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/*
* Copyright (C) 2014 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.
*/
#ifdef HAVE_ANDROID_OS
#include <android/log.h>
#else
#include <stdarg.h>
#include <iostream>
#endif
#include <dlfcn.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include "sigchain.h"
#if defined(__APPLE__)
#define _NSIG NSIG
#define sighandler_t sig_t
#endif
namespace art {
typedef int (*SigActionFnPtr)(int, const struct sigaction*, struct sigaction*);
class SignalAction {
public:
SignalAction() : claimed_(false), uses_old_style_(false) {
}
// Claim the signal and keep the action specified.
void Claim(const struct sigaction& action) {
action_ = action;
claimed_ = true;
}
// Unclaim the signal and restore the old action.
void Unclaim(int signal) {
claimed_ = false;
sigaction(signal, &action_, nullptr); // Restore old action.
}
// Get the action associated with this signal.
const struct sigaction& GetAction() const {
return action_;
}
// Is the signal claimed?
bool IsClaimed() const {
return claimed_;
}
// Change the recorded action to that specified.
// If oldstyle is true then this action is from an older style signal()
// call as opposed to sigaction(). In this case the sa_handler is
// used when invoking the user's handler.
void SetAction(const struct sigaction& action, bool oldstyle) {
action_ = action;
uses_old_style_ = oldstyle;
}
bool OldStyle() const {
return uses_old_style_;
}
private:
struct sigaction action_; // Action to be performed.
bool claimed_; // Whether signal is claimed or not.
bool uses_old_style_; // Action is created using signal(). Use sa_handler.
};
// User's signal handlers
static SignalAction user_sigactions[_NSIG];
static bool initialized;
static void* linked_sigaction_sym;
static void* linked_sigprocmask_sym;
static void log(const char* format, ...) {
char buf[256];
va_list ap;
va_start(ap, format);
vsnprintf(buf, sizeof(buf), format, ap);
#ifdef HAVE_ANDROID_OS
__android_log_write(ANDROID_LOG_ERROR, "libsigchain", buf);
#else
std::cout << buf << "\n";
#endif
va_end(ap);
}
static void CheckSignalValid(int signal) {
if (signal <= 0 || signal >= _NSIG) {
log("Invalid signal %d", signal);
abort();
}
}
// Claim a signal chain for a particular signal.
extern "C" void ClaimSignalChain(int signal, struct sigaction* oldaction) {
CheckSignalValid(signal);
user_sigactions[signal].Claim(*oldaction);
}
extern "C" void UnclaimSignalChain(int signal) {
CheckSignalValid(signal);
user_sigactions[signal].Unclaim(signal);
}
// Invoke the user's signal handler.
extern "C" void InvokeUserSignalHandler(int sig, siginfo_t* info, void* context) {
// Check the arguments.
CheckSignalValid(sig);
// The signal must have been claimed in order to get here. Check it.
if (!user_sigactions[sig].IsClaimed()) {
abort();
}
const struct sigaction& action = user_sigactions[sig].GetAction();
if (user_sigactions[sig].OldStyle()) {
if (action.sa_handler != nullptr) {
action.sa_handler(sig);
} else {
signal(sig, SIG_DFL);
raise(sig);
}
} else {
if (action.sa_sigaction != nullptr) {
action.sa_sigaction(sig, info, context);
} else {
signal(sig, SIG_DFL);
raise(sig);
}
}
}
extern "C" void EnsureFrontOfChain(int signal, struct sigaction* expected_action) {
CheckSignalValid(signal);
// Read the current action without looking at the chain, it should be the expected action.
SigActionFnPtr linked_sigaction = reinterpret_cast<SigActionFnPtr>(linked_sigaction_sym);
struct sigaction current_action;
linked_sigaction(signal, nullptr, &current_action);
// If the sigactions don't match then we put the current action on the chain and make ourself as
// the main action.
if (current_action.sa_sigaction != expected_action->sa_sigaction) {
log("Warning: Unexpected sigaction action found %p\n", current_action.sa_sigaction);
user_sigactions[signal].Claim(current_action);
linked_sigaction(signal, expected_action, nullptr);
}
}
extern "C" int sigaction(int signal, const struct sigaction* new_action, struct sigaction* old_action) {
// If this signal has been claimed as a signal chain, record the user's
// action but don't pass it on to the kernel.
// Note that we check that the signal number is in range here. An out of range signal
// number should behave exactly as the libc sigaction.
if (signal > 0 && signal < _NSIG && user_sigactions[signal].IsClaimed() &&
(new_action == nullptr || new_action->sa_handler != SIG_DFL)) {
struct sigaction saved_action = user_sigactions[signal].GetAction();
if (new_action != nullptr) {
user_sigactions[signal].SetAction(*new_action, false);
}
if (old_action != nullptr) {
*old_action = saved_action;
}
return 0;
}
// Will only get here if the signal chain has not been claimed. We want
// to pass the sigaction on to the kernel via the real sigaction in libc.
if (linked_sigaction_sym == nullptr) {
// Perform lazy initialization.
// This will only occur outside of a signal context since we have
// not been initialized and therefore cannot be within the ART
// runtime.
InitializeSignalChain();
}
if (linked_sigaction_sym == nullptr) {
log("Unable to find next sigaction in signal chain");
abort();
}
SigActionFnPtr linked_sigaction = reinterpret_cast<SigActionFnPtr>(linked_sigaction_sym);
return linked_sigaction(signal, new_action, old_action);
}
extern "C" sighandler_t signal(int signal, sighandler_t handler) {
struct sigaction sa;
sigemptyset(&sa.sa_mask);
sa.sa_handler = handler;
sa.sa_flags = SA_RESTART;
sighandler_t oldhandler;
// If this signal has been claimed as a signal chain, record the user's
// action but don't pass it on to the kernel.
// Note that we check that the signal number is in range here. An out of range signal
// number should behave exactly as the libc sigaction.
if (signal > 0 && signal < _NSIG && user_sigactions[signal].IsClaimed() && handler != SIG_DFL) {
oldhandler = reinterpret_cast<sighandler_t>(user_sigactions[signal].GetAction().sa_handler);
user_sigactions[signal].SetAction(sa, true);
return oldhandler;
}
// Will only get here if the signal chain has not been claimed. We want
// to pass the sigaction on to the kernel via the real sigaction in libc.
if (linked_sigaction_sym == nullptr) {
// Perform lazy initialization.
InitializeSignalChain();
}
if (linked_sigaction_sym == nullptr) {
log("Unable to find next sigaction in signal chain");
abort();
}
typedef int (*SigAction)(int, const struct sigaction*, struct sigaction*);
SigAction linked_sigaction = reinterpret_cast<SigAction>(linked_sigaction_sym);
if (linked_sigaction(signal, &sa, &sa) == -1) {
return SIG_ERR;
}
return reinterpret_cast<sighandler_t>(sa.sa_handler);
}
extern "C" int sigprocmask(int how, const sigset_t* bionic_new_set, sigset_t* bionic_old_set) {
const sigset_t* new_set_ptr = bionic_new_set;
sigset_t tmpset;
if (bionic_new_set != nullptr) {
tmpset = *bionic_new_set;
if (how == SIG_BLOCK) {
// Don't allow claimed signals in the mask. If a signal chain has been claimed
// we can't allow the user to block that signal.
for (int i = 0 ; i < _NSIG; ++i) {
if (user_sigactions[i].IsClaimed() && sigismember(&tmpset, i)) {
sigdelset(&tmpset, i);
}
}
}
new_set_ptr = &tmpset;
}
if (linked_sigprocmask_sym == nullptr) {
// Perform lazy initialization.
InitializeSignalChain();
}
if (linked_sigprocmask_sym == nullptr) {
log("Unable to find next sigprocmask in signal chain");
abort();
}
typedef int (*SigProcMask)(int how, const sigset_t*, sigset_t*);
SigProcMask linked_sigprocmask= reinterpret_cast<SigProcMask>(linked_sigprocmask_sym);
return linked_sigprocmask(how, new_set_ptr, bionic_old_set);
}
extern "C" void InitializeSignalChain() {
// Warning.
// Don't call this from within a signal context as it makes calls to
// dlsym. Calling into the dynamic linker will result in locks being
// taken and if it so happens that a signal occurs while one of these
// locks is already taken, dlsym will block trying to reenter a
// mutex and we will never get out of it.
if (initialized) {
// Don't initialize twice.
return;
}
linked_sigaction_sym = dlsym(RTLD_NEXT, "sigaction");
if (linked_sigaction_sym == nullptr) {
linked_sigaction_sym = dlsym(RTLD_DEFAULT, "sigaction");
if (linked_sigaction_sym == nullptr ||
linked_sigaction_sym == reinterpret_cast<void*>(sigaction)) {
linked_sigaction_sym = nullptr;
}
}
linked_sigprocmask_sym = dlsym(RTLD_NEXT, "sigprocmask");
if (linked_sigprocmask_sym == nullptr) {
linked_sigprocmask_sym = dlsym(RTLD_DEFAULT, "sigprocmask");
if (linked_sigprocmask_sym == nullptr ||
linked_sigprocmask_sym == reinterpret_cast<void*>(sigprocmask)) {
linked_sigprocmask_sym = nullptr;
}
}
initialized = true;
}
} // namespace art