linux-kernel - Re: arch/x86/include/asm/cmpxchg_32.h:149:9: error: inline assembly requires more registers than available

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Date: Mon, 24 Jun 2024 10:17:50 -0400
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Uros Bizjak <ubizjak@...il.com>
Cc: kernel test robot <lkp@...el.com>, oe-kbuild-all@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>, 
	Borislav Petkov <bp@...en8.de>, Peter Zijlstra <peterz@...radead.org>
Subject: Re: arch/x86/include/asm/cmpxchg_32.h:149:9: error: inline assembly
 requires more registers than available

On Mon, 24 Jun 2024 at 09:59, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Mon, 24 Jun 2024 at 03:36, Uros Bizjak <ubizjak@...il.com> wrote:
> >
> > A real fix, not only a workaround, is to rewrite asm arguments to
> > something like (untested, but "should work"TM):
>
> Sadly, I already tried that, and it didn't help.

Bah. I _had_ tried that, but I had tried it on __arch_cmpxchg64_emu(),
not on the "try" version.

And no, it hadn't helped.

But doing it *right*, and also doing __arch_try_cmpxchg64_emu() *does*
actually help.

Well, at least the attached patch compiles with the bad config and clang.

I'm not certain it does the right thing, because I did more than just
the %esi games to try to simplify it.

It's *ENTIRELY* possible that I screwed up. Just in this thread, I
have looked at the wrong inline asm at least twice now, so I'm not
feeling super-competent right now.

I'm sending the patch out in the hope that another set of eyes will
make it actually better.

            Linus

View attachment "patch.diff" of type "text/x-patch" (2244 bytes)