Patchwork libgo patch committed: Fix use of __atomic_compare_exchange_n

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Submitter Ian Taylor
Date Nov. 17, 2012, 12:52 a.m.
Message ID <mcrhaopaw53.fsf@google.com>
Download mbox | patch
Permalink /patch/199809/
State New
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Comments

Ian Taylor - Nov. 17, 2012, 12:52 a.m.
Based on advice from Dmitry Vyukov, this patch fixes the use of
__atomic_compare_exchange_n in libgo.  The Go library assumes a strong
compare-exchange operation, and always assumes sequential consistency
around the operation.  Bootstrapped and ran Go testsuite on
x86_64-unknown-linux-gnu, where, as it happens, this patch makes no
different anyhow.  Committed to mainline.

Ian

Patch

diff -r db71d396d9e5 libgo/runtime/runtime.h
--- a/libgo/runtime/runtime.h	Fri Nov 16 08:03:04 2012 -0800
+++ b/libgo/runtime/runtime.h	Fri Nov 16 16:43:50 2012 -0800
@@ -518,7 +518,7 @@ 
 void	free(void *v);
 #define runtime_cas(pval, old, new) __sync_bool_compare_and_swap (pval, old, new)
 #define runtime_casp(pval, old, new) __sync_bool_compare_and_swap (pval, old, new)
-#define runtime_cas64(pval, pold, new) __atomic_compare_exchange_n (pval, pold, new, 1, __ATOMIC_SEQ_CST, __ATOMIC_RELAXED)
+#define runtime_cas64(pval, pold, new) __atomic_compare_exchange_n (pval, pold, new, 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)
 #define runtime_xadd(p, v) __sync_add_and_fetch (p, v)
 #define runtime_xadd64(p, v) __sync_add_and_fetch (p, v)
 #define runtime_xchg(p, v) __atomic_exchange_n (p, v, __ATOMIC_SEQ_CST)