Re: [PATCH] Fix ARM64/MSVC atomic memory ordering issues on Win11 by adding explicit DMB ​barriers

Hi,

On 2025-11-22 16:43:30 -0500, Greg Burd wrote:
> With the new MSVC compiler flag Andres mentioned (/arch:armv9.4) I only
> had to update the S_UNLOCK() macro, the compiler did the rest correctly
> AFAICT.

Just to be clear - the flag shouldn't be necessary for things to work
correctly. I was only using it to have godbolt inline the intrinsics, rather
than have them generate an out-of-line function call that I couldn't easily
inspect. I'm fairly sure that the out-of-line functions also have the relevant
barriers.


> @@ -2509,7 +2513,10 @@ int main(void)
>  }
>  '''
>  
> -  if cc.links(prog, name: '__crc32cb, __crc32ch, __crc32cw, and __crc32cd without -march=armv8-a+crc',
> +  if cc.get_id() == 'msvc'
> +    cdata.set('USE_ARMV8_CRC32C', 1)
> +    have_optimized_crc = true

Should have a comment explaining why we can do this unconditionally...


Greetings,

Andres Freund