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Re: [tsan] Instrument atomics
On Tue, Nov 27, 2012 at 12:47 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
> On Tue, Nov 27, 2012 at 12:23 PM, Jakub Jelinek <jakub@redhat.com> wrote:
>> On Tue, Nov 27, 2012 at 12:13:42PM +0400, Dmitry Vyukov wrote:
>>> I've added 128-bit atomic ops:
>>> http://llvm.org/viewvc/llvm-project?view=rev&revision=168683
>>
>> Thanks.
>>>
>>> Refactored atomic ops so that the atomic operation itself is done
>>> under the mutex:
>>> http://llvm.org/viewvc/llvm-project?view=rev&revision=168682
>>
>> This is IMHO very wrong. It is fine if you hold some mutex over the atomic
>> operation, but you do need to perform the operation atomicly, e.g. you can't
>> rely that all atomic accesses to that memory location are performed from
>> -fsanitize=thread compiled code (it could be from non-instrumented code
>> from e.g. other libraries, could be from user written assembly, etc.).
>> By not doing the operation atomicly, the other code might observe
>> inconsistent state, or the tsan non-atomic code might be doing the wrong
>> thing. One thing is that the tsan analysis will be right, but another
>> thing is that the program itself might misbehave.
>
>
> Yes, you are right.
> I think I've done them atomically initially because of things like
> FUTEX_WAKE_OP. I will fix that.
>
>
>>> And added atomic nand operation:
>>> http://llvm.org/viewvc/llvm-project?view=rev&revision=168584
>>
>> Thanks. Can you please also add the memory range read/write functions?
>> That could be used both for builtins (e.g. if user writes
>> __builtin_memcpy (&a, &b, sizeof (a));
>> in his code, no -fno-builtin or similar actually disables that), compiler
>> generated builtins - e.g. structure copies
>> struct large a, b;
>> ...
>> a = b;
>> and also for accesses of sizes that aren't supported by the library
>> (consider 32-byte or 64-byte vectors etc.).
>
> Done:
> http://llvm.org/viewvc/llvm-project?view=rev&revision=168692
Kostya is going to do gcc<->llvm library sync today.