Re: [PATCH] MdePkg/Include: AARCH64: disable outline atomics on GCC 10.2+

["Laszlo Ersek" <lersek@redhat.com>]

On 05/22/20 12:12, Ard Biesheuvel wrote:
> GCC 10 enabled a feature by default that was introduced in GCC 9,
> which results in atomic operations to be emitted as function calls
> to intrinsics provided by a runtime library.
> 
> Atomics are hardly used in EDK2, which runs on a single CPU anyway,
> and any benefit that would result from reusing library code that
> implements these operations is defeated by the fact that every EDK2
> module will need to have its own copy anyway.
> 
> So let's disable this feature on GCC versions that support the
> pragma to do so (GCC 10.2 and up)
> 
> Link: https://bugzilla.tianocore.org/show_bug.cgi?id=2723
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
> ---
> The GCC support for this pragma has already been pulled into the 10.2
> release branch. I think we should consider adding this to the stable
> tag, so that the issue can easily be resolved by upgrading the compiler.
> Whether we add the intrinsics too is a separate matter, but we can
> revisit that later.
> 
>  MdePkg/Include/AArch64/ProcessorBind.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/MdePkg/Include/AArch64/ProcessorBind.h b/MdePkg/Include/AArch64/ProcessorBind.h
> index 896bf273ac7a..a3ca8f09e51c 100644
> --- a/MdePkg/Include/AArch64/ProcessorBind.h
> +++ b/MdePkg/Include/AArch64/ProcessorBind.h
> @@ -24,6 +24,17 @@
>  #pragma pack()
>  #endif
>  
> +#if defined(__GNUC__) && !defined(__clang__)
> +
> +//
> +// Disable GCC outline atomics
> +// Link: https://bugzilla.tianocore.org/show_bug.cgi?id=2723
> +//
> +#if __GNUC__ > 10 || (__GNUC__ == 10 && __GNUC_MINOR__ >= 2)
> +#pragma GCC target "no-outline-atomics"
> +#endif
> +#endif
> +
>  #if defined(_MSC_EXTENSIONS)
>  
>  //
> 

Reviewed-by: Laszlo Ersek <lersek@redhat.com>

But I think it should be merged later, after GCC 10.2 is out.

(Obviously I don't "insist" that we follow this approach, I'm just OK
with it.)

Thanks
Laszlo