1// RUN: %clang_tsan -O1 %s -o %t && %run %t 2>&1 | FileCheck %s
2#include "test.h"
3
4// Test case https://github.com/google/sanitizers/issues/494
5// Tsan sees false HB edge on address pointed to by syncp variable.
6// It is false because when acquire is done syncp points to a var in one frame,
7// and during release it points to a var in a different frame.
8// The code is somewhat tricky because it prevents compiler from optimizing
9// our accesses away, structured to not introduce other data races and
10// not introduce other synchronization, and to arrange the vars in different
11// frames to occupy the same address.
12
13// The data race CHECK-NOT below actually must be CHECK, because the program
14// does contain the data race on global.
15
16// CHECK-NOT: WARNING: ThreadSanitizer: data race
17// CHECK: DONE
18
19long global;
20long *syncp;
21long *addr;
22long sink;
23
24void *Thread(void *x) {
25  while (__atomic_load_n(&syncp, __ATOMIC_ACQUIRE) == 0)
26    usleep(1000);  // spin wait
27  global = 42;
28  __atomic_store_n(syncp, 1, __ATOMIC_RELEASE);
29  __atomic_store_n(&syncp, 0, __ATOMIC_RELAXED);
30  return NULL;
31}
32
33void __attribute__((noinline)) foobar() {
34  __attribute__((aligned(64))) long s;
35
36  addr = &s;
37  __atomic_store_n(&s, 0, __ATOMIC_RELAXED);
38  __atomic_store_n(&syncp, &s, __ATOMIC_RELEASE);
39  while (__atomic_load_n(&syncp, __ATOMIC_RELAXED) != 0)
40    usleep(1000);  // spin wait
41}
42
43void __attribute__((noinline)) barfoo() {
44  __attribute__((aligned(64))) long s;
45
46  if (addr != &s) {
47    printf("address mismatch addr=%p &s=%p\n", addr, &s);
48    exit(1);
49  }
50  __atomic_store_n(&addr, &s, __ATOMIC_RELAXED);
51  __atomic_store_n(&s, 0, __ATOMIC_RELAXED);
52  sink = __atomic_load_n(&s, __ATOMIC_ACQUIRE);
53  global = 43;
54}
55
56int main() {
57  pthread_t t;
58  pthread_create(&t, 0, Thread, 0);
59  foobar();
60  barfoo();
61  pthread_join(t, 0);
62  if (sink != 0)
63    exit(1);
64  fprintf(stderr, "DONE\n");
65  return 0;
66}
67
68