linux-kernel - RE: remove the last set_fs() in common code, and remove it for x86 and powerpc v3

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Date:   Thu, 10 Sep 2020 08:04:19 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Linus Torvalds' <torvalds@...ux-foundation.org>,
        Segher Boessenkool <segher@...nel.crashing.org>
CC:     Al Viro <viro@...iv.linux.org.uk>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Christoph Hellwig <hch@....de>
Subject: RE: remove the last set_fs() in common code, and remove it for x86
 and powerpc v3

From: Linus Torvalds
> Sent: 09 September 2020 22:34
> On Wed, Sep 9, 2020 at 11:42 AM Segher Boessenkool
> <segher@...nel.crashing.org> wrote:
> >
> > It will not work like this in GCC, no.  The LLVM people know about that.
> > I do not know why they insist on pushing this, being incompatible and
> > everything.
> 
> Umm. Since they'd be the ones supporting this, *gcc* would be the
> incompatible one, not clang.

I had an 'interesting' idea.

Can you use a local asm register variable as an input and output to
an 'asm volatile goto' statement?

Well you can - but is it guaranteed to work :-)

	David

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