Linux: Add Breakpad client.

breakpad/linux/exception_handler.cc

Index: breakpad/linux/exception_handler.cc
diff --git a/breakpad/linux/exception_handler.cc b/breakpad/linux/exception_handler.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.
+
+// 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 "breakpad/linux/exception_handler.h"
+
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <errno.h>
+#include <signal.h>
+#include <sys/signal.h>
+#include <sys/ucontext.h>
+#include <sys/user.h>
+#include <sys/syscall.h>
+#include <sys/wait.h>
+#include <sched.h>
+
+#include "breakpad/linux/linux_syscall_support.h"
+#include "breakpad/linux/memory.h"
+#include "breakpad/linux/minidump_writer.h"
+#include "common/linux/guid_creator.h"
+
+// A wrapper for the tgkill syscall: send a signal to a specific thread.
+static int tgkill(pid_t tgid, pid_t tid, int sig) {
+  syscall(__NR_tgkill, tgid, tid, sig);
+}
+
+namespace google_breakpad {
+
+// 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.
+static const int kExceptionSignals[] = {
+  SIGSEGV, SIGABRT, SIGFPE, SIGILL, SIGBUS, -1
+};
+
+// We can stack multiple exception handlers. In that case, this is the global
+// which holds the stack.
+std::vector<ExceptionHandler*>* ExceptionHandler::handler_stack_ = NULL;
+unsigned ExceptionHandler::handler_stack_index_ = 0;
+pthread_mutex_t ExceptionHandler::handler_stack_mutex_ =
+    PTHREAD_MUTEX_INITIALIZER;
+
+// Runs before crashing: normal context.
+ExceptionHandler::ExceptionHandler(const std::string &dump_path,
+                                   FilterCallback filter,
+                                   MinidumpCallback callback,
+                                   void *callback_context,
+                                   bool install_handler)
+    : filter_(filter),
+      callback_(callback),
+      callback_context_(callback_context),
+      dump_path_(),
+      handler_installed_(install_handler),
+      crash_handler_(NULL) {
+  set_dump_path(dump_path);
+
+  if (install_handler) {
+    InstallHandlers();
+
+    pthread_mutex_lock(&handler_stack_mutex_);
+      if (handler_stack_ == NULL)
+        handler_stack_ = new std::vector<ExceptionHandler *>;
+      handler_stack_->push_back(this);
+    pthread_mutex_unlock(&handler_stack_mutex_);
+  }
+}
+
+// Runs before crashing: normal context.
+ExceptionHandler::~ExceptionHandler() {
+  UninstallHandlers();
+}
+
+// Runs before crashing: normal context.
+bool ExceptionHandler::InstallHandlers() {
+  // We run the signal handlers on an alternative stack because we might have
+  // crashed because of a stack overflow.
+
+  // We use this value rather than SIGSTKSZ because we would end up overrunning
+  // such a small stack.
+  static const unsigned kSigStackSize = 8192;
+
+  signal_stack = malloc(kSigStackSize);
+  stack_t stack;
+  memset(&stack, 0, sizeof(stack));
+  stack.ss_sp = signal_stack;
+  stack.ss_size = kSigStackSize;
+
+  if (sigaltstack(&stack, NULL) == -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 (unsigned i = 0; kExceptionSignals[i] != -1; ++i)
+    sigaddset(&sa.sa_mask, kExceptionSignals[i]);
+
+  sa.sa_sigaction = SignalHandler;
+  sa.sa_flags = SA_ONSTACK | SA_SIGINFO;
+
+  for (unsigned i = 0; kExceptionSignals[i] != -1; ++i) {
+    struct sigaction* old = new struct sigaction;
+    if (sigaction(kExceptionSignals[i], &sa, old) == -1)
+      return false;
+    old_handlers_.push_back(std::make_pair(kExceptionSignals[i], old));
+  }
+}
+
+// Runs before crashing: normal context.
+void ExceptionHandler::UninstallHandlers() {
+  for (unsigned i = 0; i < old_handlers_.size(); ++i) {
+    struct sigaction *action =
+        reinterpret_cast<struct sigaction*>(old_handlers_[i].second);
+    sigaction(old_handlers_[i].first, action, NULL);
+    delete action;
+  }
+
+  old_handlers_.clear();
+}
+
+// Runs before crashing: normal context.
+void ExceptionHandler::UpdateNextID() {
+  GUID guid;
+  char guid_str[kGUIDStringLength + 1];
+  if (CreateGUID(&guid) && GUIDToString(&guid, guid_str, sizeof(guid_str))) {
+    next_minidump_id_ = guid_str;
+    next_minidump_id_c_ = next_minidump_id_.c_str();
+
+    char minidump_path[PATH_MAX];
+    snprintf(minidump_path, sizeof(minidump_path), "%s/%s.dmp",
+             dump_path_c_,
+             guid_str);
+
+    next_minidump_path_ = minidump_path;
+    next_minidump_path_c_ = next_minidump_path_.c_str();
+  }
+}
+
+// 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) {
+  // All the exception signals are blocked at this point.
+
+  pthread_mutex_lock(&handler_stack_mutex_);
+
+  if (!handler_stack_->size()) {
+    pthread_mutex_unlock(&handler_stack_mutex_);
+    return;
+  }
+
+  for (int i = handler_stack_->size() - 1; i >= 0; --i) {
+    if ((*handler_stack_)[i]->HandleSignal(sig, info, uc)) {
+      // successfully handled: We are in an invalid state since an exception
+      // signal has been delivered. We don't call the exit handlers because
+      // they could end up corrupting on-disk state.
+      break;
+    }
+  }
+
+  pthread_mutex_unlock(&handler_stack_mutex_);
+
+  // Terminate ourselves with the same signal so that our parent knows that we
+  // crashed. The default action for all the signals which we catch is Core, so
+  // this is the end of us.
+  signal(sig, SIG_DFL);
+  tgkill(getpid(), sys_gettid(), sig);
+
+  // not reached.
+}
+
+struct ThreadArgument {
+  pid_t pid;  // the crashing process
+  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);
+  return thread_arg->handler->DoDump(thread_arg->pid, thread_arg->context,
+                                     thread_arg->context_size) == false;
+}
+
+// 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) {
+  if (filter_ && !filter_(callback_context_))
+    return false;
+
+  CrashContext context;
+  memcpy(&context.siginfo, info, sizeof(siginfo_t));
+  memcpy(&context.context, uc, sizeof(struct ucontext));
+  context.tid = sys_gettid();
+
+  if (crash_handler_ && crash_handler_(&context, sizeof(context),
+                                       callback_context_))
+    return true;
+
+  PageAllocator allocator;
+  void* const stack = allocator.Alloc(8000);
+
+  ThreadArgument thread_arg;
+  thread_arg.handler = this;
+  thread_arg.pid = getpid();
+  thread_arg.context = &context;
+  thread_arg.context_size = sizeof(context);
+
+  const pid_t child = sys_clone(
+      ThreadEntry, stack, CLONE_FILES | CLONE_FS | CLONE_UNTRACED,
+      &thread_arg, NULL, NULL, NULL);
+  int r, status;
+  do {
+    r = sys_waitpid(child, &status, __WALL);
+  } while (r == -1 && errno == EINTR);
+
+  if (r == -1) {
+    static const char msg[] = "ExceptionHandler::HandleSignal: waitpid failed:";
+    sys_write(2, msg, sizeof(msg) - 1);
+    sys_write(2, strerror(errno), strlen(strerror(errno)));
+    sys_write(2, "\n", 1);
+  }
+
+  bool success = r != -1 && WIFEXITED(status) && WEXITSTATUS(status) == 0;
+
+  if (callback_)
+    success = callback_(dump_path_c_, next_minidump_id_c_,
+                        callback_context_, success);
+
+  return success;
+}
+
+// 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) {
+  return google_breakpad::WriteMinidump(
+      next_minidump_path_c_, crashing_process, context, context_size);
+}
+
+}  // namespace google_breakpad