +
+ expand_prel31(index->insn));
}
- /* This is the top of the stack, finish */
- if (index->insn == EXIDX_CANTUNWIND)
- finished = 1;
-
- return (finished);
+ /* Run the unwind function, return its finished/not-finished status. */
+ return (unwind_tab(state));
}
Index: sys/arm/include/stack.h
===================================================================
--- sys/arm/include/stack.h
+++ sys/arm/include/stack.h
@@ -55,6 +55,14 @@
#define LR 14
#define PC 15
+#ifdef _KERNEL
+
int unwind_stack_one(struct unwind_state *, int);
+
+struct linker_file;
+void unwind_module_loaded(struct linker_file *);
+void unwind_module_unloaded(struct linker_file *);
+
+#endif
#endif /* !_MACHINE_STACK_H_ */
Index: sys/kern/kern_linker.c
===================================================================
--- sys/kern/kern_linker.c
+++ sys/kern/kern_linker.c
@@ -624,6 +624,10 @@
lf->ndeps = 0;
lf->deps = NULL;
lf->loadcnt = ++loadcnt;
+#ifdef __arm__
+ lf->exidx_addr = 0;
+ lf->exidx_size = 0;
+#endif
STAILQ_INIT(&lf->common);
TAILQ_INIT(&lf->modules);
TAILQ_INSERT_TAIL(&linker_files, lf, link);
Index: sys/kern/link_elf.c
===================================================================
--- sys/kern/link_elf.c
+++ sys/kern/link_elf.c
@@ -773,6 +773,50 @@
#endif
}
+#ifdef __arm__
+/*
+ * Locate the ARM exception/unwind table info for DDB and stack(9) use by
+ * searching for the section header that describes it. There may be no unwind
+ * info, for example in a module containing only data.
+ */
+static void
+link_elf_locate_exidx(linker_file_t lf, Elf_Shdr *shdr, int nhdr)
+{
+ int i;
+
+ for (i = 0; i < nhdr; i++) {
+ if (shdr[i].sh_type == SHT_ARM_EXIDX) {
+ lf->exidx_addr = shdr[i].sh_addr + lf->address;
+ lf->exidx_size = shdr[i].sh_size;
+ break;
+ }
+ }
+}
+
+/*
+ * Locate the section headers metadata in a preloaded module, then use it to
+ * locate the exception/unwind table in the module. The size of the metadata
+ * block is stored in a uint32 word immediately before the data itself, and a
+ * comment in preload_search_info() says it is safe to rely on that.
+ */
+static void
+link_elf_locate_exidx_preload(struct linker_file *lf, caddr_t modptr)
+{
+ uint32_t *modinfo;
+ Elf_Shdr *shdr;
+ uint32_t nhdr;
+
+ modinfo = (uint32_t *)preload_search_info(modptr,
+ MODINFO_METADATA | MODINFOMD_SHDR);
+ if (modinfo != NULL) {
+ shdr = (Elf_Shdr *)modinfo;
+ nhdr = modinfo[-1] / sizeof(Elf_Shdr);
+ link_elf_locate_exidx(lf, shdr, nhdr);
+ }
+}
+
+#endif /* __arm__ */
+
static int
link_elf_link_preload(linker_class_t cls, const char *filename,
linker_file_t *result)
@@ -828,6 +872,10 @@
lf->ctors_size = *ctors_sizep;
}
+#ifdef __arm__
+ link_elf_locate_exidx_preload(lf, modptr);
+#endif
+
error = parse_dynamic(ef);
if (error == 0)
error = parse_dpcpu(ef);
@@ -1225,6 +1273,11 @@
ef->ddbstrtab = ef->strbase;
nosyms:
+
+#ifdef __arm__
+ link_elf_locate_exidx(lf, shdr, hdr->e_shnum);
+#endif
+
error = link_elf_link_common_finish(lf);
if (error != 0)
goto out;

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