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Diffstat (limited to 'absl/debugging/symbolize_elf.inc')
| -rw-r--r-- | absl/debugging/symbolize_elf.inc | 1473 |
1 files changed, 1473 insertions, 0 deletions
diff --git a/absl/debugging/symbolize_elf.inc b/absl/debugging/symbolize_elf.inc new file mode 100644 index 000000000000..e21439ce3fac --- /dev/null +++ b/absl/debugging/symbolize_elf.inc @@ -0,0 +1,1473 @@ +// 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 +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// 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 <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" + +namespace absl { + +// Value of argv[0]. Used by MaybeInitializeObjFile(). +static char *argv0_value = nullptr; + +void InitializeSymbolizer(const char *argv0) { + 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. +base_internal::SpinLock g_decorators_mu(base_internal::kLinkerInitialized); + +const int kMaxFileMappingHints = 8; +int g_num_file_mapping_hints; +FileMappingHint g_file_mapping_hints[kMaxFileMappingHints]; +// Protects g_file_mapping_hints. +base_internal::SpinLock g_file_mapping_mu(base_internal::kLinkerInitialized); + +// 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)); + } + + 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; +}; + +// 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_); } + int Size() const { return size_; } + ObjFile *At(int i) { return &obj_[i]; } + ObjFile *Add(); + void Clear(); + + private: + int size_; // count of valid elements (<= allocated_) + int allocated_; // count of allocated elements + ObjFile *obj_; // array of allocated_ elements + AddrMap(const AddrMap &) = delete; + AddrMap &operator=(const AddrMap &) = delete; +}; + +void AddrMap::Clear() { + for (int i = 0; i != size_; i++) { + At(i)->~ObjFile(); + } + size_ = 0; +} + +ObjFile *AddrMap::Add() { + if (size_ == allocated_) { + int 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) { + int 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, int out_size, + char *tmp_buf, int tmp_buf_size); + + enum { + SYMBOL_BUF_SIZE = 2048, + 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 int SymbolizerSize() { + int pagesize = getpagesize(); + 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 += 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, %ju, SEEK_SET) failed: errno=%d", fd, + static_cast<uintmax_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, int tmp_buf_size) { + ElfW(Shdr) *buf = reinterpret_cast<ElfW(Shdr) *>(tmp_buf); + const int buf_entries = tmp_buf_size / sizeof(buf[0]); + const int buf_bytes = buf_entries * sizeof(buf[0]); + + for (int i = 0; i < sh_num;) { + const ssize_t num_bytes_left = (sh_num - i) * sizeof(buf[0]); + const ssize_t num_bytes_to_read = + (buf_bytes > num_bytes_left) ? num_bytes_left : buf_bytes; + const off_t offset = sh_offset + i * sizeof(buf[0]); + const ssize_t len = ReadFromOffset(fd, buf, num_bytes_to_read, offset); + if (len % sizeof(buf[0]) != 0) { + ABSL_RAW_LOG( + WARNING, + "Reading %zd bytes from offset %ju returned %zd which is not a " + "multiple of %zu.", + num_bytes_to_read, static_cast<uintmax_t>(offset), len, + sizeof(buf[0])); + return false; + } + const ssize_t num_headers_in_buf = len / sizeof(buf[0]); + SAFE_ASSERT(num_headers_in_buf <= buf_entries); + for (int 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(const std::string &name, + const ElfW(Shdr) &)> &callback) { + ElfW(Ehdr) elf_header; + if (!ReadFromOffsetExact(fd, &elf_header, sizeof(elf_header), 0)) { + return false; + } + + ElfW(Shdr) shstrtab; + off_t shstrtab_offset = + (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 = + (elf_header.e_shoff + elf_header.e_shentsize * i); + if (!ReadFromOffsetExact(fd, &out, sizeof(out), section_header_offset)) { + return false; + } + off_t name_offset = shstrtab.sh_offset + out.sh_name; + char header_name[kMaxSectionNameLen + 1]; + ssize_t n_read = + ReadFromOffset(fd, &header_name, kMaxSectionNameLen, name_offset); + if (n_read == -1) { + return false; + } else if (n_read > kMaxSectionNameLen) { + // Long read? + return false; + } + header_name[n_read] = '\0'; + + std::string name(header_name); + 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; + } + + ElfW(Shdr) shstrtab; + off_t shstrtab_offset = + (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 = + (elf_header.e_shoff + elf_header.e_shentsize * i); + if (!ReadFromOffsetExact(fd, out, sizeof(*out), section_header_offset)) { + return false; + } + off_t name_offset = 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, const ElfW(Shdr) * section) { + const char *start = reinterpret_cast<const char *>(section->sh_addr); + size_t size = static_cast<size_t>(section->sh_size); + return start <= address && address < (start + size); +} + +// 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, int out_size, + ptrdiff_t relocation, const ElfW(Shdr) * strtab, const ElfW(Shdr) * symtab, + const ElfW(Shdr) * opd, char *tmp_buf, int 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 int buf_entries = tmp_buf_size / sizeof(buf[0]); + + const int 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, 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 (int i = 0; i < num_symbols;) { + off_t offset = symtab->sh_offset + i * symtab->sh_entsize; + const int num_remaining_symbols = num_symbols - i; + const int entries_in_chunk = std::min(num_remaining_symbols, buf_entries); + const int bytes_in_chunk = entries_in_chunk * sizeof(buf[0]); + const ssize_t len = ReadFromOffset(fd, buf, bytes_in_chunk, offset); + SAFE_ASSERT(len % sizeof(buf[0]) == 0); + const ssize_t num_symbols_in_buf = len / sizeof(buf[0]); + SAFE_ASSERT(num_symbols_in_buf <= entries_in_chunk); + for (int 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 = original_start_address + relocation; + + if (deref_function_descriptor_pointer && + InSection(original_start_address, 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 = + reinterpret_cast<const char *>(start_address) + 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 size_t off = 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 %zu: n_read = %zd", fd, + off, n_read); + return SYMBOL_NOT_FOUND; + } + ABSL_RAW_CHECK(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', 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, int out_size, char *tmp_buf, int 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 first. + if (!GetSectionHeaderByType(obj.fd, obj.elf_header.e_shnum, + obj.elf_header.e_shoff, SHT_SYMTAB, &symtab, + tmp_buf, tmp_buf_size)) { + return SYMBOL_NOT_FOUND; + } + if (!ReadFromOffsetExact( + obj.fd, &strtab, sizeof(strtab), + obj.elf_header.e_shoff + symtab.sh_link * sizeof(symtab))) { + return SYMBOL_NOT_FOUND; + } + 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; // Found the symbol in a regular symbol table. + } + + // If the symbol is not found, then consult a dynamic symbol table. + if (!GetSectionHeaderByType(obj.fd, obj.elf_header.e_shnum, + obj.elf_header.e_shoff, SHT_DYNSYM, &symtab, + tmp_buf, tmp_buf_size)) { + return SYMBOL_NOT_FOUND; + } + if (!ReadFromOffsetExact( + obj.fd, &strtab, sizeof(strtab), + obj.elf_header.e_shoff + symtab.sh_link * sizeof(symtab))) { + return SYMBOL_NOT_FOUND; + } + return FindSymbol(pc, obj.fd, out, out_size, relocation, &strtab, &symtab, + opd_ptr, tmp_buf, tmp_buf_size); +} + +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) { + NO_INTR(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, int 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 int incomplete_line_length = 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 int 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', eod_ - bol_)); + } + + bool BufferIsEmpty() const { return buf_ == eod_; } + + bool HasCompleteLine() const { + return !BufferIsEmpty() && FindLineFeed() != nullptr; + } + + const int fd_; + const int 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) | (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; +} + +// 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, int 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. 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**". + if (memcmp(flags_start, "r-x", 3) != 0 && // Not a "r-x" map. + !(kPlatformUsesOPDSections && flags_start[0] == 'r')) { + 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; + } + } + + int lo = 0; + int hi = addr_map_.Size(); + while (lo < hi) { + int 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 (int i = 0; i != addr_map_.Size(); i++) { + ObjFile *o = addr_map_.At(i); + base_internal::LowLevelAlloc::Free(o->filename); + if (o->fd >= 0) { + NO_INTR(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. + int 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; + } + } + 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, int out_size, + char *tmp_buf, + int tmp_buf_size) { + if (Demangle(out, tmp_buf, tmp_buf_size)) { + // Demangling succeeded. Copy to out if the space allows. + int 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; + int oldest_index = -1; + 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; + } + } + + AgeSymbols(line); + ABSL_RAW_CHECK(oldest_index >= 0, "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; + } + } + 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::GetSymbol(const void *const pc) { + const char *entry = FindSymbolInCache(pc); + if (entry != nullptr) { + return entry; + } + symbol_buf_[0] = '\0'; + + ObjFile *const obj = FindObjFile(pc, 1); + ptrdiff_t relocation = 0; + int fd = -1; + if (obj != nullptr) { + if (MaybeInitializeObjFile(obj)) { + if (obj->elf_type == ET_DYN && + reinterpret_cast<uint64_t>(obj->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 = reinterpret_cast<ptrdiff_t>(obj->start_addr) - obj->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_); +} + +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 false; + } + 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 std::string copy routine. + int 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. + 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, out_size); + ok = true; + if (out[out_size - 1] != '\0') { + // strncpy() does not '\0' terminate when it truncates. Do so, with + // trailing ellipsis. + static constexpr char kEllipsis[] = "..."; + int ellipsis_size = + std::min(implicit_cast<int>(strlen(kEllipsis)), out_size - 1); + memcpy(out + out_size - ellipsis_size - 1, kEllipsis, ellipsis_size); + out[out_size - 1] = '\0'; + } + } + debugging_internal::FreeSymbolizer(s); + ANNOTATE_IGNORE_READS_AND_WRITES_END(); + return ok; +} + +} // namespace absl |