[edk2-devel] [PATCH v2] ArmPkg/CompilerIntrinsicsLib: provide atomics intrinsics

[Ard Biesheuvel]

On 5/21/20 3:16 PM, Leif Lindholm wrote:
> On Thu, May 21, 2020 at 14:58:56 +0200, Ard Biesheuvel wrote:
>>> Reviewed-by: Leif Lindholm <leif at nuviainc.com>
>>> Thanks!
>>>
>>
>> Apparently, GCC 10 is getting fixed so that we can set a #pragma in
>> MdePkg/Include/AArch64/ProcessorBind.h, and be done with it.
>>
>> That does mean you would need GCC 10.2 at least, or you get the error,
>> unless we merge this patch as well. That would mean the intrinsics are never
>> used in practice, but using a compiler that does use them will not break the
>> build.
>>
>> I am leaning towards omitting this patch, but I could be convinced to adopt
>> both mitigations. But the #pragma is strongly preferred.
> 
> What is the codesize impact on a full RELEASE image?

Not sure how that matters? Given the modular nature of EDK2, I would not 
expect the outline atomics to have any measurable size benefit. The 
intrinsics library is static, with each of the 100 different functions 
emitted into a separate section, so you only get what you use.

> If non-negligable, how about #ifdefing the whole content out unless
> some specific preprocessor flag is passed? Then at least there's a
> quick workaround for anyone who needs it.
> 

The linker will only incorporate the parts that are actually used.

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