path: root/breakpad/linux/minidump_writer.cc

// Copyright (c) 2009, 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.

// This code writes out minidump files:
//   http://msdn.microsoft.com/en-us/library/ms680378(VS.85,loband).aspx
//
// Minidumps are a Microsoft format which Breakpad uses for recording crash
// dumps. This code has to run in a compromised environment (the address space
// may have received SIGSEGV), thus the following rules apply:
//   * You may not enter the dynamic linker. This means that we cannot call
//     any symbols in a shared library (inc libc). Because of this we replace
//     libc functions in linux_libc_support.h.
//   * You may not call syscalls via the libc wrappers. This rule is a subset
//     of the first rule but it bears repeating. We have direct wrappers
//     around the system calls in linux_syscall_support.h.
//   * You may not malloc. There's an alternative allocator in memory.h and
//     a canonical instance in the LinuxDumper object. We use the placement
//     new form to allocate objects and we don't delete them.

#include "breakpad/linux/minidump_writer.h"
#include "client/minidump_file_writer-inl.h"

#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ucontext.h>
#include <sys/user.h>

#include "client/minidump_file_writer.h"
#include "google_breakpad/common/minidump_format.h"
#include "google_breakpad/common/minidump_cpu_amd64.h"
#include "google_breakpad/common/minidump_cpu_x86.h"

#include "breakpad/linux/exception_handler.h"
#include "breakpad/linux/linux_dumper.h"
#include "breakpad/linux/linux_libc_support.h"
#include "breakpad/linux/linux_syscall_support.h"
#include "breakpad/linux/minidump_format_linux.h"

// Minidump defines register structures which are different from the raw
// structures which we get from the kernel. These are platform specific
// functions to juggle the ucontext and user structures into minidump format.
#if defined(__i386)
typedef MDRawContextX86 RawContextCPU;

// Write a uint16_t to memory
//   out: memory location to write to
//   v: value to write.
static void U16(void* out, uint16_t v) {
  memcpy(out, &v, sizeof(v));
}

// Write a uint32_t to memory
//   out: memory location to write to
//   v: value to write.
static void U32(void* out, uint32_t v) {
  memcpy(out, &v, sizeof(v));
}

// Juggle an x86 user_(fp|fpx|)regs_struct into minidump format
//   out: the minidump structure
//   info: the collection of register structures.
static void CPUFillFromThreadInfo(MDRawContextX86 *out,
                                  const google_breakpad::ThreadInfo &info) {
  out->context_flags = MD_CONTEXT_X86_ALL;

  out->dr0 = info.dregs[0];
  out->dr1 = info.dregs[1];
  out->dr2 = info.dregs[2];
  out->dr3 = info.dregs[3];
  // 4 and 5 deliberatly omitted because they aren't included in the minidump
  // format.
  out->dr6 = info.dregs[6];
  out->dr7 = info.dregs[7];

  out->gs = info.regs.xgs;
  out->fs = info.regs.xfs;
  out->es = info.regs.xes;
  out->ds = info.regs.xds;

  out->edi = info.regs.edi;
  out->esi = info.regs.esi;
  out->ebx = info.regs.ebx;
  out->edx = info.regs.edx;
  out->ecx = info.regs.ecx;
  out->eax = info.regs.eax;

  out->ebp = info.regs.ebp;
  out->eip = info.regs.eip;
  out->cs = info.regs.xcs;
  out->eflags = info.regs.eflags;
  out->esp = info.regs.esp;
  out->ss = info.regs.xss;

  out->float_save.control_word = info.fpregs.cwd;
  out->float_save.status_word = info.fpregs.swd;
  out->float_save.tag_word = info.fpregs.twd;
  out->float_save.error_offset = info.fpregs.fip;
  out->float_save.error_selector = info.fpregs.fcs;
  out->float_save.data_offset = info.fpregs.foo;
  out->float_save.data_selector = info.fpregs.fos;

  // 8 registers * 10 bytes per register.
  memcpy(out->float_save.register_area, info.fpregs.st_space, 10 * 8);

  // This matches the Intel fpsave format.
  U16(out->extended_registers + 0, info.fpregs.cwd);
  U16(out->extended_registers + 2, info.fpregs.swd);
  U16(out->extended_registers + 4, info.fpregs.twd);
  U16(out->extended_registers + 6, info.fpxregs.fop);
  U32(out->extended_registers + 8, info.fpxregs.fip);
  U16(out->extended_registers + 12, info.fpxregs.fcs);
  U32(out->extended_registers + 16, info.fpregs.foo);
  U16(out->extended_registers + 20, info.fpregs.fos);
  U32(out->extended_registers + 24, info.fpxregs.mxcsr);

  memcpy(out->extended_registers + 32, &info.fpxregs.st_space, 128);
  memcpy(out->extended_registers + 160, &info.fpxregs.xmm_space, 128);
}

// Juggle an x86 ucontext into minidump format
//   out: the minidump structure
//   info: the collection of register structures.
static void CPUFillFromUContext(MDRawContextX86 *out, const ucontext *uc,
                                const struct _libc_fpstate* fp) {
  const greg_t* regs = uc->uc_mcontext.gregs;

  out->context_flags = MD_CONTEXT_X86_FULL |
                       MD_CONTEXT_X86_FLOATING_POINT;

  out->gs = regs[REG_GS];
  out->fs = regs[REG_FS];
  out->es = regs[REG_ES];
  out->ds = regs[REG_DS];

  out->edi = regs[REG_EDI];
  out->esi = regs[REG_ESI];
  out->ebx = regs[REG_EBX];
  out->edx = regs[REG_EDX];
  out->ecx = regs[REG_ECX];
  out->eax = regs[REG_EAX];

  out->ebp = regs[REG_EBP];
  out->eip = regs[REG_EIP];
  out->cs = regs[REG_CS];
  out->eflags = regs[REG_EFL];
  out->esp = regs[REG_UESP];
  out->ss = regs[REG_SS];

  out->float_save.control_word = fp->cw;
  out->float_save.status_word = fp->sw;
  out->float_save.tag_word = fp->tag;
  out->float_save.error_offset = fp->ipoff;
  out->float_save.error_selector = fp->cssel;
  out->float_save.data_offset = fp->dataoff;
  out->float_save.data_selector = fp->datasel;

  // 8 registers * 10 bytes per register.
  memcpy(out->float_save.register_area, fp->_st, 10 * 8);
}

#elif defined(__x86_64)
typedef MDRawContextAMD64 RawContextCPU;

static void CPUFillFromThreadInfo(MDRawContextAMD64 *out,
                                  const google_breakpad::ThreadInfo &info) {
  out->context_flags = MD_CONTEXT_AMD64_FULL |
                       MD_CONTEXT_AMD64_SEGMENTS;

  out->cs = info.regs.cs;

  out->ds = info.regs.ds;
  out->es = info.regs.es;
  out->fs = info.regs.fs;
  out->gs = info.regs.gs;

  out->ss = info.regs.ss;
  out->eflags = info.regs.eflags;

  out->dr0 = info.dregs[0];
  out->dr1 = info.dregs[1];
  out->dr2 = info.dregs[2];
  out->dr3 = info.dregs[3];
  // 4 and 5 deliberatly omitted because they aren't included in the minidump
  // format.
  out->dr6 = info.dregs[6];
  out->dr7 = info.dregs[7];

  out->rax = info.regs.rax;
  out->rcx = info.regs.rcx;
  out->rdx = info.regs.rdx;
  out->rbx = info.regs.rbx;

  out->rsp = info.regs.rsp;

  out->rbp = info.regs.rbp;
  out->rsi = info.regs.rsi;
  out->rdi = info.regs.rdi;
  out->r8 = info.regs.r8;
  out->r9 = info.regs.r9;
  out->r10 = info.regs.r10;
  out->r11 = info.regs.r11;
  out->r12 = info.regs.r12;
  out->r13 = info.regs.r13;
  out->r14 = info.regs.r14;
  out->r15 = info.regs.r15;

  out->rip = info.regs.rip;

  out->flt_save.control_word = info.fpregs.cwd;
  out->flt_save.status_word = info.fpregs.swd;
  out->flt_save.tag_word = info.fpregs.twd;
  out->flt_save.error_opcode = info.fpregs.fop;
  out->flt_save.error_offset = info.fpregs.rip;
  out->flt_save.error_selector = 0; // We don't have this.
  out->flt_save.data_offset = info.fpregs.rdp;
  out->flt_save.data_selector = 0;  // We don't have this.
  out->flt_save.mx_csr = info.fpregs.mxcsr;
  out->flt_save.mx_csr_mask = info.fpregs.mxcsr_mask;
  memcpy(&out->flt_save.float_registers, &info.fpregs.st_space, 8 * 16);
  memcpy(&out->flt_save.xmm_registers, &info.fpregs.xmm_space, 16 * 16);
}

static void CPUFillFromUContext(MDRawContextAMD64 *out, const ucontext *uc,
                                const struct _libc_fpstate* fpregs) {
  const greg_t* regs = uc->gregs;

  out->context_flags = MD_CONTEXT_AMD64_FULL;

  out->cs = regs[REG_CSGSFS] & 0xffff;

  out->fs = (regs[REG_CSGSFS] >> 32) & 0xffff;
  out->gs = (regs[REG_CSGSFS] >> 16) & 0xffff;

  out->eflags = regs[REG_EFL];

  out->rax = regs[REG_RAX];
  out->rcx = regs[REG_RCX];
  out->rdx = regs[REG_RDX];
  out->rbx = regs[REG_RBX];

  out->rsp = regs[REG_RSP];
  out->rbp = regs[REG_RBP];
  out->rsi = regs[REG_RSI];
  out->rdi = regs[REG_RDI];
  out->r8 = regs[REG_R8];
  out->r9 = regs[REG_R9];
  out->r10 = regs[REG_R10];
  out->r11 = regs[REG_R11];
  out->r12 = regs[REG_R12];
  out->r13 = regs[REG_R13];
  out->r14 = regs[REG_R14];
  out->r15 = regs[REG_R15];

  out->rip = regs[REG_RIP];

  out->flt_save.control_word = fpregs->cwd;
  out->flt_save.status_word = fpregs->swd;
  out->flt_save.tag_word = fpregs->ftw;
  out->flt_save.error_opcode = fpregs->fop;
  out->flt_save.error_offset = fpregs->rip;
  out->flt_save.data_offset = fpregs->rdp;
  out->flt_save.error_selector = 0; // We don't have this.
  out->flt_save.data_selector = 0;  // We don't have this.
  out->flt_save.mx_csr = fpregs->mxcsr;
  out->flt_save.mx_csr_mask = fpregs->mxcsr_mask;
  memcpy(&out->flt_save.float_registers, &fpregs->_st, 8 * 16);
  memcpy(&out->flt_save.xmm_registers, &fpregs->_xmm, 16 * 16);
}

#else
#error "This code has not been ported to your platform yet."
#endif

namespace google_breakpad {

class MinidumpWriter {
 public:
  MinidumpWriter(const char* filename,
                 pid_t crashing_pid,
                 const ExceptionHandler::CrashContext* context)
      : filename_(filename),
        siginfo_(&context->siginfo),
        ucontext_(&context->context),
        float_state_(&context->float_state),
        crashing_tid_(context->tid),
        dumper_(crashing_pid) {
  }

  bool Init() {
    return dumper_.Init() && minidump_writer_.Open(filename_) &&
           dumper_.ThreadsSuspend();
  }

  ~MinidumpWriter() {
    minidump_writer_.Close();
    dumper_.ThreadsResume();
  }

  bool Dump() {
    // A minidump file contains a number of tagged streams. This is the number
    // of stream which we write.
    static const unsigned kNumWriters = 11;

    TypedMDRVA<MDRawHeader> header(&minidump_writer_);
    TypedMDRVA<MDRawDirectory> dir(&minidump_writer_);
    if (!header.Allocate())
      return false;
    if (!dir.AllocateArray(kNumWriters))
      return false;
    memset(header.get(), 0, sizeof(MDRawHeader));

    header.get()->signature = MD_HEADER_SIGNATURE;
    header.get()->version = MD_HEADER_VERSION;
    header.get()->time_date_stamp = time(NULL);
    header.get()->stream_count = kNumWriters;
    header.get()->stream_directory_rva = dir.position();

    unsigned dir_index = 0;
    MDRawDirectory dirent;

    if (!WriteThreadListStream(&dirent))
      return false;
    dir.CopyIndex(dir_index++, &dirent);

    if (!WriteMappings(&dirent))
      return false;
    dir.CopyIndex(dir_index++, &dirent);

    if (!WriteExceptionStream(&dirent))
      return false;
    dir.CopyIndex(dir_index++, &dirent);

    if (!WriteSystemInfoStream(&dirent))
      return false;
    dir.CopyIndex(dir_index++, &dirent);

    dirent.stream_type = MD_LINUX_CPU_INFO;
    if (!WriteFile(&dirent.location, "/proc/cpuinfo"))
      NullifyDirectoryEntry(&dirent);
    dir.CopyIndex(dir_index++, &dirent);

    dirent.stream_type = MD_LINUX_PROC_STATUS;
    if (!WriteProcFile(&dirent.location, crashing_tid_, "status"))
      NullifyDirectoryEntry(&dirent);
    dir.CopyIndex(dir_index++, &dirent);

    dirent.stream_type = MD_LINUX_LSB_RELEASE;
    if (!WriteFile(&dirent.location, "/etc/lsb-release"))
      NullifyDirectoryEntry(&dirent);
    dir.CopyIndex(dir_index++, &dirent);

    dirent.stream_type = MD_LINUX_CMD_LINE;
    if (!WriteProcFile(&dirent.location, crashing_tid_, "cmdline"))
      NullifyDirectoryEntry(&dirent);
    dir.CopyIndex(dir_index++, &dirent);

    dirent.stream_type = MD_LINUX_ENVIRON;
    if (!WriteProcFile(&dirent.location, crashing_tid_, "environ"))
      NullifyDirectoryEntry(&dirent);
    dir.CopyIndex(dir_index++, &dirent);

    dirent.stream_type = MD_LINUX_AUXV;
    if (!WriteProcFile(&dirent.location, crashing_tid_, "auxv"))
      NullifyDirectoryEntry(&dirent);
    dir.CopyIndex(dir_index++, &dirent);

    dirent.stream_type = MD_LINUX_AUXV;
    if (!WriteProcFile(&dirent.location, crashing_tid_, "maps"))
      NullifyDirectoryEntry(&dirent);
    dir.CopyIndex(dir_index++, &dirent);

    // If you add more directory entries, don't forget to update kNumWriters,
    // above.

    dumper_.ThreadsResume();
    return true;
  }

  // Write information about the threads.
  bool WriteThreadListStream(MDRawDirectory* dirent) {
    const unsigned num_threads = dumper_.threads().size();

    TypedMDRVA<uint32_t> list(&minidump_writer_);
    if (!list.AllocateObjectAndArray(num_threads, sizeof(MDRawThread)))
      return false;

    dirent->stream_type = MD_THREAD_LIST_STREAM;
    dirent->location = list.location();

    *list.get() = num_threads;

    for (unsigned i = 0; i < num_threads; ++i) {
      MDRawThread thread;
      my_memset(&thread, 0, sizeof(thread));
      thread.thread_id = dumper_.threads()[i];
      // We have a different source of information for the crashing thread. If
      // we used the actual state of the thread we would find it running in the
      // signal handler with the alternative stack, which would be deeply
      // unhelpful.
      if (thread.thread_id == crashing_tid_) {
        const void* stack;
        size_t stack_len;
        if (!dumper_.GetStackInfo(&stack, &stack_len, GetStackPointer()))
          return false;
        UntypedMDRVA memory(&minidump_writer_);
        if (!memory.Allocate(stack_len))
          return false;
        uint8_t* stack_copy = (uint8_t*) dumper_.allocator()->Alloc(stack_len);
        dumper_.CopyFromProcess(stack_copy, thread.thread_id, stack, stack_len);
        memory.Copy(stack_copy, stack_len);
        thread.stack.start_of_memory_range = (uintptr_t) (stack);
        thread.stack.memory = memory.location();
        TypedMDRVA<RawContextCPU> cpu(&minidump_writer_);
        if (!cpu.Allocate())
          return false;
        my_memset(cpu.get(), 0, sizeof(RawContextCPU));
        CPUFillFromUContext(cpu.get(), ucontext_, float_state_);
        thread.thread_context = cpu.location();
        crashing_thread_context_ = cpu.location();
      } else {
        ThreadInfo info;
        if (!dumper_.ThreadInfoGet(dumper_.threads()[i], &info))
          return false;
        UntypedMDRVA memory(&minidump_writer_);
        if (!memory.Allocate(info.stack_len))
          return false;
        uint8_t* stack_copy =
            (uint8_t*) dumper_.allocator()->Alloc(info.stack_len);
        dumper_.CopyFromProcess(stack_copy, thread.thread_id, info.stack,
                                info.stack_len);
        memory.Copy(stack_copy, info.stack_len);
        thread.stack.start_of_memory_range = (uintptr_t)(info.stack);
        thread.stack.memory = memory.location();
        TypedMDRVA<RawContextCPU> cpu(&minidump_writer_);
        if (!cpu.Allocate())
          return false;
        my_memset(cpu.get(), 0, sizeof(RawContextCPU));
        CPUFillFromThreadInfo(cpu.get(), info);
        thread.thread_context = cpu.location();
      }

      list.CopyIndexAfterObject(i, &thread, sizeof(thread));
    }

    return true;
  }

  static bool ShouldIncludeMapping(const MappingInfo& mapping) {
    if (mapping.name[0] == 0 || // we only want modules with filenames.
        mapping.offset || // we only want to include one mapping per shared lib.
        mapping.size < 4096) {  // too small to get a signature for.
      return false;
    }

    return true;
  }

  // Write information about the mappings in effect. Because we are using the
  // minidump format, the information about the mappings is pretty limited.
  // Because of this, we also include the full, unparsed, /proc/$x/maps file in
  // another stream in the file.
  bool WriteMappings(MDRawDirectory* dirent) {
    const unsigned num_mappings = dumper_.mappings().size();
    unsigned num_output_mappings = 0;

    for (unsigned i = 0; i < dumper_.mappings().size(); ++i) {
      const MappingInfo& mapping = *dumper_.mappings()[i];
      if (ShouldIncludeMapping(mapping))
        num_output_mappings++;
    }

    TypedMDRVA<uint32_t> list(&minidump_writer_);
    if (!list.AllocateObjectAndArray(num_output_mappings, sizeof(MDRawModule)))
      return false;

    dirent->stream_type = MD_MODULE_LIST_STREAM;
    dirent->location = list.location();
    *list.get() = num_output_mappings;

    for (unsigned i = 0, j = 0; i < num_mappings; ++i) {
      const MappingInfo& mapping = *dumper_.mappings()[i];
      if (!ShouldIncludeMapping(mapping))
        continue;

      MDRawModule mod;
      my_memset(&mod, 0, sizeof(mod));
      mod.base_of_image = mapping.start_addr;
      mod.size_of_image = mapping.size;
      const size_t filepath_len = my_strlen(mapping.name);

      // Figure out file name from path
      const char* filename_ptr = mapping.name + filepath_len - 1;
      while (filename_ptr >= mapping.name) {
        if (*filename_ptr == '/')
          break;
        filename_ptr--;
      }
      filename_ptr++;
      const size_t filename_len = mapping.name + filepath_len - filename_ptr;

      uint8_t cv_buf[MDCVInfoPDB70_minsize + NAME_MAX];
      uint8_t* cv_ptr = cv_buf;
      UntypedMDRVA cv(&minidump_writer_);
      if (!cv.Allocate(MDCVInfoPDB70_minsize + filename_len + 1))
        return false;

      const uint32_t cv_signature = MD_CVINFOPDB70_SIGNATURE;
      memcpy(cv_ptr, &cv_signature, sizeof(cv_signature));
      cv_ptr += sizeof(cv_signature);

      {
        // We XOR the first page of the file to get a signature for it.
        uint8_t xor_buf[sizeof(MDGUID)];
        size_t done = 0;
        uint8_t* signature = cv_ptr;
        cv_ptr += sizeof(xor_buf);

        my_memset(signature, 0, sizeof(xor_buf));
        while (done < 4096) {
          dumper_.CopyFromProcess(xor_buf, crashing_tid_,
                                  (void *) (mod.base_of_image + done),
                                  sizeof(xor_buf));
          for (unsigned i = 0; i < sizeof(xor_buf); ++i)
            signature[i] ^= xor_buf[i];
          done += sizeof(xor_buf);
        }
        cv_ptr += sizeof(uint32_t);  // Skip age field
      }

      // Write pdb_file_name
      memcpy(cv_ptr, filename_ptr, filename_len + 1);
      cv.Copy(cv_buf, MDCVInfoPDB70_minsize + filename_len + 1);

      mod.cv_record = cv.location();

      MDLocationDescriptor ld;
      if (!minidump_writer_.WriteString(mapping.name, filepath_len, &ld))
        return false;
      mod.module_name_rva = ld.rva;

      list.CopyIndexAfterObject(j++, &mod, sizeof(mod));
    }

    return true;
  }

  bool WriteExceptionStream(MDRawDirectory* dirent) {
    TypedMDRVA<MDRawExceptionStream> exc(&minidump_writer_);
    if (!exc.Allocate())
      return false;
    my_memset(exc.get(), 0, sizeof(MDRawExceptionStream));

    dirent->stream_type = MD_EXCEPTION_STREAM;
    dirent->location = exc.location();

    exc.get()->thread_id = crashing_tid_;
    exc.get()->exception_record.exception_code = siginfo_->si_signo;
    exc.get()->exception_record.exception_address =
        (uintptr_t) siginfo_->si_addr;
    exc.get()->thread_context = crashing_thread_context_;

    return true;
  }

  bool WriteSystemInfoStream(MDRawDirectory* dirent) {
    TypedMDRVA<MDRawSystemInfo> si(&minidump_writer_);
    if (!si.Allocate())
      return false;
    my_memset(si.get(), 0, sizeof(MDRawSystemInfo));

    dirent->stream_type = MD_SYSTEM_INFO_STREAM;
    dirent->location = si.location();

    WriteCPUInformation(si.get());

    return true;
  }

 private:
#if defined(__i386)
  uintptr_t GetStackPointer() {
    return ucontext_->uc_mcontext.gregs[REG_ESP];
  }
#elif defined(__x86_64)
  uintptr_t GetStackPointer() {
    return ucontext_->uc_mcontext.gregs[REG_RSP];
  }
#else
#error "This code has not been ported to your platform yet."
#endif

  void NullifyDirectoryEntry(MDRawDirectory* dirent) {
    dirent->stream_type = 0;
    dirent->location.data_size = 0;
    dirent->location.rva = 0;
  }

  bool WriteCPUInformation(MDRawSystemInfo* sys_info) {
    char vendor_id[sizeof(sys_info->cpu.x86_cpu_info.vendor_id) + 1] = {0};
    static const char vendor_id_name[] = "vendor_id";
    static const size_t vendor_id_name_length = sizeof(vendor_id_name) - 1;

    struct CpuInfoEntry {
      const char* info_name;
      int value;
      bool found;
    } cpu_info_table[] = {
      { "processor", -1, false },
      { "model", 0, false },
      { "stepping",  0, false },
      { "cpuid level", 0, false },
    };

    // processor_architecture should always be set, do this first
    sys_info->processor_architecture =
#if defined(__i386)
        MD_CPU_ARCHITECTURE_X86;
#elif defined(__x86_64)
        MD_CPU_ARCHITECTURE_AMD64;
#else
#error "Unknown CPU arch"
#endif

    static const char proc_cpu_path[] = "/proc/cpuinfo";
    FILE* fp = fopen(proc_cpu_path, "r");
    if (!fp)
      return false;

    {
      char line[128];
      while (fgets(line, sizeof(line), fp)) {
        for (size_t i = 0;
             i < sizeof(cpu_info_table) / sizeof(cpu_info_table[0]);
             i++) {
          CpuInfoEntry* entry = &cpu_info_table[i];
          if (entry->found)
            continue;
          if (!strncmp(line, entry->info_name, strlen(entry->info_name))) {
            char* value = strchr(line, ':');
            if (!value)
              continue;

            // the above strncmp only matches the prefix, it might be the wrong
            // line. i.e. we matched "model name" instead of "model".
            // check and make sure there is only spaces between the prefix and
            // the colon.
            char* space_ptr = line + strlen(entry->info_name);
            for (; space_ptr < value; space_ptr++) {
              if (!isspace(*space_ptr)) {
                break;
              }
            }
            if (space_ptr != value)
              continue;

            sscanf(++value, " %d", &(entry->value));
            entry->found = true;
          }
        }

        // special case for vendor_id
        if (!strncmp(line, vendor_id_name, vendor_id_name_length)) {
          char* value = strchr(line, ':');
          if (!value)
            continue;

          // skip ':" and all the spaces that follows
          do {
            value++;
          } while (isspace(*value));

          if (*value) {
            size_t length = strlen(value);
            if (length == 0)
              continue;
            // we don't want the trailing newline
            if (value[length - 1] == '\n')
              length--;
            // ensure we have space for the value
            if (length < sizeof(vendor_id))
              strncpy(vendor_id, value, length);
          }
        }
      }
      fclose(fp);
    }

    // make sure we got everything we wanted
    for (size_t i = 0;
         i < sizeof(cpu_info_table) / sizeof(cpu_info_table[0]);
         i++) {
      if (!cpu_info_table[i].found) {
        return false;
      }
    }
    // /proc/cpuinfo contains cpu id, change it into number by adding one.
    cpu_info_table[0].value++;

    sys_info->number_of_processors = cpu_info_table[0].value;
    sys_info->processor_level      = cpu_info_table[3].value;
    sys_info->processor_revision   = cpu_info_table[1].value << 8 |
                                     cpu_info_table[2].value;

    if (vendor_id[0] != '\0') {
      memcpy(sys_info->cpu.x86_cpu_info.vendor_id, vendor_id,
             sizeof(sys_info->cpu.x86_cpu_info.vendor_id));
    }
    return true;
  }

  bool WriteFile(MDLocationDescriptor* result, const char* filename) {
    const int fd = sys_open(filename, O_RDONLY, 0);
    if (fd < 0)
      return false;

    // We can't stat the files because several of the files that we want to
    // read are kernel seqfiles, which always have a length of zero. So we have
    // to read as much as we can into a buffer.
    static const unsigned kMaxFileSize = 1024;
    uint8_t* data = (uint8_t*) dumper_.allocator()->Alloc(kMaxFileSize);

    size_t done = 0;
    while (done < kMaxFileSize) {
      ssize_t r;
      do {
        r = sys_read(fd, data + done, kMaxFileSize - done);
      } while (r == -1 && errno == EINTR);

      if (r < 1)
        break;
      done += r;
    }
    sys_close(fd);

    if (!done)
      return false;

    UntypedMDRVA memory(&minidump_writer_);
    if (!memory.Allocate(done))
      return false;
    memory.Copy(data, done);
    *result = memory.location();
    return true;
  }

  bool WriteProcFile(MDLocationDescriptor* result, pid_t pid,
                     const char* filename) {
    char buf[80];
    memcpy(buf, "/proc/", 6);
    const unsigned pid_len = my_int_len(pid);
    my_itos(buf + 6, pid, pid_len);
    buf[6 + pid_len] = '/';
    memcpy(buf + 6 + pid_len + 1, filename, my_strlen(filename) + 1);
    return WriteFile(result, buf);
  }

  const char* const filename_;  // output filename
  const siginfo_t* const siginfo_;  // from the signal handler (see sigaction)
  const struct ucontext* const ucontext_;  // also from the signal handler
  const struct _libc_fpstate* const float_state_;  // ditto
  const pid_t crashing_tid_;  // the process which actually crashed
  LinuxDumper dumper_;
  MinidumpFileWriter minidump_writer_;
  MDLocationDescriptor crashing_thread_context_;
};

bool WriteMinidump(const char* filename, pid_t crashing_process,
                   const void* blob, size_t blob_size) {
  if (blob_size != sizeof(ExceptionHandler::CrashContext))
    return false;
  const ExceptionHandler::CrashContext* context =
      reinterpret_cast<const ExceptionHandler::CrashContext*>(blob);
  MinidumpWriter writer(filename, crashing_process, context);
  if (!writer.Init())
    return false;
  return writer.Dump();
}

}  // namespace google_breakpad