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| // RUN: %clang_tsan -O1 %s -o %t && %run %t 2>&1 | FileCheck %s
#include "test.h"
// Test case https://github.com/google/sanitizers/issues/494
// Tsan sees false HB edge on address pointed to by syncp variable.
// It is false because when acquire is done syncp points to a var in one frame,
// and during release it points to a var in a different frame.
// The code is somewhat tricky because it prevents compiler from optimizing
// our accesses away, structured to not introduce other data races and
// not introduce other synchronization, and to arrange the vars in different
// frames to occupy the same address.
// The data race CHECK-NOT below actually must be CHECK, because the program
// does contain the data race on global.
// CHECK-NOT: WARNING: ThreadSanitizer: data race
// CHECK: DONE
long global;
long *syncp;
long *addr;
long sink;
void *Thread(void *x) {
while (__atomic_load_n(&syncp, __ATOMIC_ACQUIRE) == 0)
usleep(1000); // spin wait
global = 42;
__atomic_store_n(syncp, 1, __ATOMIC_RELEASE);
__atomic_store_n(&syncp, 0, __ATOMIC_RELAXED);
return NULL;
}
void __attribute__((noinline)) foobar() {
__attribute__((aligned(64))) long s;
addr = &s;
__atomic_store_n(&s, 0, __ATOMIC_RELAXED);
__atomic_store_n(&syncp, &s, __ATOMIC_RELEASE);
while (__atomic_load_n(&syncp, __ATOMIC_RELAXED) != 0)
usleep(1000); // spin wait
}
void __attribute__((noinline)) barfoo() {
__attribute__((aligned(64))) long s;
if (addr != &s) {
printf("address mismatch addr=%p &s=%p\n", addr, &s);
exit(1);
}
__atomic_store_n(&addr, &s, __ATOMIC_RELAXED);
__atomic_store_n(&s, 0, __ATOMIC_RELAXED);
sink = __atomic_load_n(&s, __ATOMIC_ACQUIRE);
global = 43;
}
int main() {
pthread_t t;
pthread_create(&t, 0, Thread, 0);
foobar();
barfoo();
pthread_join(t, 0);
if (sink != 0)
exit(1);
fprintf(stderr, "DONE\n");
return 0;
}
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