base/sampling_heap_profiler/module_cache_mac.cc

// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/sampling_heap_profiler/module_cache.h"

#include <dlfcn.h>
#include <mach-o/getsect.h>
#include <uuid/uuid.h>

#include "base/strings/string_number_conversions.h"
#include "starboard/types.h"

namespace base {

namespace {

// Returns the unique build ID for a module loaded at |module_addr|. Returns the
// empty string if the function fails to get the build ID.
//
// Build IDs are created by the concatenation of the module's GUID (Windows) /
// UUID (Mac) and an "age" field that indicates how many times that GUID/UUID
// has been reused. In Windows binaries, the "age" field is present in the
// module header, but on the Mac, UUIDs are never reused and so the "age" value
// appended to the UUID is always 0.
std::string GetUniqueId(const void* module_addr) {
  const mach_header_64* mach_header =
      reinterpret_cast<const mach_header_64*>(module_addr);
  DCHECK_EQ(MH_MAGIC_64, mach_header->magic);

  size_t offset = sizeof(mach_header_64);
  size_t offset_limit = sizeof(mach_header_64) + mach_header->sizeofcmds;

  for (uint32_t i = 0; i < mach_header->ncmds; ++i) {
    if (offset + sizeof(load_command) >= offset_limit)
      return std::string();

    const load_command* current_cmd = reinterpret_cast<const load_command*>(
        reinterpret_cast<const uint8_t*>(mach_header) + offset);

    if (offset + current_cmd->cmdsize > offset_limit) {
      // This command runs off the end of the command list. This is malformed.
      return std::string();
    }

    if (current_cmd->cmd == LC_UUID) {
      if (current_cmd->cmdsize < sizeof(uuid_command)) {
        // This "UUID command" is too small. This is malformed.
        return std::string();
      }

      const uuid_command* uuid_cmd =
          reinterpret_cast<const uuid_command*>(current_cmd);
      static_assert(sizeof(uuid_cmd->uuid) == sizeof(uuid_t),
                    "UUID field of UUID command should be 16 bytes.");
      // The ID is comprised of the UUID concatenated with the Mac's "age" value
      // which is always 0.
      return HexEncode(&uuid_cmd->uuid, sizeof(uuid_cmd->uuid)) + "0";
    }
    offset += current_cmd->cmdsize;
  }
  return std::string();
}

}  // namespace

// static
ModuleCache::Module ModuleCache::CreateModuleForAddress(uintptr_t address) {
  Dl_info inf;
  if (!dladdr(reinterpret_cast<const void*>(address), &inf))
    return Module();
  auto base_module_address = reinterpret_cast<uintptr_t>(inf.dli_fbase);
  return Module(base_module_address, GetUniqueId(inf.dli_fbase),
                FilePath(inf.dli_fname), GetModuleTextSize(inf.dli_fbase));
}

size_t ModuleCache::GetModuleTextSize(const void* module_addr) {
  const mach_header_64* mach_header =
      reinterpret_cast<const mach_header_64*>(module_addr);
  DCHECK_EQ(MH_MAGIC_64, mach_header->magic);
  unsigned long module_size;
  getsegmentdata(mach_header, SEG_TEXT, &module_size);
  return module_size;
}

}  // namespace base