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// Copyright 2018 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// This library provides Symbolize() function that symbolizes program
// counters to their corresponding symbol names on linux platforms.
// This library has a minimal implementation of an ELF symbol table
// reader (i.e. it doesn't depend on libelf, etc.).
//
// The algorithm used in Symbolize() is as follows.
//
// 1. Go through a list of maps in /proc/self/maps and find the map
// containing the program counter.
//
// 2. Open the mapped file and find a regular symbol table inside.
// Iterate over symbols in the symbol table and look for the symbol
// containing the program counter. If such a symbol is found,
// obtain the symbol name, and demangle the symbol if possible.
// If the symbol isn't found in the regular symbol table (binary is
// stripped), try the same thing with a dynamic symbol table.
//
// Note that Symbolize() is originally implemented to be used in
// signal handlers, hence it doesn't use malloc() and other unsafe
// operations. It should be both thread-safe and async-signal-safe.
//
// Implementation note:
//
// We don't use heaps but only use stacks. We want to reduce the
// stack consumption so that the symbolizer can run on small stacks.
//
// Here are some numbers collected with GCC 4.1.0 on x86:
// - sizeof(Elf32_Sym) = 16
// - sizeof(Elf32_Shdr) = 40
// - sizeof(Elf64_Sym) = 24
// - sizeof(Elf64_Shdr) = 64
//
// This implementation is intended to be async-signal-safe but uses some
// functions which are not guaranteed to be so, such as memchr() and
// memmove(). We assume they are async-signal-safe.
#include <dlfcn.h>
#include <elf.h>
#include <fcntl.h>
#include <link.h> // For ElfW() macro.
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <algorithm>
#include <array>
#include <atomic>
#include <cerrno>
#include <cinttypes>
#include <climits>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include "absl/base/casts.h"
#include "absl/base/dynamic_annotations.h"
#include "absl/base/internal/low_level_alloc.h"
#include "absl/base/internal/raw_logging.h"
#include "absl/base/internal/spinlock.h"
#include "absl/base/port.h"
#include "absl/debugging/internal/demangle.h"
#include "absl/debugging/internal/vdso_support.h"
#include "absl/strings/string_view.h"
#if defined(__FreeBSD__) && !defined(ElfW)
#define ElfW(x) __ElfN(x)
#endif
namespace absl {
ABSL_NAMESPACE_BEGIN
// Value of argv[0]. Used by MaybeInitializeObjFile().
static char *argv0_value = nullptr;
void InitializeSymbolizer(const char *argv0) {
#ifdef ABSL_HAVE_VDSO_SUPPORT
// We need to make sure VDSOSupport::Init() is called before any setuid or
// chroot calls, so InitializeSymbolizer() should be called very early in the
// life of a program.
absl::debugging_internal::VDSOSupport::Init();
#endif
if (argv0_value != nullptr) {
free(argv0_value);
argv0_value = nullptr;
}
if (argv0 != nullptr && argv0[0] != '\0') {
argv0_value = strdup(argv0);
}
}
namespace debugging_internal {
namespace {
// Re-runs fn until it doesn't cause EINTR.
#define NO_INTR(fn) \
do { \
} while ((fn) < 0 && errno == EINTR)
// On Linux, ELF_ST_* are defined in <linux/elf.h>. To make this portable
// we define our own ELF_ST_BIND and ELF_ST_TYPE if not available.
#ifndef ELF_ST_BIND
#define ELF_ST_BIND(info) (((unsigned char)(info)) >> 4)
#endif
#ifndef ELF_ST_TYPE
#define ELF_ST_TYPE(info) (((unsigned char)(info)) & 0xF)
#endif
// Some platforms use a special .opd section to store function pointers.
const char kOpdSectionName[] = ".opd";
#if (defined(__powerpc__) && !(_CALL_ELF > 1)) || defined(__ia64)
// Use opd section for function descriptors on these platforms, the function
// address is the first word of the descriptor.
enum { kPlatformUsesOPDSections = 1 };
#else // not PPC or IA64
enum { kPlatformUsesOPDSections = 0 };
#endif
// This works for PowerPC & IA64 only. A function descriptor consist of two
// pointers and the first one is the function's entry.
const size_t kFunctionDescriptorSize = sizeof(void *) * 2;
const int kMaxDecorators = 10; // Seems like a reasonable upper limit.
struct InstalledSymbolDecorator {
SymbolDecorator fn;
void *arg;
int ticket;
};
int g_num_decorators;
InstalledSymbolDecorator g_decorators[kMaxDecorators];
struct FileMappingHint {
const void *start;
const void *end;
uint64_t offset;
const char *filename;
};
// Protects g_decorators.
// We are using SpinLock and not a Mutex here, because we may be called
// from inside Mutex::Lock itself, and it prohibits recursive calls.
// This happens in e.g. base/stacktrace_syscall_unittest.
// Moreover, we are using only TryLock(), if the decorator list
// is being modified (is busy), we skip all decorators, and possibly
// loose some info. Sorry, that's the best we could do.
ABSL_CONST_INIT absl::base_internal::SpinLock g_decorators_mu(
absl::kConstInit, absl::base_internal::SCHEDULE_KERNEL_ONLY);
const int kMaxFileMappingHints = 8;
int g_num_file_mapping_hints;
FileMappingHint g_file_mapping_hints[kMaxFileMappingHints];
// Protects g_file_mapping_hints.
ABSL_CONST_INIT absl::base_internal::SpinLock g_file_mapping_mu(
absl::kConstInit, absl::base_internal::SCHEDULE_KERNEL_ONLY);
// Async-signal-safe function to zero a buffer.
// memset() is not guaranteed to be async-signal-safe.
static void SafeMemZero(void* p, size_t size) {
unsigned char *c = static_cast<unsigned char *>(p);
while (size--) {
*c++ = 0;
}
}
struct ObjFile {
ObjFile()
: filename(nullptr),
start_addr(nullptr),
end_addr(nullptr),
offset(0),
fd(-1),
elf_type(-1) {
SafeMemZero(&elf_header, sizeof(elf_header));
SafeMemZero(&phdr[0], sizeof(phdr));
}
char *filename;
const void *start_addr;
const void *end_addr;
uint64_t offset;
// The following fields are initialized on the first access to the
// object file.
int fd;
int elf_type;
ElfW(Ehdr) elf_header;
// PT_LOAD program header describing executable code.
// Normally we expect just one, but SWIFT binaries have two.
// CUDA binaries have 3 (see cr/473913254 description).
std::array<ElfW(Phdr), 4> phdr;
};
// Build 4-way associative cache for symbols. Within each cache line, symbols
// are replaced in LRU order.
enum {
ASSOCIATIVITY = 4,
};
struct SymbolCacheLine {
const void *pc[ASSOCIATIVITY];
char *name[ASSOCIATIVITY];
// age[i] is incremented when a line is accessed. it's reset to zero if the
// i'th entry is read.
uint32_t age[ASSOCIATIVITY];
};
// ---------------------------------------------------------------
// An async-signal-safe arena for LowLevelAlloc
static std::atomic<base_internal::LowLevelAlloc::Arena *> g_sig_safe_arena;
static base_internal::LowLevelAlloc::Arena *SigSafeArena() {
return g_sig_safe_arena.load(std::memory_order_acquire);
}
static void InitSigSafeArena() {
if (SigSafeArena() == nullptr) {
base_internal::LowLevelAlloc::Arena *new_arena =
base_internal::LowLevelAlloc::NewArena(
base_internal::LowLevelAlloc::kAsyncSignalSafe);
base_internal::LowLevelAlloc::Arena *old_value = nullptr;
if (!g_sig_safe_arena.compare_exchange_strong(old_value, new_arena,
std::memory_order_release,
std::memory_order_relaxed)) {
// We lost a race to allocate an arena; deallocate.
base_internal::LowLevelAlloc::DeleteArena(new_arena);
}
}
}
// ---------------------------------------------------------------
// An AddrMap is a vector of ObjFile, using SigSafeArena() for allocation.
class AddrMap {
public:
AddrMap() : size_(0), allocated_(0), obj_(nullptr) {}
~AddrMap() { base_internal::LowLevelAlloc::Free(obj_); }
size_t Size() const { return size_; }
ObjFile *At(size_t i) { return &obj_[i]; }
ObjFile *Add();
void Clear();
private:
size_t size_; // count of valid elements (<= allocated_)
size_t allocated_; // count of allocated elements
ObjFile *obj_; // array of allocated_ elements
AddrMap(const AddrMap &) = delete;
AddrMap &operator=(const AddrMap &) = delete;
};
void AddrMap::Clear() {
for (size_t i = 0; i != size_; i++) {
At(i)->~ObjFile();
}
size_ = 0;
}
ObjFile *AddrMap::Add() {
if (size_ == allocated_) {
size_t new_allocated = allocated_ * 2 + 50;
ObjFile *new_obj_ =
static_cast<ObjFile *>(base_internal::LowLevelAlloc::AllocWithArena(
new_allocated * sizeof(*new_obj_), SigSafeArena()));
if (obj_) {
memcpy(new_obj_, obj_, allocated_ * sizeof(*new_obj_));
base_internal::LowLevelAlloc::Free(obj_);
}
obj_ = new_obj_;
allocated_ = new_allocated;
}
return new (&obj_[size_++]) ObjFile;
}
// ---------------------------------------------------------------
enum FindSymbolResult { SYMBOL_NOT_FOUND = 1, SYMBOL_TRUNCATED, SYMBOL_FOUND };
class Symbolizer {
public:
Symbolizer();
~Symbolizer();
const char *GetSymbol(const void *const pc);
private:
char *CopyString(const char *s) {
size_t len = strlen(s);
char *dst = static_cast<char *>(
base_internal::LowLevelAlloc::AllocWithArena(len + 1, SigSafeArena()));
ABSL_RAW_CHECK(dst != nullptr, "out of memory");
memcpy(dst, s, len + 1);
return dst;
}
ObjFile *FindObjFile(const void *const start,
size_t size) ABSL_ATTRIBUTE_NOINLINE;
static bool RegisterObjFile(const char *filename,
const void *const start_addr,
const void *const end_addr, uint64_t offset,
void *arg);
SymbolCacheLine *GetCacheLine(const void *const pc);
const char *FindSymbolInCache(const void *const pc);
const char *InsertSymbolInCache(const void *const pc, const char *name);
void AgeSymbols(SymbolCacheLine *line);
void ClearAddrMap();
FindSymbolResult GetSymbolFromObjectFile(const ObjFile &obj,
const void *const pc,
const ptrdiff_t relocation,
char *out, size_t out_size,
char *tmp_buf, size_t tmp_buf_size);
const char *GetUncachedSymbol(const void *pc);
enum {
SYMBOL_BUF_SIZE = 3072,
TMP_BUF_SIZE = 1024,
SYMBOL_CACHE_LINES = 128,
};
AddrMap addr_map_;
bool ok_;
bool addr_map_read_;
char symbol_buf_[SYMBOL_BUF_SIZE];
// tmp_buf_ will be used to store arrays of ElfW(Shdr) and ElfW(Sym)
// so we ensure that tmp_buf_ is properly aligned to store either.
alignas(16) char tmp_buf_[TMP_BUF_SIZE];
static_assert(alignof(ElfW(Shdr)) <= 16,
"alignment of tmp buf too small for Shdr");
static_assert(alignof(ElfW(Sym)) <= 16,
"alignment of tmp buf too small for Sym");
SymbolCacheLine symbol_cache_[SYMBOL_CACHE_LINES];
};
static std::atomic<Symbolizer *> g_cached_symbolizer;
} // namespace
static size_t SymbolizerSize() {
#if defined(__wasm__) || defined(__asmjs__)
auto pagesize = static_cast<size_t>(getpagesize());
#else
auto pagesize = static_cast<size_t>(sysconf(_SC_PAGESIZE));
#endif
return ((sizeof(Symbolizer) - 1) / pagesize + 1) * pagesize;
}
// Return (and set null) g_cached_symbolized_state if it is not null.
// Otherwise return a new symbolizer.
static Symbolizer *AllocateSymbolizer() {
InitSigSafeArena();
Symbolizer *symbolizer =
g_cached_symbolizer.exchange(nullptr, std::memory_order_acquire);
if (symbolizer != nullptr) {
return symbolizer;
}
return new (base_internal::LowLevelAlloc::AllocWithArena(
SymbolizerSize(), SigSafeArena())) Symbolizer();
}
// Set g_cached_symbolize_state to s if it is null, otherwise
// delete s.
static void FreeSymbolizer(Symbolizer *s) {
Symbolizer *old_cached_symbolizer = nullptr;
if (!g_cached_symbolizer.compare_exchange_strong(old_cached_symbolizer, s,
std::memory_order_release,
std::memory_order_relaxed)) {
s->~Symbolizer();
base_internal::LowLevelAlloc::Free(s);
}
}
Symbolizer::Symbolizer() : ok_(true), addr_map_read_(false) {
for (SymbolCacheLine &symbol_cache_line : symbol_cache_) {
for (size_t j = 0; j < ABSL_ARRAYSIZE(symbol_cache_line.name); ++j) {
symbol_cache_line.pc[j] = nullptr;
symbol_cache_line.name[j] = nullptr;
symbol_cache_line.age[j] = 0;
}
}
}
Symbolizer::~Symbolizer() {
for (SymbolCacheLine &symbol_cache_line : symbol_cache_) {
for (char *s : symbol_cache_line.name) {
base_internal::LowLevelAlloc::Free(s);
}
}
ClearAddrMap();
}
// We don't use assert() since it's not guaranteed to be
// async-signal-safe. Instead we define a minimal assertion
// macro. So far, we don't need pretty printing for __FILE__, etc.
#define SAFE_ASSERT(expr) ((expr) ? static_cast<void>(0) : abort())
// Read up to "count" bytes from file descriptor "fd" into the buffer
// starting at "buf" while handling short reads and EINTR. On
// success, return the number of bytes read. Otherwise, return -1.
static ssize_t ReadPersistent(int fd, void *buf, size_t count) {
SAFE_ASSERT(fd >= 0);
SAFE_ASSERT(count <= SSIZE_MAX);
char *buf0 = reinterpret_cast<char *>(buf);
size_t num_bytes = 0;
while (num_bytes < count) {
ssize_t len;
NO_INTR(len = read(fd, buf0 + num_bytes, count - num_bytes));
if (len < 0) { // There was an error other than EINTR.
ABSL_RAW_LOG(WARNING, "read failed: errno=%d", errno);
return -1;
}
if (len == 0) { // Reached EOF.
break;
}
num_bytes += static_cast<size_t>(len);
}
SAFE_ASSERT(num_bytes <= count);
return static_cast<ssize_t>(num_bytes);
}
// Read up to "count" bytes from "offset" in the file pointed by file
// descriptor "fd" into the buffer starting at "buf". On success,
// return the number of bytes read. Otherwise, return -1.
static ssize_t ReadFromOffset(const int fd, void *buf, const size_t count,
const off_t offset) {
off_t off = lseek(fd, offset, SEEK_SET);
if (off == (off_t)-1) {
ABSL_RAW_LOG(WARNING, "lseek(%d, %jd, SEEK_SET) failed: errno=%d", fd,
static_cast<intmax_t>(offset), errno);
return -1;
}
return ReadPersistent(fd, buf, count);
}
// Try reading exactly "count" bytes from "offset" bytes in a file
// pointed by "fd" into the buffer starting at "buf" while handling
// short reads and EINTR. On success, return true. Otherwise, return
// false.
static bool ReadFromOffsetExact(const int fd, void *buf, const size_t count,
const off_t offset) {
ssize_t len = ReadFromOffset(fd, buf, count, offset);
return len >= 0 && static_cast<size_t>(len) == count;
}
// Returns elf_header.e_type if the file pointed by fd is an ELF binary.
static int FileGetElfType(const int fd) {
ElfW(Ehdr) elf_header;
if (!ReadFromOffsetExact(fd, &elf_header, sizeof(elf_header), 0)) {
return -1;
}
if (memcmp(elf_header.e_ident, ELFMAG, SELFMAG) != 0) {
return -1;
}
return elf_header.e_type;
}
// Read the section headers in the given ELF binary, and if a section
// of the specified type is found, set the output to this section header
// and return true. Otherwise, return false.
// To keep stack consumption low, we would like this function to not get
// inlined.
static ABSL_ATTRIBUTE_NOINLINE bool GetSectionHeaderByType(
const int fd, ElfW(Half) sh_num, const off_t sh_offset, ElfW(Word) type,
ElfW(Shdr) * out, char *tmp_buf, size_t tmp_buf_size) {
ElfW(Shdr) *buf = reinterpret_cast<ElfW(Shdr) *>(tmp_buf);
const size_t buf_entries = tmp_buf_size / sizeof(buf[0]);
const size_t buf_bytes = buf_entries * sizeof(buf[0]);
for (size_t i = 0; static_cast<int>(i) < sh_num;) {
const size_t num_bytes_left =
(static_cast<size_t>(sh_num) - i) * sizeof(buf[0]);
const size_t num_bytes_to_read =
(buf_bytes > num_bytes_left) ? num_bytes_left : buf_bytes;
const off_t offset = sh_offset + static_cast<off_t>(i * sizeof(buf[0]));
const ssize_t len = ReadFromOffset(fd, buf, num_bytes_to_read, offset);
if (len < 0) {
ABSL_RAW_LOG(
WARNING,
"Reading %zu bytes from offset %ju returned %zd which is negative.",
num_bytes_to_read, static_cast<intmax_t>(offset), len);
return false;
}
if (static_cast<size_t>(len) % sizeof(buf[0]) != 0) {
ABSL_RAW_LOG(
WARNING,
"Reading %zu bytes from offset %jd returned %zd which is not a "
"multiple of %zu.",
num_bytes_to_read, static_cast<intmax_t>(offset), len,
sizeof(buf[0]));
return false;
}
const size_t num_headers_in_buf = static_cast<size_t>(len) / sizeof(buf[0]);
SAFE_ASSERT(num_headers_in_buf <= buf_entries);
for (size_t j = 0; j < num_headers_in_buf; ++j) {
if (buf[j].sh_type == type) {
*out = buf[j];
return true;
}
}
i += num_headers_in_buf;
}
return false;
}
// There is no particular reason to limit section name to 63 characters,
// but there has (as yet) been no need for anything longer either.
const int kMaxSectionNameLen = 64;
bool ForEachSection(int fd,
const std::function<bool(absl::string_view name,
const ElfW(Shdr) &)> &callback) {
ElfW(Ehdr) elf_header;
if (!ReadFromOffsetExact(fd, &elf_header, sizeof(elf_header), 0)) {
return false;
}
// Technically it can be larger, but in practice this never happens.
if (elf_header.e_shentsize != sizeof(ElfW(Shdr))) {
return false;
}
ElfW(Shdr) shstrtab;
off_t shstrtab_offset = static_cast<off_t>(elf_header.e_shoff) +
elf_header.e_shentsize * elf_header.e_shstrndx;
if (!ReadFromOffsetExact(fd, &shstrtab, sizeof(shstrtab), shstrtab_offset)) {
return false;
}
for (int i = 0; i < elf_header.e_shnum; ++i) {
ElfW(Shdr) out;
off_t section_header_offset =
static_cast<off_t>(elf_header.e_shoff) + elf_header.e_shentsize * i;
if (!ReadFromOffsetExact(fd, &out, sizeof(out), section_header_offset)) {
return false;
}
off_t name_offset = static_cast<off_t>(shstrtab.sh_offset) + out.sh_name;
char header_name[kMaxSectionNameLen];
ssize_t n_read =
ReadFromOffset(fd, &header_name, kMaxSectionNameLen, name_offset);
if (n_read < 0) {
return false;
} else if (n_read > kMaxSectionNameLen) {
// Long read?
return false;
}
absl::string_view name(header_name,
strnlen(header_name, static_cast<size_t>(n_read)));
if (!callback(name, out)) {
break;
}
}
return true;
}
// name_len should include terminating '\0'.
bool GetSectionHeaderByName(int fd, const char *name, size_t name_len,
ElfW(Shdr) * out) {
char header_name[kMaxSectionNameLen];
if (sizeof(header_name) < name_len) {
ABSL_RAW_LOG(WARNING,
"Section name '%s' is too long (%zu); "
"section will not be found (even if present).",
name, name_len);
// No point in even trying.
return false;
}
ElfW(Ehdr) elf_header;
if (!ReadFromOffsetExact(fd, &elf_header, sizeof(elf_header), 0)) {
return false;
}
// Technically it can be larger, but in practice this never happens.
if (elf_header.e_shentsize != sizeof(ElfW(Shdr))) {
return false;
}
ElfW(Shdr) shstrtab;
off_t shstrtab_offset = static_cast<off_t>(elf_header.e_shoff) +
elf_header.e_shentsize * elf_header.e_shstrndx;
if (!ReadFromOffsetExact(fd, &shstrtab, sizeof(shstrtab), shstrtab_offset)) {
return false;
}
for (int i = 0; i < elf_header.e_shnum; ++i) {
off_t section_header_offset =
static_cast<off_t>(elf_header.e_shoff) + elf_header.e_shentsize * i;
if (!ReadFromOffsetExact(fd, out, sizeof(*out), section_header_offset)) {
return false;
}
off_t name_offset = static_cast<off_t>(shstrtab.sh_offset) + out->sh_name;
ssize_t n_read = ReadFromOffset(fd, &header_name, name_len, name_offset);
if (n_read < 0) {
return false;
} else if (static_cast<size_t>(n_read) != name_len) {
// Short read -- name could be at end of file.
continue;
}
if (memcmp(header_name, name, name_len) == 0) {
return true;
}
}
return false;
}
// Compare symbols at in the same address.
// Return true if we should pick symbol1.
static bool ShouldPickFirstSymbol(const ElfW(Sym) & symbol1,
const ElfW(Sym) & symbol2) {
// If one of the symbols is weak and the other is not, pick the one
// this is not a weak symbol.
char bind1 = ELF_ST_BIND(symbol1.st_info);
char bind2 = ELF_ST_BIND(symbol1.st_info);
if (bind1 == STB_WEAK && bind2 != STB_WEAK) return false;
if (bind2 == STB_WEAK && bind1 != STB_WEAK) return true;
// If one of the symbols has zero size and the other is not, pick the
// one that has non-zero size.
if (symbol1.st_size != 0 && symbol2.st_size == 0) {
return true;
}
if (symbol1.st_size == 0 && symbol2.st_size != 0) {
return false;
}
// If one of the symbols has no type and the other is not, pick the
// one that has a type.
char type1 = ELF_ST_TYPE(symbol1.st_info);
char type2 = ELF_ST_TYPE(symbol1.st_info);
if (type1 != STT_NOTYPE && type2 == STT_NOTYPE) {
return true;
}
if (type1 == STT_NOTYPE && type2 != STT_NOTYPE) {
return false;
}
// Pick the first one, if we still cannot decide.
return true;
}
// Return true if an address is inside a section.
static bool InSection(const void *address, ptrdiff_t relocation,
const ElfW(Shdr) * section) {
const char *start = reinterpret_cast<const char *>(
section->sh_addr + static_cast<ElfW(Addr)>(relocation));
size_t size = static_cast<size_t>(section->sh_size);
return start <= address && address < (start + size);
}
static const char *ComputeOffset(const char *base, ptrdiff_t offset) {
// Note: cast to intptr_t to avoid undefined behavior when base evaluates to
// zero and offset is non-zero.
return reinterpret_cast<const char *>(reinterpret_cast<intptr_t>(base) +
offset);
}
// Read a symbol table and look for the symbol containing the
// pc. Iterate over symbols in a symbol table and look for the symbol
// containing "pc". If the symbol is found, and its name fits in
// out_size, the name is written into out and SYMBOL_FOUND is returned.
// If the name does not fit, truncated name is written into out,
// and SYMBOL_TRUNCATED is returned. Out is NUL-terminated.
// If the symbol is not found, SYMBOL_NOT_FOUND is returned;
// To keep stack consumption low, we would like this function to not get
// inlined.
static ABSL_ATTRIBUTE_NOINLINE FindSymbolResult FindSymbol(
const void *const pc, const int fd, char *out, size_t out_size,
ptrdiff_t relocation, const ElfW(Shdr) * strtab, const ElfW(Shdr) * symtab,
const ElfW(Shdr) * opd, char *tmp_buf, size_t tmp_buf_size) {
if (symtab == nullptr) {
return SYMBOL_NOT_FOUND;
}
// Read multiple symbols at once to save read() calls.
ElfW(Sym) *buf = reinterpret_cast<ElfW(Sym) *>(tmp_buf);
const size_t buf_entries = tmp_buf_size / sizeof(buf[0]);
const size_t num_symbols = symtab->sh_size / symtab->sh_entsize;
// On platforms using an .opd section (PowerPC & IA64), a function symbol
// has the address of a function descriptor, which contains the real
// starting address. However, we do not always want to use the real
// starting address because we sometimes want to symbolize a function
// pointer into the .opd section, e.g. FindSymbol(&foo,...).
const bool pc_in_opd = kPlatformUsesOPDSections && opd != nullptr &&
InSection(pc, relocation, opd);
const bool deref_function_descriptor_pointer =
kPlatformUsesOPDSections && opd != nullptr && !pc_in_opd;
ElfW(Sym) best_match;
SafeMemZero(&best_match, sizeof(best_match));
bool found_match = false;
for (size_t i = 0; i < num_symbols;) {
off_t offset =
static_cast<off_t>(symtab->sh_offset + i * symtab->sh_entsize);
const size_t num_remaining_symbols = num_symbols - i;
const size_t entries_in_chunk =
std::min(num_remaining_symbols, buf_entries);
const size_t bytes_in_chunk = entries_in_chunk * sizeof(buf[0]);
const ssize_t len = ReadFromOffset(fd, buf, bytes_in_chunk, offset);
SAFE_ASSERT(len >= 0);
SAFE_ASSERT(static_cast<size_t>(len) % sizeof(buf[0]) == 0);
const size_t num_symbols_in_buf = static_cast<size_t>(len) / sizeof(buf[0]);
SAFE_ASSERT(num_symbols_in_buf <= entries_in_chunk);
for (size_t j = 0; j < num_symbols_in_buf; ++j) {
const ElfW(Sym) &symbol = buf[j];
// For a DSO, a symbol address is relocated by the loading address.
// We keep the original address for opd redirection below.
const char *const original_start_address =
reinterpret_cast<const char *>(symbol.st_value);
const char *start_address =
ComputeOffset(original_start_address, relocation);
#ifdef __arm__
// ARM functions are always aligned to multiples of two bytes; the
// lowest-order bit in start_address is ignored by the CPU and indicates
// whether the function contains ARM (0) or Thumb (1) code. We don't care
// about what encoding is being used; we just want the real start address
// of the function.
start_address = reinterpret_cast<const char *>(
reinterpret_cast<uintptr_t>(start_address) & ~1u);
#endif
if (deref_function_descriptor_pointer &&
InSection(original_start_address, /*relocation=*/0, opd)) {
// The opd section is mapped into memory. Just dereference
// start_address to get the first double word, which points to the
// function entry.
start_address = *reinterpret_cast<const char *const *>(start_address);
}
// If pc is inside the .opd section, it points to a function descriptor.
const size_t size = pc_in_opd ? kFunctionDescriptorSize : symbol.st_size;
const void *const end_address =
ComputeOffset(start_address, static_cast<ptrdiff_t>(size));
if (symbol.st_value != 0 && // Skip null value symbols.
symbol.st_shndx != 0 && // Skip undefined symbols.
#ifdef STT_TLS
ELF_ST_TYPE(symbol.st_info) != STT_TLS && // Skip thread-local data.
#endif // STT_TLS
((start_address <= pc && pc < end_address) ||
(start_address == pc && pc == end_address))) {
if (!found_match || ShouldPickFirstSymbol(symbol, best_match)) {
found_match = true;
best_match = symbol;
}
}
}
i += num_symbols_in_buf;
}
if (found_match) {
const off_t off =
static_cast<off_t>(strtab->sh_offset) + best_match.st_name;
const ssize_t n_read = ReadFromOffset(fd, out, out_size, off);
if (n_read <= 0) {
// This should never happen.
ABSL_RAW_LOG(WARNING,
"Unable to read from fd %d at offset %lld: n_read = %zd", fd,
static_cast<long long>(off), n_read);
return SYMBOL_NOT_FOUND;
}
ABSL_RAW_CHECK(static_cast<size_t>(n_read) <= out_size,
"ReadFromOffset read too much data.");
// strtab->sh_offset points into .strtab-like section that contains
// NUL-terminated strings: '\0foo\0barbaz\0...".
//
// sh_offset+st_name points to the start of symbol name, but we don't know
// how long the symbol is, so we try to read as much as we have space for,
// and usually over-read (i.e. there is a NUL somewhere before n_read).
if (memchr(out, '\0', static_cast<size_t>(n_read)) == nullptr) {
// Either out_size was too small (n_read == out_size and no NUL), or
// we tried to read past the EOF (n_read < out_size) and .strtab is
// corrupt (missing terminating NUL; should never happen for valid ELF).
out[n_read - 1] = '\0';
return SYMBOL_TRUNCATED;
}
return SYMBOL_FOUND;
}
return SYMBOL_NOT_FOUND;
}
// Get the symbol name of "pc" from the file pointed by "fd". Process
// both regular and dynamic symbol tables if necessary.
// See FindSymbol() comment for description of return value.
FindSymbolResult Symbolizer::GetSymbolFromObjectFile(
const ObjFile &obj, const void *const pc, const ptrdiff_t relocation,
char *out, size_t out_size, char *tmp_buf, size_t tmp_buf_size) {
ElfW(Shdr) symtab;
ElfW(Shdr) strtab;
ElfW(Shdr) opd;
ElfW(Shdr) *opd_ptr = nullptr;
// On platforms using an .opd sections for function descriptor, read
// the section header. The .opd section is in data segment and should be
// loaded but we check that it is mapped just to be extra careful.
if (kPlatformUsesOPDSections) {
if (GetSectionHeaderByName(obj.fd, kOpdSectionName,
sizeof(kOpdSectionName) - 1, &opd) &&
FindObjFile(reinterpret_cast<const char *>(opd.sh_addr) + relocation,
opd.sh_size) != nullptr) {
opd_ptr = &opd;
} else {
return SYMBOL_NOT_FOUND;
}
}
// Consult a regular symbol table, then fall back to the dynamic symbol table.
for (const auto symbol_table_type : {SHT_SYMTAB, SHT_DYNSYM}) {
if (!GetSectionHeaderByType(obj.fd, obj.elf_header.e_shnum,
static_cast<off_t>(obj.elf_header.e_shoff),
static_cast<ElfW(Word)>(symbol_table_type),
&symtab, tmp_buf, tmp_buf_size)) {
continue;
}
if (!ReadFromOffsetExact(
obj.fd, &strtab, sizeof(strtab),
static_cast<off_t>(obj.elf_header.e_shoff +
symtab.sh_link * sizeof(symtab)))) {
continue;
}
const FindSymbolResult rc =
FindSymbol(pc, obj.fd, out, out_size, relocation, &strtab, &symtab,
opd_ptr, tmp_buf, tmp_buf_size);
if (rc != SYMBOL_NOT_FOUND) {
return rc;
}
}
return SYMBOL_NOT_FOUND;
}
namespace {
// Thin wrapper around a file descriptor so that the file descriptor
// gets closed for sure.
class FileDescriptor {
public:
explicit FileDescriptor(int fd) : fd_(fd) {}
FileDescriptor(const FileDescriptor &) = delete;
FileDescriptor &operator=(const FileDescriptor &) = delete;
~FileDescriptor() {
if (fd_ >= 0) {
close(fd_);
}
}
int get() const { return fd_; }
private:
const int fd_;
};
// Helper class for reading lines from file.
//
// Note: we don't use ProcMapsIterator since the object is big (it has
// a 5k array member) and uses async-unsafe functions such as sscanf()
// and snprintf().
class LineReader {
public:
explicit LineReader(int fd, char *buf, size_t buf_len)
: fd_(fd),
buf_len_(buf_len),
buf_(buf),
bol_(buf),
eol_(buf),
eod_(buf) {}
LineReader(const LineReader &) = delete;
LineReader &operator=(const LineReader &) = delete;
// Read '\n'-terminated line from file. On success, modify "bol"
// and "eol", then return true. Otherwise, return false.
//
// Note: if the last line doesn't end with '\n', the line will be
// dropped. It's an intentional behavior to make the code simple.
bool ReadLine(const char **bol, const char **eol) {
if (BufferIsEmpty()) { // First time.
const ssize_t num_bytes = ReadPersistent(fd_, buf_, buf_len_);
if (num_bytes <= 0) { // EOF or error.
return false;
}
eod_ = buf_ + num_bytes;
bol_ = buf_;
} else {
bol_ = eol_ + 1; // Advance to the next line in the buffer.
SAFE_ASSERT(bol_ <= eod_); // "bol_" can point to "eod_".
if (!HasCompleteLine()) {
const auto incomplete_line_length = static_cast<size_t>(eod_ - bol_);
// Move the trailing incomplete line to the beginning.
memmove(buf_, bol_, incomplete_line_length);
// Read text from file and append it.
char *const append_pos = buf_ + incomplete_line_length;
const size_t capacity_left = buf_len_ - incomplete_line_length;
const ssize_t num_bytes =
ReadPersistent(fd_, append_pos, capacity_left);
if (num_bytes <= 0) { // EOF or error.
return false;
}
eod_ = append_pos + num_bytes;
bol_ = buf_;
}
}
eol_ = FindLineFeed();
if (eol_ == nullptr) { // '\n' not found. Malformed line.
return false;
}
*eol_ = '\0'; // Replace '\n' with '\0'.
*bol = bol_;
*eol = eol_;
return true;
}
private:
char *FindLineFeed() const {
return reinterpret_cast<char *>(
memchr(bol_, '\n', static_cast<size_t>(eod_ - bol_)));
}
bool BufferIsEmpty() const { return buf_ == eod_; }
bool HasCompleteLine() const {
return !BufferIsEmpty() && FindLineFeed() != nullptr;
}
const int fd_;
const size_t buf_len_;
char *const buf_;
char *bol_;
char *eol_;
const char *eod_; // End of data in "buf_".
};
} // namespace
// Place the hex number read from "start" into "*hex". The pointer to
// the first non-hex character or "end" is returned.
static const char *GetHex(const char *start, const char *end,
uint64_t *const value) {
uint64_t hex = 0;
const char *p;
for (p = start; p < end; ++p) {
int ch = *p;
if ((ch >= '0' && ch <= '9') || (ch >= 'A' && ch <= 'F') ||
(ch >= 'a' && ch <= 'f')) {
hex = (hex << 4) |
static_cast<uint64_t>(ch < 'A' ? ch - '0' : (ch & 0xF) + 9);
} else { // Encountered the first non-hex character.
break;
}
}
SAFE_ASSERT(p <= end);
*value = hex;
return p;
}
static const char *GetHex(const char *start, const char *end,
const void **const addr) {
uint64_t hex = 0;
const char *p = GetHex(start, end, &hex);
*addr = reinterpret_cast<void *>(hex);
return p;
}
// Normally we are only interested in "r?x" maps.
// On the PowerPC, function pointers point to descriptors in the .opd
// section. The descriptors themselves are not executable code, so
// we need to relax the check below to "r??".
static bool ShouldUseMapping(const char *const flags) {
return flags[0] == 'r' && (kPlatformUsesOPDSections || flags[2] == 'x');
}
// Read /proc/self/maps and run "callback" for each mmapped file found. If
// "callback" returns false, stop scanning and return true. Else continue
// scanning /proc/self/maps. Return true if no parse error is found.
static ABSL_ATTRIBUTE_NOINLINE bool ReadAddrMap(
bool (*callback)(const char *filename, const void *const start_addr,
const void *const end_addr, uint64_t offset, void *arg),
void *arg, void *tmp_buf, size_t tmp_buf_size) {
// Use /proc/self/task/<pid>/maps instead of /proc/self/maps. The latter
// requires kernel to stop all threads, and is significantly slower when there
// are 1000s of threads.
char maps_path[80];
snprintf(maps_path, sizeof(maps_path), "/proc/self/task/%d/maps", getpid());
int maps_fd;
NO_INTR(maps_fd = open(maps_path, O_RDONLY));
FileDescriptor wrapped_maps_fd(maps_fd);
if (wrapped_maps_fd.get() < 0) {
ABSL_RAW_LOG(WARNING, "%s: errno=%d", maps_path, errno);
return false;
}
// Iterate over maps and look for the map containing the pc. Then
// look into the symbol tables inside.
LineReader reader(wrapped_maps_fd.get(), static_cast<char *>(tmp_buf),
tmp_buf_size);
while (true) {
const char *cursor;
const char *eol;
if (!reader.ReadLine(&cursor, &eol)) { // EOF or malformed line.
break;
}
const char *line = cursor;
const void *start_address;
// Start parsing line in /proc/self/maps. Here is an example:
//
// 08048000-0804c000 r-xp 00000000 08:01 2142121 /bin/cat
//
// We want start address (08048000), end address (0804c000), flags
// (r-xp) and file name (/bin/cat).
// Read start address.
cursor = GetHex(cursor, eol, &start_address);
if (cursor == eol || *cursor != '-') {
ABSL_RAW_LOG(WARNING, "Corrupt /proc/self/maps line: %s", line);
return false;
}
++cursor; // Skip '-'.
// Read end address.
const void *end_address;
cursor = GetHex(cursor, eol, &end_address);
if (cursor == eol || *cursor != ' ') {
ABSL_RAW_LOG(WARNING, "Corrupt /proc/self/maps line: %s", line);
return false;
}
++cursor; // Skip ' '.
// Read flags. Skip flags until we encounter a space or eol.
const char *const flags_start = cursor;
while (cursor < eol && *cursor != ' ') {
++cursor;
}
// We expect at least four letters for flags (ex. "r-xp").
if (cursor == eol || cursor < flags_start + 4) {
ABSL_RAW_LOG(WARNING, "Corrupt /proc/self/maps: %s", line);
return false;
}
// Check flags.
if (!ShouldUseMapping(flags_start)) {
continue; // We skip this map.
}
++cursor; // Skip ' '.
// Read file offset.
uint64_t offset;
cursor = GetHex(cursor, eol, &offset);
++cursor; // Skip ' '.
// Skip to file name. "cursor" now points to dev. We need to skip at least
// two spaces for dev and inode.
int num_spaces = 0;
while (cursor < eol) {
if (*cursor == ' ') {
++num_spaces;
} else if (num_spaces >= 2) {
// The first non-space character after skipping two spaces
// is the beginning of the file name.
break;
}
++cursor;
}
// Check whether this entry corresponds to our hint table for the true
// filename.
bool hinted =
GetFileMappingHint(&start_address, &end_address, &offset, &cursor);
if (!hinted && (cursor == eol || cursor[0] == '[')) {
// not an object file, typically [vdso] or [vsyscall]
continue;
}
if (!callback(cursor, start_address, end_address, offset, arg)) break;
}
return true;
}
// Find the objfile mapped in address region containing [addr, addr + len).
ObjFile *Symbolizer::FindObjFile(const void *const addr, size_t len) {
for (int i = 0; i < 2; ++i) {
if (!ok_) return nullptr;
// Read /proc/self/maps if necessary
if (!addr_map_read_) {
addr_map_read_ = true;
if (!ReadAddrMap(RegisterObjFile, this, tmp_buf_, TMP_BUF_SIZE)) {
ok_ = false;
return nullptr;
}
}
size_t lo = 0;
size_t hi = addr_map_.Size();
while (lo < hi) {
size_t mid = (lo + hi) / 2;
if (addr < addr_map_.At(mid)->end_addr) {
hi = mid;
} else {
lo = mid + 1;
}
}
if (lo != addr_map_.Size()) {
ObjFile *obj = addr_map_.At(lo);
SAFE_ASSERT(obj->end_addr > addr);
if (addr >= obj->start_addr &&
reinterpret_cast<const char *>(addr) + len <= obj->end_addr)
return obj;
}
// The address mapping may have changed since it was last read. Retry.
ClearAddrMap();
}
return nullptr;
}
void Symbolizer::ClearAddrMap() {
for (size_t i = 0; i != addr_map_.Size(); i++) {
ObjFile *o = addr_map_.At(i);
base_internal::LowLevelAlloc::Free(o->filename);
if (o->fd >= 0) {
close(o->fd);
}
}
addr_map_.Clear();
addr_map_read_ = false;
}
// Callback for ReadAddrMap to register objfiles in an in-memory table.
bool Symbolizer::RegisterObjFile(const char *filename,
const void *const start_addr,
const void *const end_addr, uint64_t offset,
void *arg) {
Symbolizer *impl = static_cast<Symbolizer *>(arg);
// Files are supposed to be added in the increasing address order. Make
// sure that's the case.
size_t addr_map_size = impl->addr_map_.Size();
if (addr_map_size != 0) {
ObjFile *old = impl->addr_map_.At(addr_map_size - 1);
if (old->end_addr > end_addr) {
ABSL_RAW_LOG(ERROR,
"Unsorted addr map entry: 0x%" PRIxPTR ": %s <-> 0x%" PRIxPTR
": %s",
reinterpret_cast<uintptr_t>(end_addr), filename,
reinterpret_cast<uintptr_t>(old->end_addr), old->filename);
return true;
} else if (old->end_addr == end_addr) {
// The same entry appears twice. This sometimes happens for [vdso].
if (old->start_addr != start_addr ||
strcmp(old->filename, filename) != 0) {
ABSL_RAW_LOG(ERROR,
"Duplicate addr 0x%" PRIxPTR ": %s <-> 0x%" PRIxPTR ": %s",
reinterpret_cast<uintptr_t>(end_addr), filename,
reinterpret_cast<uintptr_t>(old->end_addr), old->filename);
}
return true;
} else if (old->end_addr == start_addr &&
reinterpret_cast<uintptr_t>(old->start_addr) - old->offset ==
reinterpret_cast<uintptr_t>(start_addr) - offset &&
strcmp(old->filename, filename) == 0) {
// Two contiguous map entries that span a contiguous region of the file,
// perhaps because some part of the file was mlock()ed. Combine them.
old->end_addr = end_addr;
return true;
}
}
ObjFile *obj = impl->addr_map_.Add();
obj->filename = impl->CopyString(filename);
obj->start_addr = start_addr;
obj->end_addr = end_addr;
obj->offset = offset;
obj->elf_type = -1; // filled on demand
obj->fd = -1; // opened on demand
return true;
}
// This function wraps the Demangle function to provide an interface
// where the input symbol is demangled in-place.
// To keep stack consumption low, we would like this function to not
// get inlined.
static ABSL_ATTRIBUTE_NOINLINE void DemangleInplace(char *out, size_t out_size,
char *tmp_buf,
size_t tmp_buf_size) {
if (Demangle(out, tmp_buf, tmp_buf_size)) {
// Demangling succeeded. Copy to out if the space allows.
size_t len = strlen(tmp_buf);
if (len + 1 <= out_size) { // +1 for '\0'.
SAFE_ASSERT(len < tmp_buf_size);
memmove(out, tmp_buf, len + 1);
}
}
}
SymbolCacheLine *Symbolizer::GetCacheLine(const void *const pc) {
uintptr_t pc0 = reinterpret_cast<uintptr_t>(pc);
pc0 >>= 3; // drop the low 3 bits
// Shuffle bits.
pc0 ^= (pc0 >> 6) ^ (pc0 >> 12) ^ (pc0 >> 18);
return &symbol_cache_[pc0 % SYMBOL_CACHE_LINES];
}
void Symbolizer::AgeSymbols(SymbolCacheLine *line) {
for (uint32_t &age : line->age) {
++age;
}
}
const char *Symbolizer::FindSymbolInCache(const void *const pc) {
if (pc == nullptr) return nullptr;
SymbolCacheLine *line = GetCacheLine(pc);
for (size_t i = 0; i < ABSL_ARRAYSIZE(line->pc); ++i) {
if (line->pc[i] == pc) {
AgeSymbols(line);
line->age[i] = 0;
return line->name[i];
}
}
return nullptr;
}
const char *Symbolizer::InsertSymbolInCache(const void *const pc,
const char *name) {
SAFE_ASSERT(pc != nullptr);
SymbolCacheLine *line = GetCacheLine(pc);
uint32_t max_age = 0;
size_t oldest_index = 0;
bool found_oldest_index = false;
for (size_t i = 0; i < ABSL_ARRAYSIZE(line->pc); ++i) {
if (line->pc[i] == nullptr) {
AgeSymbols(line);
line->pc[i] = pc;
line->name[i] = CopyString(name);
line->age[i] = 0;
return line->name[i];
}
if (line->age[i] >= max_age) {
max_age = line->age[i];
oldest_index = i;
found_oldest_index = true;
}
}
AgeSymbols(line);
ABSL_RAW_CHECK(found_oldest_index, "Corrupt cache");
base_internal::LowLevelAlloc::Free(line->name[oldest_index]);
line->pc[oldest_index] = pc;
line->name[oldest_index] = CopyString(name);
line->age[oldest_index] = 0;
return line->name[oldest_index];
}
static void MaybeOpenFdFromSelfExe(ObjFile *obj) {
if (memcmp(obj->start_addr, ELFMAG, SELFMAG) != 0) {
return;
}
int fd = open("/proc/self/exe", O_RDONLY);
if (fd == -1) {
return;
}
// Verify that contents of /proc/self/exe matches in-memory image of
// the binary. This can fail if the "deleted" binary is in fact not
// the main executable, or for binaries that have the first PT_LOAD
// segment smaller than 4K. We do it in four steps so that the
// buffer is smaller and we don't consume too much stack space.
const char *mem = reinterpret_cast<const char *>(obj->start_addr);
for (int i = 0; i < 4; ++i) {
char buf[1024];
ssize_t n = read(fd, buf, sizeof(buf));
if (n != sizeof(buf) || memcmp(buf, mem, sizeof(buf)) != 0) {
close(fd);
return;
}
mem += sizeof(buf);
}
obj->fd = fd;
}
static bool MaybeInitializeObjFile(ObjFile *obj) {
if (obj->fd < 0) {
obj->fd = open(obj->filename, O_RDONLY);
if (obj->fd < 0) {
// Getting /proc/self/exe here means that we were hinted.
if (strcmp(obj->filename, "/proc/self/exe") == 0) {
// /proc/self/exe may be inaccessible (due to setuid, etc.), so try
// accessing the binary via argv0.
if (argv0_value != nullptr) {
obj->fd = open(argv0_value, O_RDONLY);
}
} else {
MaybeOpenFdFromSelfExe(obj);
}
}
if (obj->fd < 0) {
ABSL_RAW_LOG(WARNING, "%s: open failed: errno=%d", obj->filename, errno);
return false;
}
obj->elf_type = FileGetElfType(obj->fd);
if (obj->elf_type < 0) {
ABSL_RAW_LOG(WARNING, "%s: wrong elf type: %d", obj->filename,
obj->elf_type);
return false;
}
if (!ReadFromOffsetExact(obj->fd, &obj->elf_header, sizeof(obj->elf_header),
0)) {
ABSL_RAW_LOG(WARNING, "%s: failed to read elf header", obj->filename);
return false;
}
const int phnum = obj->elf_header.e_phnum;
const int phentsize = obj->elf_header.e_phentsize;
auto phoff = static_cast<off_t>(obj->elf_header.e_phoff);
size_t num_interesting_load_segments = 0;
for (int j = 0; j < phnum; j++) {
ElfW(Phdr) phdr;
if (!ReadFromOffsetExact(obj->fd, &phdr, sizeof(phdr), phoff)) {
ABSL_RAW_LOG(WARNING, "%s: failed to read program header %d",
obj->filename, j);
return false;
}
phoff += phentsize;
#if defined(__powerpc__) && !(_CALL_ELF > 1)
// On the PowerPC ELF v1 ABI, function pointers actually point to function
// descriptors. These descriptors are stored in an .opd section, which is
// mapped read-only. We thus need to look at all readable segments, not
// just the executable ones.
constexpr int interesting = PF_R;
#else
constexpr int interesting = PF_X | PF_R;
#endif
if (phdr.p_type != PT_LOAD
|| (phdr.p_flags & interesting) != interesting) {
// Not a LOAD segment, not executable code, and not a function
// descriptor.
continue;
}
if (num_interesting_load_segments < obj->phdr.size()) {
memcpy(&obj->phdr[num_interesting_load_segments++], &phdr, sizeof(phdr));
} else {
ABSL_RAW_LOG(
WARNING, "%s: too many interesting LOAD segments: %zu >= %zu",
obj->filename, num_interesting_load_segments, obj->phdr.size());
break;
}
}
if (num_interesting_load_segments == 0) {
// This object has no interesting LOAD segments. That's unexpected.
ABSL_RAW_LOG(WARNING, "%s: no interesting LOAD segments", obj->filename);
return false;
}
}
return true;
}
// The implementation of our symbolization routine. If it
// successfully finds the symbol containing "pc" and obtains the
// symbol name, returns pointer to that symbol. Otherwise, returns nullptr.
// If any symbol decorators have been installed via InstallSymbolDecorator(),
// they are called here as well.
// To keep stack consumption low, we would like this function to not
// get inlined.
const char *Symbolizer::GetUncachedSymbol(const void *pc) {
ObjFile *const obj = FindObjFile(pc, 1);
ptrdiff_t relocation = 0;
int fd = -1;
if (obj != nullptr) {
if (MaybeInitializeObjFile(obj)) {
const size_t start_addr = reinterpret_cast<size_t>(obj->start_addr);
if (obj->elf_type == ET_DYN && start_addr >= obj->offset) {
// This object was relocated.
//
// For obj->offset > 0, adjust the relocation since a mapping at offset
// X in the file will have a start address of [true relocation]+X.
relocation = static_cast<ptrdiff_t>(start_addr - obj->offset);
// Note: some binaries have multiple LOAD segments that can contain
// function pointers. We must find the right one.
ElfW(Phdr) *phdr = nullptr;
for (size_t j = 0; j < obj->phdr.size(); j++) {
ElfW(Phdr) &p = obj->phdr[j];
if (p.p_type != PT_LOAD) {
// We only expect PT_LOADs. This must be PT_NULL that we didn't
// write over (i.e. we exhausted all interesting PT_LOADs).
ABSL_RAW_CHECK(p.p_type == PT_NULL, "unexpected p_type");
break;
}
if (pc < reinterpret_cast<void *>(start_addr + p.p_vaddr + p.p_memsz)) {
phdr = &p;
break;
}
}
if (phdr == nullptr) {
// That's unexpected. Hope for the best.
ABSL_RAW_LOG(
WARNING,
"%s: unable to find LOAD segment for pc: %p, start_addr: %zx",
obj->filename, pc, start_addr);
} else {
// Adjust relocation in case phdr.p_vaddr != 0.
// This happens for binaries linked with `lld --rosegment`, and for
// binaries linked with BFD `ld -z separate-code`.
relocation -= phdr->p_vaddr - phdr->p_offset;
}
}
fd = obj->fd;
if (GetSymbolFromObjectFile(*obj, pc, relocation, symbol_buf_,
sizeof(symbol_buf_), tmp_buf_,
sizeof(tmp_buf_)) == SYMBOL_FOUND) {
// Only try to demangle the symbol name if it fit into symbol_buf_.
DemangleInplace(symbol_buf_, sizeof(symbol_buf_), tmp_buf_,
sizeof(tmp_buf_));
}
}
} else {
#if ABSL_HAVE_VDSO_SUPPORT
VDSOSupport vdso;
if (vdso.IsPresent()) {
VDSOSupport::SymbolInfo symbol_info;
if (vdso.LookupSymbolByAddress(pc, &symbol_info)) {
// All VDSO symbols are known to be short.
size_t len = strlen(symbol_info.name);
ABSL_RAW_CHECK(len + 1 < sizeof(symbol_buf_),
"VDSO symbol unexpectedly long");
memcpy(symbol_buf_, symbol_info.name, len + 1);
}
}
#endif
}
if (g_decorators_mu.TryLock()) {
if (g_num_decorators > 0) {
SymbolDecoratorArgs decorator_args = {
pc, relocation, fd, symbol_buf_, sizeof(symbol_buf_),
tmp_buf_, sizeof(tmp_buf_), nullptr};
for (int i = 0; i < g_num_decorators; ++i) {
decorator_args.arg = g_decorators[i].arg;
g_decorators[i].fn(&decorator_args);
}
}
g_decorators_mu.Unlock();
}
if (symbol_buf_[0] == '\0') {
return nullptr;
}
symbol_buf_[sizeof(symbol_buf_) - 1] = '\0'; // Paranoia.
return InsertSymbolInCache(pc, symbol_buf_);
}
const char *Symbolizer::GetSymbol(const void *pc) {
const char *entry = FindSymbolInCache(pc);
if (entry != nullptr) {
return entry;
}
symbol_buf_[0] = '\0';
#ifdef __hppa__
{
// In some contexts (e.g., return addresses), PA-RISC uses the lowest two
// bits of the address to indicate the privilege level. Clear those bits
// before trying to symbolize.
const auto pc_bits = reinterpret_cast<uintptr_t>(pc);
const auto address = pc_bits & ~0x3;
entry = GetUncachedSymbol(reinterpret_cast<const void *>(address));
if (entry != nullptr) {
return entry;
}
// In some contexts, PA-RISC also uses bit 1 of the address to indicate that
// this is a cross-DSO function pointer. Such function pointers actually
// point to a procedure label, a struct whose first 32-bit (pointer) element
// actually points to the function text. With no symbol found for this
// address so far, try interpreting it as a cross-DSO function pointer and
// see how that goes.
if (pc_bits & 0x2) {
return GetUncachedSymbol(*reinterpret_cast<const void *const *>(address));
}
return nullptr;
}
#else
return GetUncachedSymbol(pc);
#endif
}
bool RemoveAllSymbolDecorators(void) {
if (!g_decorators_mu.TryLock()) {
// Someone else is using decorators. Get out.
return false;
}
g_num_decorators = 0;
g_decorators_mu.Unlock();
return true;
}
bool RemoveSymbolDecorator(int ticket) {
if (!g_decorators_mu.TryLock()) {
// Someone else is using decorators. Get out.
return false;
}
for (int i = 0; i < g_num_decorators; ++i) {
if (g_decorators[i].ticket == ticket) {
while (i < g_num_decorators - 1) {
g_decorators[i] = g_decorators[i + 1];
++i;
}
g_num_decorators = i;
break;
}
}
g_decorators_mu.Unlock();
return true; // Decorator is known to be removed.
}
int InstallSymbolDecorator(SymbolDecorator decorator, void *arg) {
static int ticket = 0;
if (!g_decorators_mu.TryLock()) {
// Someone else is using decorators. Get out.
return -2;
}
int ret = ticket;
if (g_num_decorators >= kMaxDecorators) {
ret = -1;
} else {
g_decorators[g_num_decorators] = {decorator, arg, ticket++};
++g_num_decorators;
}
g_decorators_mu.Unlock();
return ret;
}
bool RegisterFileMappingHint(const void *start, const void *end, uint64_t offset,
const char *filename) {
SAFE_ASSERT(start <= end);
SAFE_ASSERT(filename != nullptr);
InitSigSafeArena();
if (!g_file_mapping_mu.TryLock()) {
return false;
}
bool ret = true;
if (g_num_file_mapping_hints >= kMaxFileMappingHints) {
ret = false;
} else {
// TODO(ckennelly): Move this into a string copy routine.
size_t len = strlen(filename);
char *dst = static_cast<char *>(
base_internal::LowLevelAlloc::AllocWithArena(len + 1, SigSafeArena()));
ABSL_RAW_CHECK(dst != nullptr, "out of memory");
memcpy(dst, filename, len + 1);
auto &hint = g_file_mapping_hints[g_num_file_mapping_hints++];
hint.start = start;
hint.end = end;
hint.offset = offset;
hint.filename = dst;
}
g_file_mapping_mu.Unlock();
return ret;
}
bool GetFileMappingHint(const void **start, const void **end, uint64_t *offset,
const char **filename) {
if (!g_file_mapping_mu.TryLock()) {
return false;
}
bool found = false;
for (int i = 0; i < g_num_file_mapping_hints; i++) {
if (g_file_mapping_hints[i].start <= *start &&
*end <= g_file_mapping_hints[i].end) {
// We assume that the start_address for the mapping is the base
// address of the ELF section, but when [start_address,end_address) is
// not strictly equal to [hint.start, hint.end), that assumption is
// invalid.
//
// This uses the hint's start address (even though hint.start is not
// necessarily equal to start_address) to ensure the correct
// relocation is computed later.
*start = g_file_mapping_hints[i].start;
*end = g_file_mapping_hints[i].end;
*offset = g_file_mapping_hints[i].offset;
*filename = g_file_mapping_hints[i].filename;
found = true;
break;
}
}
g_file_mapping_mu.Unlock();
return found;
}
} // namespace debugging_internal
bool Symbolize(const void *pc, char *out, int out_size) {
// Symbolization is very slow under tsan.
ABSL_ANNOTATE_IGNORE_READS_AND_WRITES_BEGIN();
SAFE_ASSERT(out_size >= 0);
debugging_internal::Symbolizer *s = debugging_internal::AllocateSymbolizer();
const char *name = s->GetSymbol(pc);
bool ok = false;
if (name != nullptr && out_size > 0) {
strncpy(out, name, static_cast<size_t>(out_size));
ok = true;
if (out[static_cast<size_t>(out_size) - 1] != '\0') {
// strncpy() does not '\0' terminate when it truncates. Do so, with
// trailing ellipsis.
static constexpr char kEllipsis[] = "...";
size_t ellipsis_size =
std::min(strlen(kEllipsis), static_cast<size_t>(out_size) - 1);
memcpy(out + static_cast<size_t>(out_size) - ellipsis_size - 1, kEllipsis,
ellipsis_size);
out[static_cast<size_t>(out_size) - 1] = '\0';
}
}
debugging_internal::FreeSymbolizer(s);
ABSL_ANNOTATE_IGNORE_READS_AND_WRITES_END();
return ok;
}
ABSL_NAMESPACE_END
} // namespace absl
extern "C" bool AbslInternalGetFileMappingHint(const void **start,
const void **end, uint64_t *offset,
const char **filename) {
return absl::debugging_internal::GetFileMappingHint(start, end, offset,
filename);
}