[PATCH] D118024: [sanitizer_common] Use atomic builtin in sanitizer_atomic_clang.h

[Rainer Orth via Phabricator via llvm-commits]

ro added inline comments.


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Comment at: compiler-rt/lib/sanitizer_common/sanitizer_atomic_clang.h:78
+  return __atomic_compare_exchange(&a->val_dont_use, cmp, &xchg, false, mo,
+                                   __ATOMIC_RELAXED);
 }
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efriedma wrote:
> Please don't change the memory ordering in this patch.  (__sync_* is sequentially consistent.)  If you really want to change it, please post as a separate patch with an appropriate title.
It wasn't clear to me from GCC's `__sync` builtin documentation that they are `__ATOMIC_SEQ_CST`.  I just assumed that `scudo/standalone/atomic_helpers.h` really implemented `atomic_compare_exchange_strong`.

As I mentioned, both `__ATOMIC_RELAXED` and `__ATOMIC_SEQ_CST` cause 3 regressions on Solaris/sparcv9, so this patch certainly cannot go in as is, despite fixing hundreds of link failures.


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Comment at: compiler-rt/lib/sanitizer_common/sanitizer_atomic_clang.h:94
 // proceed the template definitions above.
 #if defined(_MIPS_SIM) && defined(_ABIO32)
   #include "sanitizer_atomic_clang_mips.h"
----------------
efriedma wrote:
> Have you looked at extending this code to SPARC?  I'm a little concerned that the dependency on libatomic might cause issues (however we write it).
Not yet: I'd hoped to be able to come up with a minimal workaround for LLVM not fully implementing atomics on SPARC v8+ (or even better, fix that problem instead).

Switching from `__sync_val_compare_and_swap` to `__atomic_compare_exchange` shouldn't make a difference for any target inlining atomics IIUC.  Those that don't would just trade link failures for one function for another.


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  https://reviews.llvm.org/D118024/new/

https://reviews.llvm.org/D118024