Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 875 insertions, 0 deletions

diff --git a/toolkit/crashreporter/breakpad-client/linux/handler/exception_handler.cc b/toolkit/crashreporter/breakpad-client/linux/handler/exception_handler.cc
new file mode 100644
index 0000000000..ab17661ad7
--- /dev/null
+++ b/toolkit/crashreporter/breakpad-client/linux/handler/exception_handler.cc
@@ -0,0 +1,875 @@
+// Copyright (c) 2010 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.
+
+// The ExceptionHandler object installs signal handlers for a number of
+// signals. We rely on the signal handler running on the thread which crashed
+// in order to identify it. This is true of the synchronous signals (SEGV etc),
+// but not true of ABRT. Thus, if you send ABRT to yourself in a program which
+// uses ExceptionHandler, you need to use tgkill to direct it to the current
+// thread.
+//
+// The signal flow looks like this:
+//
+//   SignalHandler (uses a global stack of ExceptionHandler objects to find
+//        |         one to handle the signal. If the first rejects it, try
+//        |         the second etc...)
+//        V
+//   HandleSignal ----------------------------| (clones a new process which
+//        |                                   |  shares an address space with
+//   (wait for cloned                         |  the crashed process. This
+//     process)                               |  allows us to ptrace the crashed
+//        |                                   |  process)
+//        V                                   V
+//   (set signal handler to             ThreadEntry (static function to bounce
+//    SIG_DFL and rethrow,                    |      back into the object)
+//    killing the crashed                     |
+//    process)                                V
+//                                          DoDump  (writes minidump)
+//                                            |
+//                                            V
+//                                         sys_exit
+//
+
+// This code is a little fragmented. Different functions of the ExceptionHandler
+// class run in a number of different contexts. Some of them run in a normal
+// context and are easy to code, others run in a compromised context and the
+// restrictions at the top of minidump_writer.cc apply: no libc and use the
+// alternative malloc. Each function should have comment above it detailing the
+// context which it runs in.
+
+#include "linux/handler/exception_handler.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/limits.h>
+#include <pthread.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <sys/mman.h>
+#include <sys/prctl.h>
+#include <sys/syscall.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <sys/ucontext.h>
+#include <sys/user.h>
+#include <ucontext.h>
+
+#include <algorithm>
+#include <utility>
+#include <vector>
+
+#include "common/basictypes.h"
+#include "common/linux/breakpad_getcontext.h"
+#include "common/linux/linux_libc_support.h"
+#include "common/memory_allocator.h"
+#include "linux/log/log.h"
+#include "linux/microdump_writer/microdump_writer.h"
+#include "linux/minidump_writer/linux_dumper.h"
+#include "linux/minidump_writer/minidump_writer.h"
+#include "common/linux/eintr_wrapper.h"
+#include "third_party/lss/linux_syscall_support.h"
+#if defined(MOZ_OXIDIZED_BREAKPAD)
+#include "nsString.h"
+#include "mozilla/toolkit/crashreporter/rust_minidump_writer_linux_ffi_generated.h"
+#endif
+
+#ifdef MOZ_PHC
+#include "replace_malloc_bridge.h"
+#endif
+
+#if defined(__ANDROID__)
+#include "linux/sched.h"
+#endif
+
+#ifndef PR_SET_PTRACER
+#define PR_SET_PTRACER 0x59616d61
+#endif
+
+#define SKIP_SIGILL(sig) if (g_skip_sigill_ && (sig == SIGILL)) continue;
+
+namespace google_breakpad {
+
+namespace {
+// The list of signals which we consider to be crashes. The default action for
+// all these signals must be Core (see man 7 signal) because we rethrow the
+// signal after handling it and expect that it'll be fatal.
+const int kExceptionSignals[] = {
+  SIGSEGV, SIGABRT, SIGFPE, SIGILL, SIGBUS, SIGTRAP
+};
+const int kNumHandledSignals =
+    sizeof(kExceptionSignals) / sizeof(kExceptionSignals[0]);
+struct sigaction old_handlers[kNumHandledSignals];
+bool handlers_installed = false;
+
+// InstallAlternateStackLocked will store the newly installed stack in new_stack
+// and (if it exists) the previously installed stack in old_stack.
+stack_t old_stack;
+stack_t new_stack;
+bool stack_installed = false;
+
+// Create an alternative stack to run the signal handlers on. This is done since
+// the signal might have been caused by a stack overflow.
+// Runs before crashing: normal context.
+void InstallAlternateStackLocked() {
+  if (stack_installed)
+    return;
+
+  memset(&old_stack, 0, sizeof(old_stack));
+  memset(&new_stack, 0, sizeof(new_stack));
+
+  // SIGSTKSZ may be too small to prevent the signal handlers from overrunning
+  // the alternative stack. Ensure that the size of the alternative stack is
+  // large enough.
+  static const size_t kSigStackSize = std::max(size_t(16384), size_t(SIGSTKSZ));
+
+  // Only set an alternative stack if there isn't already one, or if the current
+  // one is too small.
+  if (sys_sigaltstack(NULL, &old_stack) == -1 || !old_stack.ss_sp ||
+      old_stack.ss_size < kSigStackSize) {
+    new_stack.ss_sp = calloc(1, kSigStackSize);
+    new_stack.ss_size = kSigStackSize;
+
+    if (sys_sigaltstack(&new_stack, NULL) == -1) {
+      free(new_stack.ss_sp);
+      return;
+    }
+    stack_installed = true;
+  }
+}
+
+// Runs before crashing: normal context.
+void RestoreAlternateStackLocked() {
+  if (!stack_installed)
+    return;
+
+  stack_t current_stack;
+  if (sys_sigaltstack(NULL, &current_stack) == -1)
+    return;
+
+  // Only restore the old_stack if the current alternative stack is the one
+  // installed by the call to InstallAlternateStackLocked.
+  if (current_stack.ss_sp == new_stack.ss_sp) {
+    if (old_stack.ss_sp) {
+      if (sys_sigaltstack(&old_stack, NULL) == -1)
+        return;
+    } else {
+      stack_t disable_stack;
+      disable_stack.ss_flags = SS_DISABLE;
+      if (sys_sigaltstack(&disable_stack, NULL) == -1)
+        return;
+    }
+  }
+
+  free(new_stack.ss_sp);
+  stack_installed = false;
+}
+
+void InstallDefaultHandler(int sig) {
+#if defined(__ANDROID__)
+  // Android L+ expose signal and sigaction symbols that override the system
+  // ones. There is a bug in these functions where a request to set the handler
+  // to SIG_DFL is ignored. In that case, an infinite loop is entered as the
+  // signal is repeatedly sent to breakpad's signal handler.
+  // To work around this, directly call the system's sigaction.
+  struct kernel_sigaction sa;
+  memset(&sa, 0, sizeof(sa));
+  sys_sigemptyset(&sa.sa_mask);
+  sa.sa_handler_ = SIG_DFL;
+  sa.sa_flags = SA_RESTART;
+  sys_rt_sigaction(sig, &sa, NULL, sizeof(kernel_sigset_t));
+#else
+  signal(sig, SIG_DFL);
+#endif
+}
+
+// The global exception handler stack. This is needed because there may exist
+// multiple ExceptionHandler instances in a process. Each will have itself
+// registered in this stack.
+std::vector<ExceptionHandler*>* g_handler_stack_ = NULL;
+pthread_mutex_t g_handler_stack_mutex_ = PTHREAD_MUTEX_INITIALIZER;
+
+// sizeof(CrashContext) can be too big w.r.t the size of alternatate stack
+// for SignalHandler(). Keep the crash context as a .bss field. Exception
+// handlers are serialized by the |g_handler_stack_mutex_| and at most one at a
+// time can use |g_crash_context_|.
+ExceptionHandler::CrashContext g_crash_context_;
+
+FirstChanceHandler g_first_chance_handler_ = nullptr;
+bool g_skip_sigill_ = false;
+}  // namespace
+
+// Runs before crashing: normal context.
+ExceptionHandler::ExceptionHandler(const MinidumpDescriptor& descriptor,
+                                   FilterCallback filter,
+                                   MinidumpCallback callback,
+                                   void* callback_context,
+                                   bool install_handler,
+                                   const int server_fd)
+    : filter_(filter),
+      callback_(callback),
+      callback_context_(callback_context),
+      minidump_descriptor_(descriptor),
+      crash_handler_(NULL) {
+
+  g_skip_sigill_ = getenv("MOZ_DISABLE_EXCEPTION_HANDLER_SIGILL") ? true : false;
+  if (server_fd >= 0)
+    crash_generation_client_.reset(CrashGenerationClient::TryCreate(server_fd));
+
+  if (!IsOutOfProcess() && !minidump_descriptor_.IsFD() &&
+      !minidump_descriptor_.IsMicrodumpOnConsole())
+    minidump_descriptor_.UpdatePath();
+
+#if defined(__ANDROID__)
+  if (minidump_descriptor_.IsMicrodumpOnConsole())
+    logger::initializeCrashLogWriter();
+#endif
+
+  pthread_mutex_lock(&g_handler_stack_mutex_);
+
+  // Pre-fault the crash context struct. This is to avoid failing due to OOM
+  // if handling an exception when the process ran out of virtual memory.
+  memset(&g_crash_context_, 0, sizeof(g_crash_context_));
+
+  if (!g_handler_stack_)
+    g_handler_stack_ = new std::vector<ExceptionHandler*>;
+  if (install_handler) {
+    InstallAlternateStackLocked();
+    InstallHandlersLocked();
+  }
+  g_handler_stack_->push_back(this);
+  pthread_mutex_unlock(&g_handler_stack_mutex_);
+}
+
+// Runs before crashing: normal context.
+ExceptionHandler::~ExceptionHandler() {
+  pthread_mutex_lock(&g_handler_stack_mutex_);
+  std::vector<ExceptionHandler*>::iterator handler =
+      std::find(g_handler_stack_->begin(), g_handler_stack_->end(), this);
+  g_handler_stack_->erase(handler);
+  if (g_handler_stack_->empty()) {
+    delete g_handler_stack_;
+    g_handler_stack_ = NULL;
+    RestoreAlternateStackLocked();
+    RestoreHandlersLocked();
+  }
+  pthread_mutex_unlock(&g_handler_stack_mutex_);
+}
+
+// Runs before crashing: normal context.
+// static
+bool ExceptionHandler::InstallHandlersLocked() {
+  if (handlers_installed)
+    return false;
+
+  // Fail if unable to store all the old handlers.
+  for (int i = 0; i < kNumHandledSignals; ++i) {
+    SKIP_SIGILL(kExceptionSignals[i]);
+    if (sigaction(kExceptionSignals[i], NULL, &old_handlers[i]) == -1)
+      return false;
+  }
+
+  struct sigaction sa;
+  memset(&sa, 0, sizeof(sa));
+  sigemptyset(&sa.sa_mask);
+
+  // Mask all exception signals when we're handling one of them.
+  for (int i = 0; i < kNumHandledSignals; ++i) {
+    SKIP_SIGILL(kExceptionSignals[i]);
+    sigaddset(&sa.sa_mask, kExceptionSignals[i]);
+  }
+
+  sa.sa_sigaction = SignalHandler;
+  sa.sa_flags = SA_ONSTACK | SA_SIGINFO;
+
+  for (int i = 0; i < kNumHandledSignals; ++i) {
+    SKIP_SIGILL(kExceptionSignals[i]);
+    if (sigaction(kExceptionSignals[i], &sa, NULL) == -1) {
+      // At this point it is impractical to back out changes, and so failure to
+      // install a signal is intentionally ignored.
+    }
+  }
+  handlers_installed = true;
+  return true;
+}
+
+// This function runs in a compromised context: see the top of the file.
+// Runs on the crashing thread.
+// static
+void ExceptionHandler::RestoreHandlersLocked() {
+  if (!handlers_installed)
+    return;
+
+  for (int i = 0; i < kNumHandledSignals; ++i) {
+    SKIP_SIGILL(kExceptionSignals[i]);
+    if (sigaction(kExceptionSignals[i], &old_handlers[i], NULL) == -1) {
+      InstallDefaultHandler(kExceptionSignals[i]);
+    }
+  }
+  handlers_installed = false;
+}
+
+// void ExceptionHandler::set_crash_handler(HandlerCallback callback) {
+//   crash_handler_ = callback;
+// }
+
+// This function runs in a compromised context: see the top of the file.
+// Runs on the crashing thread.
+// static
+void ExceptionHandler::SignalHandler(int sig, siginfo_t* info, void* uc) {
+
+  // Give the first chance handler a chance to recover from this signal
+  //
+  // This is primarily used by V8. V8 uses guard regions to guarantee memory
+  // safety in WebAssembly. This means some signals might be expected if they
+  // originate from Wasm code while accessing the guard region. We give V8 the
+  // chance to handle and recover from these signals first.
+  if (g_first_chance_handler_ != nullptr &&
+      g_first_chance_handler_(sig, info, uc)) {
+    return;
+  }
+
+  // All the exception signals are blocked at this point.
+  pthread_mutex_lock(&g_handler_stack_mutex_);
+
+  // Sometimes, Breakpad runs inside a process where some other buggy code
+  // saves and restores signal handlers temporarily with 'signal'
+  // instead of 'sigaction'. This loses the SA_SIGINFO flag associated
+  // with this function. As a consequence, the values of 'info' and 'uc'
+  // become totally bogus, generally inducing a crash.
+  //
+  // The following code tries to detect this case. When it does, it
+  // resets the signal handlers with sigaction + SA_SIGINFO and returns.
+  // This forces the signal to be thrown again, but this time the kernel
+  // will call the function with the right arguments.
+  struct sigaction cur_handler;
+  if (sigaction(sig, NULL, &cur_handler) == 0 &&
+      cur_handler.sa_sigaction == SignalHandler &&
+      (cur_handler.sa_flags & SA_SIGINFO) == 0) {
+    // Reset signal handler with the right flags.
+    sigemptyset(&cur_handler.sa_mask);
+    sigaddset(&cur_handler.sa_mask, sig);
+
+    cur_handler.sa_sigaction = SignalHandler;
+    cur_handler.sa_flags = SA_ONSTACK | SA_SIGINFO;
+
+    if (sigaction(sig, &cur_handler, NULL) == -1) {
+      // When resetting the handler fails, try to reset the
+      // default one to avoid an infinite loop here.
+      InstallDefaultHandler(sig);
+    }
+    pthread_mutex_unlock(&g_handler_stack_mutex_);
+    return;
+  }
+
+  bool handled = false;
+  for (int i = g_handler_stack_->size() - 1; !handled && i >= 0; --i) {
+    handled = (*g_handler_stack_)[i]->HandleSignal(sig, info, uc);
+  }
+
+  // Upon returning from this signal handler, sig will become unmasked and then
+  // it will be retriggered. If one of the ExceptionHandlers handled it
+  // successfully, restore the default handler. Otherwise, restore the
+  // previously installed handler. Then, when the signal is retriggered, it will
+  // be delivered to the appropriate handler.
+  if (handled) {
+    InstallDefaultHandler(sig);
+  } else {
+    RestoreHandlersLocked();
+  }
+
+  pthread_mutex_unlock(&g_handler_stack_mutex_);
+
+  // info->si_code <= 0 iff SI_FROMUSER (SI_FROMKERNEL otherwise).
+  if (info->si_code <= 0 || sig == SIGABRT) {
+    // This signal was triggered by somebody sending us the signal with kill().
+    // In order to retrigger it, we have to queue a new signal by calling
+    // kill() ourselves.  The special case (si_pid == 0 && sig == SIGABRT) is
+    // due to the kernel sending a SIGABRT from a user request via SysRQ.
+    if (sys_tgkill(getpid(), syscall(__NR_gettid), sig) < 0) {
+      // If we failed to kill ourselves (e.g. because a sandbox disallows us
+      // to do so), we instead resort to terminating our process. This will
+      // result in an incorrect exit code.
+      _exit(1);
+    }
+  } else {
+    // This was a synchronous signal triggered by a hard fault (e.g. SIGSEGV).
+    // No need to reissue the signal. It will automatically trigger again,
+    // when we return from the signal handler.
+  }
+}
+
+struct ThreadArgument {
+  pid_t pid;  // the crashing process
+  const MinidumpDescriptor* minidump_descriptor;
+  ExceptionHandler* handler;
+  const void* context;  // a CrashContext structure
+  size_t context_size;
+};
+
+// This is the entry function for the cloned process. We are in a compromised
+// context here: see the top of the file.
+// static
+int ExceptionHandler::ThreadEntry(void *arg) {
+  const ThreadArgument *thread_arg = reinterpret_cast<ThreadArgument*>(arg);
+
+  // Close the write end of the pipe. This allows us to fail if the parent dies
+  // while waiting for the continue signal.
+  sys_close(thread_arg->handler->fdes[1]);
+
+  // Block here until the crashing process unblocks us when
+  // we're allowed to use ptrace
+  thread_arg->handler->WaitForContinueSignal();
+  sys_close(thread_arg->handler->fdes[0]);
+
+  return thread_arg->handler->DoDump(thread_arg->pid, thread_arg->context,
+                                     thread_arg->context_size) == false;
+}
+
+#ifdef MOZ_PHC
+static void GetPHCAddrInfo(siginfo_t* siginfo,
+                           mozilla::phc::AddrInfo* addr_info) {
+  // Is this a crash involving a PHC allocation?
+  if (siginfo->si_signo == SIGSEGV || siginfo->si_signo == SIGBUS) {
+    ReplaceMalloc::IsPHCAllocation(siginfo->si_addr, addr_info);
+  }
+}
+#endif
+
+// This function runs in a compromised context: see the top of the file.
+// Runs on the crashing thread.
+bool ExceptionHandler::HandleSignal(int /*sig*/, siginfo_t* info, void* uc) {
+  mozilla::phc::AddrInfo addr_info;
+#ifdef MOZ_PHC
+  GetPHCAddrInfo(info, &addr_info);
+#endif
+
+  if (filter_ && !filter_(callback_context_))
+    return false;
+
+  // Allow ourselves to be dumped if the signal is trusted.
+  bool signal_trusted = info->si_code > 0;
+  bool signal_pid_trusted = info->si_code == SI_USER ||
+      info->si_code == SI_TKILL;
+  if (signal_trusted || (signal_pid_trusted && info->si_pid == getpid())) {
+    sys_prctl(PR_SET_DUMPABLE, 1, 0, 0, 0);
+  }
+
+  // Fill in all the holes in the struct to make Valgrind happy.
+  memset(&g_crash_context_, 0, sizeof(g_crash_context_));
+  memcpy(&g_crash_context_.siginfo, info, sizeof(siginfo_t));
+  memcpy(&g_crash_context_.context, uc, sizeof(ucontext_t));
+#if defined(__aarch64__)
+  ucontext_t* uc_ptr = (ucontext_t*)uc;
+  struct fpsimd_context* fp_ptr =
+      (struct fpsimd_context*)&uc_ptr->uc_mcontext.__reserved;
+  if (fp_ptr->head.magic == FPSIMD_MAGIC) {
+    memcpy(&g_crash_context_.float_state, fp_ptr,
+           sizeof(g_crash_context_.float_state));
+  }
+#elif !defined(__ARM_EABI__) && !defined(__mips__)
+  // FP state is not part of user ABI on ARM Linux.
+  // In case of MIPS Linux FP state is already part of ucontext_t
+  // and 'float_state' is not a member of CrashContext.
+  ucontext_t* uc_ptr = (ucontext_t*)uc;
+  if (uc_ptr->uc_mcontext.fpregs) {
+    memcpy(&g_crash_context_.float_state, uc_ptr->uc_mcontext.fpregs,
+           sizeof(g_crash_context_.float_state));
+  }
+#endif
+  g_crash_context_.tid = syscall(__NR_gettid);
+  if (crash_handler_ != NULL) {
+    if (crash_handler_(&g_crash_context_, sizeof(g_crash_context_),
+                       callback_context_)) {
+      return true;
+    }
+  }
+
+  return GenerateDump(&g_crash_context_, &addr_info);
+}
+
+// This is a public interface to HandleSignal that allows the client to
+// generate a crash dump. This function may run in a compromised context.
+bool ExceptionHandler::SimulateSignalDelivery(int sig) {
+  siginfo_t siginfo = {};
+  // Mimic a trusted signal to allow tracing the process (see
+  // ExceptionHandler::HandleSignal().
+  siginfo.si_code = SI_USER;
+  siginfo.si_pid = getpid();
+  ucontext_t context;
+  getcontext(&context);
+  return HandleSignal(sig, &siginfo, &context);
+}
+
+// This function may run in a compromised context: see the top of the file.
+bool ExceptionHandler::GenerateDump(
+    CrashContext *context, const mozilla::phc::AddrInfo* addr_info) {
+  if (IsOutOfProcess()) {
+    bool success =
+      crash_generation_client_->RequestDump(context, sizeof(*context));
+
+    if (callback_) {
+      success =
+        callback_(minidump_descriptor_, callback_context_, addr_info, success);
+    }
+
+    return success;
+  }
+
+  // Allocating too much stack isn't a problem, and better to err on the side
+  // of caution than smash it into random locations.
+  static const unsigned kChildStackSize = 16000;
+  PageAllocator allocator;
+  uint8_t* stack = reinterpret_cast<uint8_t*>(allocator.Alloc(kChildStackSize));
+  if (!stack)
+    return false;
+  // clone() needs the top-most address. (scrub just to be safe)
+  stack += kChildStackSize;
+  my_memset(stack - 16, 0, 16);
+
+  ThreadArgument thread_arg;
+  thread_arg.handler = this;
+  thread_arg.minidump_descriptor = &minidump_descriptor_;
+  thread_arg.pid = getpid();
+  thread_arg.context = context;
+  thread_arg.context_size = sizeof(*context);
+
+  // We need to explicitly enable ptrace of parent processes on some
+  // kernels, but we need to know the PID of the cloned process before we
+  // can do this. Create a pipe here which we can use to block the
+  // cloned process after creating it, until we have explicitly enabled ptrace
+  if (sys_pipe(fdes) == -1) {
+    // Creating the pipe failed. We'll log an error but carry on anyway,
+    // as we'll probably still get a useful crash report. All that will happen
+    // is the write() and read() calls will fail with EBADF
+    static const char no_pipe_msg[] = "ExceptionHandler::GenerateDump "
+                                      "sys_pipe failed:";
+    logger::write(no_pipe_msg, sizeof(no_pipe_msg) - 1);
+    logger::write(strerror(errno), strlen(strerror(errno)));
+    logger::write("\n", 1);
+
+    // Ensure fdes[0] and fdes[1] are invalid file descriptors.
+    fdes[0] = fdes[1] = -1;
+  }
+
+  const pid_t child = sys_clone(
+      ThreadEntry, stack, CLONE_FS | CLONE_UNTRACED, &thread_arg, NULL, NULL,
+      NULL);
+  if (child == -1) {
+    sys_close(fdes[0]);
+    sys_close(fdes[1]);
+    return false;
+  }
+
+  if (child != 0) {
+    static const char clonedMsg[] =
+      "ExceptionHandler::GenerateDump cloned child ";
+    char pidMsg[32] = {};
+
+    unsigned int pidLen = my_uint_len(child);
+    my_uitos(pidMsg, child, pidLen);
+
+    logger::write(clonedMsg, my_strlen(clonedMsg));
+    logger::write(pidMsg, pidLen);
+    logger::write("\n", 1);
+  } else {
+    static const char childMsg[] =
+      "ExceptionHandler::GenerateDump I'm the child\n";
+    logger::write(childMsg, my_strlen(childMsg));
+  }
+
+  // Close the read end of the pipe.
+  sys_close(fdes[0]);
+  // Allow the child to ptrace us
+  sys_prctl(PR_SET_PTRACER, child, 0, 0, 0);
+  SendContinueSignalToChild();
+  int status = 0;
+  const int r = HANDLE_EINTR(sys_waitpid(child, &status, __WALL));
+
+  sys_close(fdes[1]);
+
+  if (r == -1) {
+    static const char msg[] = "ExceptionHandler::GenerateDump waitpid failed:";
+    logger::write(msg, sizeof(msg) - 1);
+    logger::write(strerror(errno), strlen(strerror(errno)));
+    logger::write("\n", 1);
+  }
+
+  bool success = r != -1 && WIFEXITED(status) && WEXITSTATUS(status) == 0;
+  if (callback_)
+    success =
+      callback_(minidump_descriptor_, callback_context_, addr_info, success);
+  return success;
+}
+
+// This function runs in a compromised context: see the top of the file.
+void ExceptionHandler::SendContinueSignalToChild() {
+  static const char okToContinueMessage = 'a';
+  int r;
+  r = HANDLE_EINTR(sys_write(fdes[1], &okToContinueMessage, sizeof(char)));
+  if (r == -1) {
+    static const char msg[] = "ExceptionHandler::SendContinueSignalToChild "
+                              "sys_write failed:";
+    logger::write(msg, sizeof(msg) - 1);
+    logger::write(strerror(errno), strlen(strerror(errno)));
+    logger::write("\n", 1);
+  }
+
+  const char* msg = "ExceptionHandler::SendContinueSignalToChild sent continue signal to child\n";
+  logger::write(msg, my_strlen(msg));
+}
+
+// This function runs in a compromised context: see the top of the file.
+// Runs on the cloned process.
+void ExceptionHandler::WaitForContinueSignal() {
+  int r;
+  char receivedMessage;
+
+  const char* waitMsg = "ExceptionHandler::WaitForContinueSignal waiting for continue signal...\n";
+  logger::write(waitMsg, my_strlen(waitMsg));
+
+  r = HANDLE_EINTR(sys_read(fdes[0], &receivedMessage, sizeof(char)));
+  if (r == -1) {
+    static const char msg[] = "ExceptionHandler::WaitForContinueSignal "
+                              "sys_read failed:";
+    logger::write(msg, sizeof(msg) - 1);
+    logger::write(strerror(errno), strlen(strerror(errno)));
+    logger::write("\n", 1);
+  }
+}
+
+// This function runs in a compromised context: see the top of the file.
+// Runs on the cloned process.
+bool ExceptionHandler::DoDump(pid_t crashing_process, const void* context,
+                              size_t context_size) {
+  const bool may_skip_dump =
+      minidump_descriptor_.skip_dump_if_principal_mapping_not_referenced();
+  const uintptr_t principal_mapping_address =
+      minidump_descriptor_.address_within_principal_mapping();
+  const bool sanitize_stacks = minidump_descriptor_.sanitize_stacks();
+  if (minidump_descriptor_.IsMicrodumpOnConsole()) {
+    return google_breakpad::WriteMicrodump(
+        crashing_process,
+        context,
+        context_size,
+        mapping_list_,
+        may_skip_dump,
+        principal_mapping_address,
+        sanitize_stacks,
+        *minidump_descriptor_.microdump_extra_info());
+  }
+  if (minidump_descriptor_.IsFD()) {
+    return google_breakpad::WriteMinidump(minidump_descriptor_.fd(),
+                                          minidump_descriptor_.size_limit(),
+                                          crashing_process,
+                                          context,
+                                          context_size,
+                                          mapping_list_,
+                                          app_memory_list_,
+                                          may_skip_dump,
+                                          principal_mapping_address,
+                                          sanitize_stacks);
+  }
+  return google_breakpad::WriteMinidump(minidump_descriptor_.path(),
+                                        minidump_descriptor_.size_limit(),
+                                        crashing_process,
+                                        context,
+                                        context_size,
+                                        mapping_list_,
+                                        app_memory_list_,
+                                        may_skip_dump,
+                                        principal_mapping_address,
+                                        sanitize_stacks);
+}
+
+// static
+bool ExceptionHandler::WriteMinidump(const string& dump_path,
+                                     MinidumpCallback callback,
+                                     void* callback_context) {
+  MinidumpDescriptor descriptor(dump_path);
+  ExceptionHandler eh(descriptor, NULL, callback, callback_context, false, -1);
+  return eh.WriteMinidump();
+}
+
+// In order to making using EBP to calculate the desired value for ESP
+// a valid operation, ensure that this function is compiled with a
+// frame pointer using the following attribute. This attribute
+// is supported on GCC but not on clang.
+#if defined(__i386__) && defined(__GNUC__) && !defined(__clang__)
+__attribute__((optimize("no-omit-frame-pointer")))
+#endif
+bool ExceptionHandler::WriteMinidump() {
+  if (!IsOutOfProcess() && !minidump_descriptor_.IsFD() &&
+      !minidump_descriptor_.IsMicrodumpOnConsole()) {
+    // Update the path of the minidump so that this can be called multiple times
+    // and new files are created for each minidump.  This is done before the
+    // generation happens, as clients may want to access the MinidumpDescriptor
+    // after this call to find the exact path to the minidump file.
+    minidump_descriptor_.UpdatePath();
+  } else if (minidump_descriptor_.IsFD()) {
+    // Reposition the FD to its beginning and resize it to get rid of the
+    // previous minidump info.
+    lseek(minidump_descriptor_.fd(), 0, SEEK_SET);
+    ignore_result(ftruncate(minidump_descriptor_.fd(), 0));
+  }
+
+  // Allow this process to be dumped.
+  sys_prctl(PR_SET_DUMPABLE, 1, 0, 0, 0);
+
+  CrashContext context;
+  int getcontext_result = getcontext(&context.context);
+  if (getcontext_result)
+    return false;
+
+#if defined(__i386__)
+  // In CPUFillFromUContext in minidumpwriter.cc the stack pointer is retrieved
+  // from REG_UESP instead of from REG_ESP. REG_UESP is the user stack pointer
+  // and it only makes sense when running in kernel mode with a different stack
+  // pointer. When WriteMiniDump is called during normal processing REG_UESP is
+  // zero which leads to bad minidump files.
+  if (!context.context.uc_mcontext.gregs[REG_UESP]) {
+    // If REG_UESP is set to REG_ESP then that includes the stack space for the
+    // CrashContext object in this function, which is about 128 KB. Since the
+    // Linux dumper only records 32 KB of stack this would mean that nothing
+    // useful would be recorded. A better option is to set REG_UESP to REG_EBP,
+    // perhaps with a small negative offset in case there is any code that
+    // objects to them being equal.
+    context.context.uc_mcontext.gregs[REG_UESP] =
+      context.context.uc_mcontext.gregs[REG_EBP] - 16;
+    // The stack saving is based off of REG_ESP so it must be set to match the
+    // new REG_UESP.
+    context.context.uc_mcontext.gregs[REG_ESP] =
+      context.context.uc_mcontext.gregs[REG_UESP];
+  }
+#endif
+
+#if !defined(__ARM_EABI__) && !defined(__aarch64__) && !defined(__mips__)
+  // FPU state is not part of ARM EABI ucontext_t.
+  memcpy(&context.float_state, context.context.uc_mcontext.fpregs,
+         sizeof(context.float_state));
+#endif
+  context.tid = sys_gettid();
+
+  // Add an exception stream to the minidump for better reporting.
+  memset(&context.siginfo, 0, sizeof(context.siginfo));
+  context.siginfo.si_signo = MD_EXCEPTION_CODE_LIN_DUMP_REQUESTED;
+#if defined(__i386__)
+  context.siginfo.si_addr =
+      reinterpret_cast<void*>(context.context.uc_mcontext.gregs[REG_EIP]);
+#elif defined(__x86_64__)
+  context.siginfo.si_addr =
+      reinterpret_cast<void*>(context.context.uc_mcontext.gregs[REG_RIP]);
+#elif defined(__arm__)
+  context.siginfo.si_addr =
+      reinterpret_cast<void*>(context.context.uc_mcontext.arm_pc);
+#elif defined(__aarch64__)
+  context.siginfo.si_addr =
+      reinterpret_cast<void*>(context.context.uc_mcontext.pc);
+#elif defined(__mips__)
+  context.siginfo.si_addr =
+      reinterpret_cast<void*>(context.context.uc_mcontext.pc);
+#else
+#error "This code has not been ported to your platform yet."
+#endif
+
+  // nullptr here for phc::AddrInfo* is ok because this is not a crash.
+  return GenerateDump(&context, nullptr);
+}
+
+void ExceptionHandler::AddMappingInfo(const string& name,
+                                      const wasteful_vector<uint8_t>& identifier,
+                                      uintptr_t start_address,
+                                      size_t mapping_size,
+                                      size_t file_offset) {
+  MappingInfo info;
+  info.start_addr = start_address;
+  info.size = mapping_size;
+  info.offset = file_offset;
+  strncpy(info.name, name.c_str(), sizeof(info.name) - 1);
+  info.name[sizeof(info.name) - 1] = '\0';
+
+  MappingEntry mapping;
+  mapping.first = info;
+  mapping.second.assign(identifier.begin(), identifier.end());
+  mapping_list_.push_back(mapping);
+}
+
+void ExceptionHandler::RegisterAppMemory(void* ptr, size_t length) {
+  AppMemoryList::iterator iter =
+    std::find(app_memory_list_.begin(), app_memory_list_.end(), ptr);
+  if (iter != app_memory_list_.end()) {
+    // Don't allow registering the same pointer twice.
+    return;
+  }
+
+  AppMemory app_memory;
+  app_memory.ptr = ptr;
+  app_memory.length = length;
+  app_memory_list_.push_back(app_memory);
+}
+
+void ExceptionHandler::UnregisterAppMemory(void* ptr) {
+  AppMemoryList::iterator iter =
+    std::find(app_memory_list_.begin(), app_memory_list_.end(), ptr);
+  if (iter != app_memory_list_.end()) {
+    app_memory_list_.erase(iter);
+  }
+}
+
+// static
+bool ExceptionHandler::WriteMinidumpForChild(pid_t child,
+                                             pid_t child_blamed_thread,
+                                             const string& dump_path,
+                                             MinidumpCallback callback,
+                                             void* callback_context) {
+  // This function is not run in a compromised context.
+  MinidumpDescriptor descriptor(dump_path);
+  descriptor.UpdatePath();
+#if defined(MOZ_OXIDIZED_BREAKPAD)
+  nsCString error_msg;
+  if (!write_minidump_linux(descriptor.path(), child, child_blamed_thread, &error_msg))
+      return false;
+#else
+  if (!google_breakpad::WriteMinidump(descriptor.path(),
+                                      child,
+                                      child_blamed_thread))
+      return false;
+#endif
+
+  // nullptr here for phc::AddrInfo* is ok because this is not a crash.
+  return callback ? callback(descriptor, callback_context, nullptr, true)
+                  : true;
+}
+
+void SetFirstChanceExceptionHandler(FirstChanceHandler callback) {
+  g_first_chance_handler_ = callback;
+}
+
+}  // namespace google_breakpad