sanitizer_common: fix and re-enable signal_segv_handler test

[dvyukov]

Summary

struct sigaction was not initialized. As the result if SA_RESETHAND is set in sa_flags, then the handler is reset after first invocation leading to crash.
Initialize struct sigaction to zero.
Ironically, the test was run under msan all the time.

[eugenis]

LGTM
Thanks!

[dvyukov]

Please add msan interceptor for sigaction.

[dvyukov]

Submitted in 240965.

[eugenis]

Just saw this test crash (SEGV) at r240965 (i.e. with this patch) in ninja check-all, but could not reproduce in an individual run.

TestCases/Linux/signal_segv_handler.cc

 // RUN: %clangxx -O1 %s -o %t && TSAN_OPTIONS="flush_memory_ms=1 memory_limit_mb=1" ASAN_OPTIONS="handle_segv=0 allow_user_segv_handler=1" %run %t 2>&1 | FileCheck %s
 
 // JVM uses SEGV to preempt threads. All threads do a load from a known address
 // periodically. When runtime needs to preempt threads, it unmaps the page.
 // Threads start triggering SEGV one by one. The signal handler blocks
 // threads while runtime does its thing. Then runtime maps the page again
 // and resumes the threads.
 // Previously this pattern conflicted with stop-the-world machinery,
 // because it briefly reset SEGV handler to SIG_DFL.
 // As the consequence JVM just silently died.
 
 // This test sets memory flushing rate to maximum, then does series of
 // "benign" SEGVs that are handled by signal handler, and ensures that
 // the process survive.
 
-// REQUIRES: disabled
-
 #include <stdio.h>
 #include <stdlib.h>
 #include <signal.h>
 #include <sys/mman.h>
+#include <string.h>
 
 void *guard;
 
 void handler(int signo, siginfo_t *info, void *uctx) {
   mprotect(guard, 4096, PROT_READ | PROT_WRITE);
 }
 
 int main() {
   struct sigaction a, old;
+  memset(&a, sizeof(a));
+  memset(&old, sizeof(old));
   a.sa_sigaction = handler;
   a.sa_flags = SA_SIGINFO;
   sigaction(SIGSEGV, &a, &old);
   guard = mmap(0, 4096, PROT_NONE, MAP_ANON | MAP_PRIVATE, -1, 0);
   for (int i = 0; i < 1000000; i++) {
     mprotect(guard, 4096, PROT_NONE);
     *(int*)guard = 1;
   }
   sigaction(SIGSEGV, &old, 0);
   fprintf(stderr, "DONE\n");
 }
 
 // CHECK: DONE