compiler-rt/test/sanitizer_common/TestCases/Linux/signal_segv_handler.cpp

   1 // RUN: %clangxx -O1 %s -o %t && env TSAN_OPTIONS="flush_memory_ms=1 memory_limit_mb=1" %run %t 2>&1 | FileCheck %s
   2
   3 // JVM uses SEGV to preempt threads. All threads do a load from a known address
   4 // periodically. When runtime needs to preempt threads, it unmaps the page.
   5 // Threads start triggering SEGV one by one. The signal handler blocks
   6 // threads while runtime does its thing. Then runtime maps the page again
   7 // and resumes the threads.
   8 // Previously this pattern conflicted with stop-the-world machinery,
   9 // because it briefly reset SEGV handler to SIG_DFL.
  10 // As the consequence JVM just silently died.
  11
  12 // This test sets memory flushing rate to maximum, then does series of
  13 // "benign" SEGVs that are handled by signal handler, and ensures that
  14 // the process survive.
  15
  16 #include <assert.h>
  17 #include <signal.h>
  18 #include <stdio.h>
  19 #include <stdlib.h>
  20 #include <string.h>
  21 #include <sys/mman.h>
  22 #include <unistd.h>
  23
  24 unsigned long page_size;
  25 void *guard;
  26
  27 void handler(int signo, siginfo_t *info, void *uctx) {
  28   mprotect(guard, page_size, PROT_READ | PROT_WRITE);
  29 }
  30
  31 int main() {
  32   page_size = sysconf(_SC_PAGESIZE);
  33   struct sigaction a, old;
  34   memset(&a, 0, sizeof(a));
  35   memset(&old, 0, sizeof(old));
  36   a.sa_sigaction = handler;
  37   a.sa_flags = SA_SIGINFO;
  38   sigaction(SIGSEGV, &a, &old);
  39
  40   memset(&a, 0, sizeof(a));
  41   sigaction(SIGSEGV, 0, &a);
  42   assert(a.sa_sigaction == handler);
  43   assert(a.sa_flags & SA_SIGINFO);
  44
  45   guard = mmap(0, 3 * page_size, PROT_NONE, MAP_ANON | MAP_PRIVATE, -1, 0);
  46   guard = (char*)guard + page_size;  // work around a kernel bug
  47   for (int i = 0; i < 1000000; i++) {
  48     mprotect(guard, page_size, PROT_NONE);
  49     *(int*)guard = 1;
  50   }
  51   sigaction(SIGSEGV, &old, 0);
  52   fprintf(stderr, "DONE\n");
  53 }
  54
  55 // CHECK: DONE