Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.18-1 tag

From: Segher Boessenkool <segher@kernel.crashing.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Michal Suchánek" <msuchanek@suse.de>,
	"Paul Menzel" <pmenzel@molgen.mpg.de>,
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	"Linus Torvalds" <torvalds@linux-foundation.org>,
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Subject: Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.18-1 tag
Date: Wed, 30 Mar 2022 12:07:06 -0500	[thread overview]
Message-ID: <20220330170706.GV614@gate.crashing.org> (raw)
In-Reply-To: <87k0cbfuf4.fsf@mpe.ellerman.id.au>

On Thu, Mar 31, 2022 at 12:21:03AM +1100, Michael Ellerman wrote:
> Michal Suchánek <msuchanek@suse.de> writes:
> > On Mon, Mar 28, 2022 at 08:07:13PM +1100, Michael Ellerman wrote:
> >> Linus Torvalds <torvalds@linux-foundation.org> writes:
> >> > On Fri, Mar 25, 2022 at 3:25 AM Michael Ellerman <mpe@ellerman.id.au> wrote:
> >> 
> >> > That said:
> >> >
> >> >> There's a series of commits cleaning up function descriptor handling,
> >> >
> >> > For some reason I also thought that powerpc had actually moved away
> >> > from function descriptors, so I'm clearly not keeping up with the
> >> > times.
> >> 
> >> No you're right, we have moved away from them, but not entirely.
> >> 
> >> Functions descriptors are still used for 64-bit big endian, but they're
> >> not used for 64-bit little endian, or 32-bit.
> >
> > There was a patch to use ABIv2 for ppc64 big endian. I suppose that
> > would rid usof the gunction descriptors for good.
> 
> It would be nice.
> 
> The hesitation in the past was that the GNU toolchain developers don't
> officially support BE+ELFv2, though it is in use so it does work.

We do not officially support ELFv2 BE because there are no significant
users, so we cannot have the same confidence it works correctly.

It isn't tested often with GCC for example, mainly because it isn't
convenient to do without pre-packaged user space for it (and on the
other hand, there isn't much demand for it).

> > Maybe it's worth resurrecting?
> 
> Yeah maybe we should think about it again. If it builds with clang/lld
> that would be a real plus.

With GCC it should work fine still.  But no doubt you will find some
edge cases...  which you won't find until you try :-)

Segher