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// Copyright (c) Meta Platforms, Inc. and affiliates.
// All rights reserved.
//
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree.
#pragma once
#include <c10/util/error.h>
#include <elf.h>
#include <fcntl.h>
#include <fmt/format.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <torch/csrc/profiler/unwind/lexer.h>
#include <torch/csrc/profiler/unwind/unwind_error.h>
#include <unistd.h>
#include <cerrno>
#include <cstdio>
#include <cstring>
namespace torch::unwind {
struct Section {
char* data = nullptr;
size_t size = 0;
const char* string(size_t offset) {
return lexer(offset).readCString();
}
CheckedLexer lexer(size_t offset) {
return CheckedLexer(data + offset, data, data + size);
}
};
/// Memory maps a file into the address space read-only, and manages the
/// lifetime of the mapping. Here are a few use cases:
/// 1. Used in the loader to read in initial image, and to inspect
// ELF files for dependencies before callling dlopen.
///
/// 2. Used in unity to load the elf file.
struct MemFile {
explicit MemFile(const char* filename_)
: fd_(open(filename_, O_RDONLY)), name_(filename_) {
UNWIND_CHECK(
fd_ != -1,
"failed to open {}: {}",
filename_,
c10::utils::str_error(errno));
struct stat s {};
if (-1 == fstat(fd_, &s)) {
close(fd_); // destructors don't run during exceptions
UNWIND_CHECK(
false,
"failed to stat {}: {}",
filename_,
c10::utils::str_error(errno));
}
n_bytes_ = s.st_size;
UNWIND_CHECK(
n_bytes_ > sizeof(Elf64_Ehdr), "empty shared library: {}", filename_);
mem_ = (char*)mmap(nullptr, n_bytes_, PROT_READ, MAP_SHARED, fd_, 0);
if (MAP_FAILED == mem_) {
close(fd_);
UNWIND_CHECK(
false,
"failed to mmap {}: {}",
filename_,
c10::utils::str_error(errno));
}
ehdr_ = (Elf64_Ehdr*)mem_;
#define ELF_CHECK(cond) UNWIND_CHECK(cond, "not an ELF file: {}", filename_)
ELF_CHECK(ehdr_->e_ident[EI_MAG0] == ELFMAG0);
ELF_CHECK(ehdr_->e_ident[EI_MAG1] == ELFMAG1);
ELF_CHECK(ehdr_->e_ident[EI_MAG2] == ELFMAG2);
ELF_CHECK(ehdr_->e_ident[EI_MAG3] == ELFMAG3);
ELF_CHECK(ehdr_->e_ident[EI_CLASS] == ELFCLASS64);
ELF_CHECK(ehdr_->e_ident[EI_VERSION] == EV_CURRENT);
ELF_CHECK(ehdr_->e_version == EV_CURRENT);
ELF_CHECK(ehdr_->e_machine == EM_X86_64);
#undef ELF_CHECK
UNWIND_CHECK(
ehdr_->e_shoff + sizeof(Elf64_Shdr) * ehdr_->e_shnum <= n_bytes_,
"invalid section header table {} {} {}",
ehdr_->e_shoff + sizeof(Elf64_Shdr) * ehdr_->e_shnum,
n_bytes_,
ehdr_->e_shnum);
shdr_ = (Elf64_Shdr*)(mem_ + ehdr_->e_shoff);
UNWIND_CHECK(
ehdr_->e_shstrndx < ehdr_->e_shnum, "invalid strtab section offset");
auto& strtab_hdr = shdr_[ehdr_->e_shstrndx];
strtab_ = getSection(strtab_hdr);
}
MemFile(const MemFile&) = delete;
MemFile(MemFile&&) = delete;
MemFile& operator=(const MemFile&) = delete;
MemFile& operator=(MemFile&&) = delete;
[[nodiscard]] const char* data() const {
return (const char*)mem_;
}
/// Returns whether or not the file descriptor
/// of the underlying file is valid.
int valid() {
return fcntl(fd_, F_GETFD) != -1 || errno != EBADF;
}
~MemFile() {
if (mem_) {
munmap((void*)mem_, n_bytes_);
}
if (fd_ >= 0) {
close(fd_);
}
}
/// Returns the size of the underlying file defined by the `MemFile`
size_t size() {
return n_bytes_;
}
[[nodiscard]] int fd() const {
return fd_;
}
Section getSection(const Elf64_Shdr& shdr) {
UNWIND_CHECK(shdr.sh_offset + shdr.sh_size <= n_bytes_, "invalid section");
return Section{mem_ + shdr.sh_offset, shdr.sh_size};
}
Section getSection(const char* name, bool optional) {
for (int i = 0; i < ehdr_->e_shnum; i++) {
if (strcmp(strtab_.string(shdr_[i].sh_name), name) == 0) {
return getSection(shdr_[i]);
}
}
UNWIND_CHECK(optional, "{} has no section {}", name_, name);
return Section{nullptr, 0};
}
Section strtab() {
return strtab_;
}
private:
template <typename T>
T* load(size_t offset) {
UNWIND_CHECK(offset < n_bytes_, "out of range");
return (T*)(mem_ + offset);
}
int fd_;
char* mem_{nullptr};
size_t n_bytes_{0};
std::string name_;
Elf64_Ehdr* ehdr_;
Elf64_Shdr* shdr_;
Section strtab_ = {nullptr, 0};
};
} // namespace torch::unwind
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