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Commit 10ab87f6 authored by Christopher Ferris's avatar Christopher Ferris
Browse files

Restore errno in signal handlers. 

There was a problem where errno could be set in a signal handler
and cause bugs if other system calls were interrupted.

There isn't strong evidence this is causing any issues, but add this
proactively.

Bug: 31448909

Test: Ran the backtrace unit tests, backtraces few random processes,
Test: forced the ANR path for some zygote based processes.
Test: Ran the art ThreadStress test a few times.
Change-Id: I5abc9e330a5e86cea7015e2362f66044c6bc37d0
parent c1b3c8ef

libbacktrace/BacktraceCurrent.cpp

+20 −0
Original line number Diff line number Diff line
@@ -95,11 +95,31 @@ bool BacktraceCurrent::DiscardFrame(const backtrace_frame_data_t& frame) { 


static pthread_mutex_t g_sigaction_mutex = PTHREAD_MUTEX_INITIALIZER;



// Since errno is stored per thread, changing it in the signal handler

// modifies the value on the thread in which the signal handler executes.

// If a signal occurs between a call and an errno check, it's possible

// to get the errno set here. Always save and restore it just in case

// code would modify it.

class ErrnoRestorer {

 public:

  ErrnoRestorer() : saved_errno_(errno) {}

  ~ErrnoRestorer() {

    errno = saved_errno_;

  }



 private:

  int saved_errno_;

};



static void SignalLogOnly(int, siginfo_t*, void*) {

  ErrnoRestorer restore;



  BACK_LOGE("pid %d, tid %d: Received a spurious signal %d\n", getpid(), gettid(), THREAD_SIGNAL);

}



static void SignalHandler(int, siginfo_t*, void* sigcontext) {

  ErrnoRestorer restore;



  ThreadEntry* entry = ThreadEntry::Get(getpid(), gettid(), false);

  if (!entry) {

    BACK_LOGE("pid %d, tid %d entry not found", getpid(), gettid());