sigchain: always call InitializeSignalChain on startup.
Processes that link against libsigchain because they might want to
dynamically load libart.so (e.g. surfaceflinger) might never explicitly
call InitializeSignalChain. In this scenario, the lazy initialization
that occurs when sigprocmask is called can happen at unexpected times,
such as from pthread_exit, leading to deadlocks or crashes.
Add __attribute__((constructor)) to InitializeSignalChain to have it be
automatically called upon process start. Keep the existing calls to it
in the wrapper functions in order to sidestep problems around static
initialization order.
Bug: https://issuetracker.google.com/37119593
Test: run-test 004-SignalTest
Test: m test-art-host
Test: m test-art-target
Change-Id: I7906c1f625ccca0350ea9310140a3f43a657be4c
diff --git a/sigchainlib/sigchain.cc b/sigchainlib/sigchain.cc
index f4799d2..13c03e8 100644
--- a/sigchainlib/sigchain.cc
+++ b/sigchainlib/sigchain.cc
@@ -93,6 +93,35 @@
static decltype(&sigaction) linked_sigaction;
static decltype(&sigprocmask) linked_sigprocmask;
+__attribute__((constructor)) static void InitializeSignalChain() {
+ static std::once_flag once;
+ std::call_once(once, []() {
+ void* 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)) {
+ fatal("Unable to find next sigaction in signal chain");
+ }
+ }
+
+ void* 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)) {
+ fatal("Unable to find next sigprocmask in signal chain");
+ }
+ }
+
+ linked_sigaction =
+ reinterpret_cast<decltype(linked_sigaction)>(linked_sigaction_sym);
+ linked_sigprocmask =
+ reinterpret_cast<decltype(linked_sigprocmask)>(linked_sigprocmask_sym);
+ });
+}
+
+
static pthread_key_t GetHandlingSignalKey() {
static pthread_key_t key;
static std::once_flag once;
@@ -263,6 +292,8 @@
}
extern "C" int sigaction(int signal, const struct sigaction* new_action, struct sigaction* old_action) {
+ InitializeSignalChain();
+
// 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
@@ -285,11 +316,12 @@
// 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.
- InitializeSignalChain();
return linked_sigaction(signal, new_action, old_action);
}
extern "C" sighandler_t signal(int signo, sighandler_t handler) {
+ InitializeSignalChain();
+
if (signo < 0 || signo > _NSIG) {
errno = EINVAL;
return SIG_ERR;
@@ -311,7 +343,6 @@
// 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.
- InitializeSignalChain();
if (linked_sigaction(signo, &sa, &sa) == -1) {
return SIG_ERR;
}
@@ -321,11 +352,15 @@
#if !defined(__LP64__)
extern "C" sighandler_t bsd_signal(int signo, sighandler_t handler) {
+ InitializeSignalChain();
+
return signal(signo, handler);
}
#endif
extern "C" int sigprocmask(int how, const sigset_t* bionic_new_set, sigset_t* bionic_old_set) {
+ InitializeSignalChain();
+
// When inside a signal handler, forward directly to the actual sigprocmask.
if (GetHandlingSignal()) {
return linked_sigprocmask(how, bionic_new_set, bionic_old_set);
@@ -348,47 +383,12 @@
new_set_ptr = &tmpset;
}
- InitializeSignalChain();
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.
- static bool initialized = false;
- if (initialized) {
- // Don't initialize twice.
- return;
- }
-
- void* 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)) {
- fatal("Unable to find next sigaction in signal chain");
- }
- }
-
- void* 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)) {
- fatal("Unable to find next sigprocmask in signal chain");
- }
- }
-
- linked_sigaction = reinterpret_cast<decltype(linked_sigaction)>(linked_sigaction_sym);
- linked_sigprocmask = reinterpret_cast<decltype(linked_sigprocmask)>(linked_sigprocmask_sym);
- initialized = true;
-}
-
extern "C" void AddSpecialSignalHandlerFn(int signal, SpecialSignalHandlerFn fn) {
+ InitializeSignalChain();
+
if (signal <= 0 || signal >= _NSIG) {
fatal("Invalid signal %d", signal);
}
@@ -399,6 +399,8 @@
}
extern "C" void RemoveSpecialSignalHandlerFn(int signal, SpecialSignalHandlerFn fn) {
+ InitializeSignalChain();
+
if (signal <= 0 || signal >= _NSIG) {
fatal("Invalid signal %d", signal);
}
@@ -407,14 +409,16 @@
}
extern "C" void EnsureFrontOfChain(int signal) {
+ InitializeSignalChain();
+
if (signal <= 0 || signal >= _NSIG) {
fatal("Invalid signal %d", signal);
}
// Read the current action without looking at the chain, it should be the expected action.
struct sigaction current_action;
- InitializeSignalChain();
linked_sigaction(signal, nullptr, ¤t_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 != SignalChain::Handler) {