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/*
* Copyright (C) 2013 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#define _GNU_SOURCE 1
#include <errno.h>
#include <stdint.h>
#include <string.h>
#include <sys/param.h>
#include <sys/ptrace.h>
#include <sys/types.h>
#include <ucontext.h>
#include <unistd.h>
#include <string>
#include <backtrace/Backtrace.h>
#include <backtrace/BacktraceMap.h>
#include <cutils/threads.h>
#include "BacktraceCurrent.h"
#include "BacktraceLog.h"
#include "ThreadEntry.h"
#include "thread_utils.h"
bool BacktraceCurrent::ReadWord(uintptr_t ptr, word_t* out_value) {
if (!VerifyReadWordArgs(ptr, out_value)) {
return false;
}
backtrace_map_t map;
FillInMap(ptr, &map);
if (BacktraceMap::IsValid(map) && map.flags & PROT_READ) {
*out_value = *reinterpret_cast<word_t*>(ptr);
return true;
} else {
BACK_LOGW("pointer %p not in a readable map", reinterpret_cast<void*>(ptr));
*out_value = static_cast<word_t>(-1);
return false;
}
}
size_t BacktraceCurrent::Read(uintptr_t addr, uint8_t* buffer, size_t bytes) {
backtrace_map_t map;
FillInMap(addr, &map);
if (!BacktraceMap::IsValid(map) || !(map.flags & PROT_READ)) {
return 0;
}
bytes = MIN(map.end - addr, bytes);
memcpy(buffer, reinterpret_cast<uint8_t*>(addr), bytes);
return bytes;
}
bool BacktraceCurrent::Unwind(size_t num_ignore_frames, ucontext_t* ucontext) {
if (GetMap() == nullptr) {
// Without a map object, we can't do anything.
return false;
}
if (ucontext) {
return UnwindFromContext(num_ignore_frames, ucontext);
}
if (Tid() != gettid()) {
return UnwindThread(num_ignore_frames);
}
return UnwindFromContext(num_ignore_frames, nullptr);
}
bool BacktraceCurrent::DiscardFrame(const backtrace_frame_data_t& frame) {
if (BacktraceMap::IsValid(frame.map)) {
const std::string library = basename(frame.map.name.c_str());
if (library == "libunwind.so" || library == "libbacktrace.so") {
return true;
}
}
return false;
}
static pthread_mutex_t g_sigaction_mutex = PTHREAD_MUTEX_INITIALIZER;
static void SignalHandler(int, siginfo_t*, void* sigcontext) {
ThreadEntry* entry = ThreadEntry::Get(getpid(), gettid(), false);
if (!entry) {
BACK_LOGE("pid %d, tid %d entry not found", getpid(), gettid());
return;
}
entry->CopyUcontextFromSigcontext(sigcontext);
// Indicate the ucontext is now valid.
entry->Wake();
// Pause the thread until the unwind is complete. This avoids having
// the thread run ahead causing problems.
// The number indicates that we are waiting for the second Wake() call
// overall which is made by the thread requesting an unwind.
if (entry->Wait(2)) {
// Do not remove the entry here because that can result in a deadlock
// if the code cannot properly send a signal to the thread under test.
entry->Wake();
} else {
// At this point, it is possible that entry has been freed, so just exit.
BACK_LOGE("Timed out waiting for unwind thread to indicate it completed.");
}
}
bool BacktraceCurrent::UnwindThread(size_t num_ignore_frames) {
// Prevent multiple threads trying to set the trigger action on different
// threads at the same time.
pthread_mutex_lock(&g_sigaction_mutex);
ThreadEntry* entry = ThreadEntry::Get(Pid(), Tid());
entry->Lock();
struct sigaction act, oldact;
memset(&act, 0, sizeof(act));
act.sa_sigaction = SignalHandler;
act.sa_flags = SA_RESTART | SA_SIGINFO | SA_ONSTACK;
sigemptyset(&act.sa_mask);
if (sigaction(THREAD_SIGNAL, &act, &oldact) != 0) {
BACK_LOGE("sigaction failed: %s", strerror(errno));
ThreadEntry::Remove(entry);
pthread_mutex_unlock(&g_sigaction_mutex);
return false;
}
if (tgkill(Pid(), Tid(), THREAD_SIGNAL) != 0) {
BACK_LOGE("tgkill %d failed: %s", Tid(), strerror(errno));
sigaction(THREAD_SIGNAL, &oldact, nullptr);
ThreadEntry::Remove(entry);
pthread_mutex_unlock(&g_sigaction_mutex);
return false;
}
// Wait for the thread to get the ucontext. The number indicates
// that we are waiting for the first Wake() call made by the thread.
bool wait_completed = entry->Wait(1);
// After the thread has received the signal, allow other unwinders to
// continue.
sigaction(THREAD_SIGNAL, &oldact, nullptr);
pthread_mutex_unlock(&g_sigaction_mutex);
bool unwind_done = false;
if (wait_completed) {
unwind_done = UnwindFromContext(num_ignore_frames, entry->GetUcontext());
// Tell the signal handler to exit and release the entry.
entry->Wake();
// Wait for the thread to indicate it is done with the ThreadEntry.
if (!entry->Wait(3)) {
// Send a warning, but do not mark as a failure to unwind.
BACK_LOGW("Timed out waiting for signal handler to indicate it finished.");
}
} else {
BACK_LOGE("Timed out waiting for signal handler to get ucontext data.");
}
ThreadEntry::Remove(entry);
return unwind_done;
}
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