[sanitizer] Fix sem_init_glibc.cc test on __HAVE_64B_ATOMIC arches.

[• koriakin]

Summary

Starting with 2.21, glibc can use one of 2 layouts for semaphores:
architectures that don't HAVE_64B_ATOMIC use an uint32_t field
with semaphore value, then a private field, then a waiting thread
count field - this is the layout currently assumed by the test.
However, HAVE_64B_ATOMIC arches use a fused uint64_t field that
contains the value in low bits and waiting thread count in high bits,
followed by a private field.

This resulted in taking private field from the wrong offset on 64-bit
atomic platforms (the test still passed, but didn't actually test
the private field). On big-endian platforms, this resulted in a fail,
since the first 4 bytes overlay the thread count field, and not
the value field.

Found while porting ASan to s390x.

[eugenis]

LGTM

[• koriakin]

Thanks. I don't have SVN write access, could you commit it for me?

[eugenis]

This breaks linux/x86_64 with
sem_init_glibc.cc:36: int main(): Assertion `a == 42' failed.

Failing Tests (4):

SanitizerCommon-asan-x86_64-Linux :: Linux/sem_init_glibc.cc
SanitizerCommon-lsan-x86_64-Linux :: Linux/sem_init_glibc.cc
SanitizerCommon-msan-x86_64-Linux :: Linux/sem_init_glibc.cc
SanitizerCommon-tsan-x86_64-Linux :: Linux/sem_init_glibc.cc

[• koriakin]

Whoops, it seems the new layout is only used in glibc >= 2.21. I assume you've tested on an older glibc?

I've added a __GLIBC_PREREQ test for that. In theory, we should be using the runtime version of the library, and not the version of headers, but it shouldn't matter since the program is compiled immediately before use. What do you think?

[eugenis]

Yes, I've got glibc 2.19.
I think this is fine in a test.

[eugenis]

r265715

test/sanitizer_common/TestCases/Linux/sem_init_glibc.cc

 // This test depends on the glibc layout of struct sem_t and checks that we
 // don't leave sem_t::private uninitialized.
 // UNSUPPORTED: android
+#include <features.h>
 #include <assert.h>
 #include <semaphore.h>
 #include <string.h>
+#include <stdint.h>
 
-void my_sem_init(bool priv, int value, unsigned *a, unsigned char *b) {
+// This condition needs to correspond to __HAVE_64B_ATOMICS macro in glibc.
+#if (defined(__x86_64__) || defined(__aarch64__) || defined(__powerpc64__) || \
+     defined(__s390x__) || defined(__sparc64__) || defined(__alpha__) || \
+     defined(__ia64__) || defined(__m68k__)) && __GLIBC_PREREQ(2, 21)
+typedef uint64_t semval_t;
+#else
+typedef unsigned semval_t;
+#endif
+
+void my_sem_init(bool priv, int value, semval_t *a, unsigned char *b) {
   sem_t sem;
   memset(&sem, 0xAB, sizeof(sem));
   sem_init(&sem, priv, value);
 
   char *p = (char *)&sem;
-  memcpy(a, p, sizeof(unsigned));
-  memcpy(b, p + sizeof(unsigned), sizeof(char));
+  memcpy(a, p, sizeof(semval_t));
+  memcpy(b, p + sizeof(semval_t), sizeof(char));
 
   sem_destroy(&sem);
 }
 
 int main() {
-  unsigned a;
+  semval_t a;
   unsigned char b;
 
   my_sem_init(false, 42, &a, &b);