path: root/src/common/linux/dump_symbols.cc

// Copyright (c) 2006, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#include <elf.h>
#include <fcntl.h>
#include <link.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <unistd.h>

#include <cassert>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>

#include "common/linux/dump_stabs.h"
#include "common/linux/dump_symbols.h"
#include "common/linux/file_id.h"
#include "common/linux/module.h"
#include "common/linux/stabs_reader.h"

// This namespace contains helper functions.
namespace {

using google_breakpad::Module;
using google_breakpad::DumpStabsHandler;

// Stab section name.
static const char *kStabName = ".stab";

// Fix offset into virtual address by adding the mapped base into offsets.
// Make life easier when want to find something by offset.
static void FixAddress(void *obj_base) {
  ElfW(Addr) base = reinterpret_cast<ElfW(Addr)>(obj_base);
  ElfW(Ehdr) *elf_header = static_cast<ElfW(Ehdr) *>(obj_base);
  elf_header->e_phoff += base;
  elf_header->e_shoff += base;
  ElfW(Shdr) *sections = reinterpret_cast<ElfW(Shdr) *>(elf_header->e_shoff);
  for (int i = 0; i < elf_header->e_shnum; ++i)
    sections[i].sh_offset += base;
}

// Find the prefered loading address of the binary.
static ElfW(Addr) GetLoadingAddress(const ElfW(Phdr) *program_headers,
                                    int nheader) {
  for (int i = 0; i < nheader; ++i) {
    const ElfW(Phdr) &header = program_headers[i];
    // For executable, it is the PT_LOAD segment with offset to zero.
    if (header.p_type == PT_LOAD &&
        header.p_offset == 0)
      return header.p_vaddr;
  }
  // For other types of ELF, return 0.
  return 0;
}

static bool IsValidElf(const ElfW(Ehdr) *elf_header) {
  return memcmp(elf_header, ELFMAG, SELFMAG) == 0;
}

static const ElfW(Shdr) *FindSectionByName(const char *name,
                                           const ElfW(Shdr) *sections,
                                           const ElfW(Shdr) *strtab,
                                           int nsection) {
  assert(name != NULL);
  assert(sections != NULL);
  assert(nsection > 0);

  int name_len = strlen(name);
  if (name_len == 0)
    return NULL;

  for (int i = 0; i < nsection; ++i) {
    const char *section_name =
      reinterpret_cast<char*>(strtab->sh_offset + sections[i].sh_name);
    if (!strncmp(name, section_name, name_len))
      return sections + i;
  }
  return NULL;
}

static bool LoadSymbols(const ElfW(Shdr) *stab_section,
                        const ElfW(Shdr) *stabstr_section,
                        Module *module) {
  if (stab_section == NULL || stabstr_section == NULL)
    return false;

  // A callback object to handle data from the STABS reader.
  DumpStabsHandler handler(module);
  // Find the addresses of the STABS data, and create a STABS reader object.
  uint8_t *stabs = reinterpret_cast<uint8_t *>(stab_section->sh_offset);
  uint8_t *stabstr = reinterpret_cast<uint8_t *>(stabstr_section->sh_offset);
  google_breakpad::StabsReader reader(stabs, stab_section->sh_size,
                                      stabstr, stabstr_section->sh_size,
                                      &handler);
  // Read the STABS data, and do post-processing.
  if (! reader.Process())
    return false;
  handler.Finalize();
  return true;
}

static bool LoadSymbols(ElfW(Ehdr) *elf_header, Module *module) {
  // Translate all offsets in section headers into address.
  FixAddress(elf_header);
  ElfW(Addr) loading_addr = GetLoadingAddress(
      reinterpret_cast<ElfW(Phdr) *>(elf_header->e_phoff),
      elf_header->e_phnum);
  module->SetLoadAddress(loading_addr);

  const ElfW(Shdr) *sections =
    reinterpret_cast<ElfW(Shdr) *>(elf_header->e_shoff);
  const ElfW(Shdr) *strtab = sections + elf_header->e_shstrndx;
  const ElfW(Shdr) *stab_section =
    FindSectionByName(kStabName, sections, strtab, elf_header->e_shnum);
  if (stab_section == NULL) {
    fprintf(stderr, "Stab section not found.\n");
    return false;
  }
  const ElfW(Shdr) *stabstr_section = stab_section->sh_link + sections;

  // Load symbols.
  return LoadSymbols(stab_section, stabstr_section, module);
}

//
// FDWrapper
//
// Wrapper class to make sure opened file is closed.
//
class FDWrapper {
 public:
  explicit FDWrapper(int fd) :
    fd_(fd) {
    }
  ~FDWrapper() {
    if (fd_ != -1)
      close(fd_);
  }
  int get() {
    return fd_;
  }
  int release() {
    int fd = fd_;
    fd_ = -1;
    return fd;
  }
 private:
  int fd_;
};

//
// MmapWrapper
//
// Wrapper class to make sure mapped regions are unmapped.
//
class MmapWrapper {
  public:
   MmapWrapper(void *mapped_address, size_t mapped_size) :
     base_(mapped_address), size_(mapped_size) {
   }
   ~MmapWrapper() {
     if (base_ != NULL) {
       assert(size_ > 0);
       munmap(base_, size_);
     }
   }
   void release() {
     base_ = NULL;
     size_ = 0;
   }

  private:
   void *base_;
   size_t size_;
};

// Return the breakpad symbol file identifier for the architecture of
// ELF_HEADER.
const char *ElfArchitecture(const ElfW(Ehdr) *elf_header) {
  ElfW(Half) arch = elf_header->e_machine;
  if (arch == EM_386)
    return "x86";
  else if (arch == EM_X86_64)
    return "x86_64";
  else
    return NULL;
}

// Format the Elf file identifier in IDENTIFIER as a UUID with the
// dashes removed.
std::string FormatIdentifier(unsigned char identifier[16]) {
  char identifier_str[40];
  google_breakpad::FileID::ConvertIdentifierToString(
      identifier,
      identifier_str,
      sizeof(identifier_str));
  std::string id_no_dash;
  for (int i = 0; identifier_str[i] != '\0'; ++i)
    if (identifier_str[i] != '-')
      id_no_dash += identifier_str[i];
  // Add an extra "0" by the end.  PDB files on Windows have an 'age'
  // number appended to the end of the file identifier; this isn't
  // really used or necessary on other platforms, but let's preserve
  // the pattern.
  id_no_dash += '0';
  return id_no_dash;
}

// Return the non-directory portion of FILENAME: the portion after the
// last slash, or the whole filename if there are no slashes.
std::string BaseFileName(const std::string &filename) {
  // Lots of copies!  basename's behavior is less than ideal.
  char *c_filename = strdup(filename.c_str());
  std::string base = basename(c_filename);
  free(c_filename);
  return base;
}

}  // namespace

namespace google_breakpad {

bool DumpSymbols::WriteSymbolFile(const std::string &obj_file,
                                  FILE *sym_file) {
  int obj_fd = open(obj_file.c_str(), O_RDONLY);
  if (obj_fd < 0)
    return false;
  FDWrapper obj_fd_wrapper(obj_fd);
  struct stat st;
  if (fstat(obj_fd, &st) != 0 && st.st_size <= 0)
    return false;
  void *obj_base = mmap(NULL, st.st_size,
                        PROT_READ | PROT_WRITE, MAP_PRIVATE, obj_fd, 0);
  if (obj_base == MAP_FAILED)
    return false;
  MmapWrapper map_wrapper(obj_base, st.st_size);
  ElfW(Ehdr) *elf_header = reinterpret_cast<ElfW(Ehdr) *>(obj_base);
  if (!IsValidElf(elf_header))
    return false;

  unsigned char identifier[16];
  google_breakpad::FileID file_id(obj_file.c_str());
  if (! file_id.ElfFileIdentifier(identifier))
    return false;

  const char *architecture = ElfArchitecture(elf_header);
  if (! architecture)
    return false;

  std::string name = BaseFileName(obj_file);
  std::string os = "Linux";
  std::string id = FormatIdentifier(identifier);

  Module module(name, os, architecture, id);
  if (!LoadSymbols(elf_header, &module))
    return false;
  if (!module.Write(sym_file))
    return false;

  return true;
}

}  // namespace google_breakpad