[esan] Ensure internal_sigaction() bypasses interceptors

Summary:
Implements real_sigaction() which it turns out is required for
internal_sigaction() to bypass the libc interceptors.

Without real_sigaction(), our internal_sigaction() calls during init happen
to work due to the EsanDuringInit check in COMMON_INTERCEPTOR_ENTER (though
even here it does not feel right for an "internal_" call to go through the
interceptor).  The real problem is when we call internal_sigaction() after
we're initialized, which only happens on an unhandled SIGSEGV for which the
app has no handler: then we'll spin in an infinite loop as our attempts to
remove our own handler repeatedly fail.  It's not easy to add a test for
that, unfortunately.

Reviewers: aizatsky

Subscribers: vitalybuka, zhaoqin, kcc, eugenis, llvm-commits, kubabrecka

Differential Revision: http://reviews.llvm.org/D20832

llvm-svn: 271626

compiler-rt/lib/esan/esan_interceptors.cpp

@@ -373,6 +373,8 @@ INTERCEPTOR(signal_handler_t, signal, int signum, signal_handler_t handler) {
 #endif
 
 #if SANITIZER_LINUX
+DECLARE_REAL(int, sigaction, int signum, const struct sigaction *act,
+             struct sigaction *oldact)
 INTERCEPTOR(int, sigaction, int signum, const struct sigaction *act,
             struct sigaction *oldact) {
   void *ctx;
@@ -382,6 +384,15 @@ INTERCEPTOR(int, sigaction, int signum, const struct sigaction *act,
   else
     return REAL(sigaction)(signum, act, oldact);
 }
+
+// This is required to properly use internal_sigaction.
+namespace __sanitizer {
+int real_sigaction(int signum, const void *act, void *oldact) {
+  return REAL(sigaction)(signum, (const struct sigaction *)act,
+                         (struct sigaction *)oldact);
+}
+} // namespace __sanitizer
+
 #define ESAN_MAYBE_INTERCEPT_SIGACTION INTERCEPT_FUNCTION(sigaction)
 #else
 #error Platform not supported

compiler-rt/lib/sanitizer_common/sanitizer_posix.h

@@ -78,6 +78,8 @@ int real_pthread_join(void *th, void **ret);
 
 int my_pthread_attr_getstack(void *attr, void **addr, uptr *size);
 
+// A routine named real_sigaction() must be implemented by each sanitizer in
+// order for internal_sigaction() to bypass interceptors.
 int internal_sigaction(int signum, const void *act, void *oldact);
 void internal_sigfillset(__sanitizer_sigset_t *set);