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Diffstat (limited to 'breakpad/linux/exception_handler.cc')
| -rw-r--r-- | breakpad/linux/exception_handler.cc | 308 |
1 files changed, 308 insertions, 0 deletions
diff --git a/breakpad/linux/exception_handler.cc b/breakpad/linux/exception_handler.cc new file mode 100644 index 0000000..bbc6910 --- /dev/null +++ b/breakpad/linux/exception_handler.cc @@ -0,0 +1,308 @@ +// 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 |