Re: [edk2-devel] [PATCH] MdePkg/Include: AARCH64: disable outline atomics on GCC 10.2+

["Leif Lindholm" <leif@nuviainc.com>]

On Sat, May 23, 2020 at 00:09:52 +0200, Ard Biesheuvel wrote:
> > > > 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.)
> > 
> > Oh and I think both this patch and the assembly language implementation
> > for the atomics should be delayed after the stable tag. gcc-10 is a new
> > toolchain; so even if we don't introduce a new toolchain tag such as
> > GCC10 for it, whatever we do in order to make it work, that's feature
> > enablement in my book.
> 
> Works for me. By the time the next stable tag comes around, early adopters
> that are now on GCC 10.1 will likely have moved to 10.2 by that time, and so
> we may not need the assembly patch at all.

I'm not ecstatic that we'll be releasing the first stable tag known to
break with current toolchains.

This isn't just affecting random crazies pulling latest toolchains
down, but people using their distro defaults (native or cross).
I don't recall if 10.1 ended up being default in F32, but it was
definitely included. In Arch, it does appear default.

Debian/Ubuntu are unaffected in their stable releases.

I agree it's a transitional issue, but I would really prefer to have
the intrinsics included in the release.

/
    Leif