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Fix build break around __atomic_*() with GCC<4.7

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The __atomic_* GCC primitives were introduced in GCC 4.7, but Red Hat
Enterprise Linux 6.x (for example) provides GCC 4.4. Tweak the current code to
use the (most conservative) __sync_synchronize() primitive provided by those
older GCC versions.

Fixes https://github.com/SELinuxProject/selinux/issues/97

(Really, no __atomic or __sync operations are needed here at all, since POSIX
4.12 "Memory Synchronization" says pthread_mutex_lock() and
pthread_mutex_unlock() "synchronize memory with respect to other threads"...)
This commit is contained in:
Hollis Blanchard 2018-08-13 12:42:14 -07:00 committed by Nicolas Iooss
parent 220a51b921
commit 70b9658d8c
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1 changed files with 18 additions and 0 deletions
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18
libselinux/src/label_file.h
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@ -351,8 +351,14 @@ static inline int compile_regex(struct saved_data *data, struct spec *spec,
* init_routine does not take a parameter, it's not possible
* to use, so we generate the same effect with atomics and a
* mutex */
#ifdef __ATOMIC_RELAXED
regex_compiled =
__atomic_load_n(&spec->regex_compiled, __ATOMIC_ACQUIRE);
#else
/* GCC <4.7 */
__sync_synchronize();
regex_compiled = spec->regex_compiled;
#endif
if (regex_compiled) {
return 0; /* already done */
}
@ -360,8 +366,14 @@ static inline int compile_regex(struct saved_data *data, struct spec *spec,
__pthread_mutex_lock(&spec->regex_lock);
/* Check if another thread compiled the regex while we waited
* on the mutex */
#ifdef __ATOMIC_RELAXED
regex_compiled =
__atomic_load_n(&spec->regex_compiled, __ATOMIC_ACQUIRE);
#else
/* GCC <4.7 */
__sync_synchronize();
regex_compiled = spec->regex_compiled;
#endif
if (regex_compiled) {
__pthread_mutex_unlock(&spec->regex_lock);
return 0;
@ -404,7 +416,13 @@ static inline int compile_regex(struct saved_data *data, struct spec *spec,
}
/* Done. */
#ifdef __ATOMIC_RELAXED
__atomic_store_n(&spec->regex_compiled, true, __ATOMIC_RELEASE);
#else
/* GCC <4.7 */
spec->regex_compiled = true;
__sync_synchronize();
#endif
__pthread_mutex_unlock(&spec->regex_lock);
return 0;
}