Linux: Add Breakpad client.

breakpad/linux/minidump_writer.cc

Index: breakpad/linux/minidump_writer.cc
diff --git a/breakpad/linux/minidump_writer.cc b/breakpad/linux/minidump_writer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..5a1d6c64914dc11c896e24c06c533e0a1e42bf5b
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+++ b/breakpad/linux/minidump_writer.cc
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+// 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 greg_t* regs = uc->uc_mcontext.gregs;
+  const fpregset_t fp = uc->uc_mcontext.fpregs;
+
+  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 greg_t* regs = uc->gregs;
+  const fpregset_t fpregs = uc->fpregs;
+
+  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),
+        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 = 10;
+
+    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);
+
+    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_);
+        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;
+  }
+
+  // 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();
+
+    TypedMDRVA<uint32_t> list(&minidump_writer_);
+    if (!list.AllocateObjectAndArray(num_mappings, sizeof(MDRawModule)))
+      return false;
+
+    dirent->stream_type = MD_MODULE_LIST_STREAM;
+    dirent->location = list.location();
+    *list.get() = num_mappings;
+
+    for (unsigned i = 0; i < num_mappings; ++i) {
+      const MappingInfo& mapping = *dumper_.mappings()[i];
+      MDRawModule mod;
+      my_memset(&mod, 0, sizeof(mod));
+      mod.base_of_image = mapping.start_addr;
+      mod.size_of_image = mapping.size;
+      UntypedMDRVA memory(&minidump_writer_);
+      const size_t filename_len = my_strlen(mapping.name);
+
+      if (filename_len) {
+        MDLocationDescriptor ld;
+        if (!minidump_writer_.WriteString(mapping.name, filename_len, &ld))
+          return false;
+        mod.module_name_rva = ld.rva;
+      }
+
+      list.CopyIndexAfterObject(i, &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;
+  }
+
+ 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 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 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