From: David Laight <David.Laight@ACULAB.COM>
To: 'Christophe Leroy' <christophe.leroy@csgroup.eu>,
'Linus Torvalds' <torvalds@linux-foundation.org>,
Segher Boessenkool <segher@kernel.crashing.org>
Cc: linux-arch <linux-arch@vger.kernel.org>,
Kees Cook <keescook@chromium.org>,
the arch/x86 maintainers <x86@kernel.org>,
"Nick Desaulniers" <ndesaulniers@google.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Christoph Hellwig <hch@lst.de>,
"Luis Chamberlain" <mcgrof@kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Alexey Dobriyan <adobriyan@gmail.com>
Subject: RE: remove the last set_fs() in common code, and remove it for x86 and powerpc v3
Date: Thu, 10 Sep 2020 09:26:28 +0000 [thread overview]
Message-ID: <59a64e9a210847b59f70f9bd2d02b5c3@AcuMS.aculab.com> (raw)
In-Reply-To: <186a62fc-042c-d6ab-e7dc-e61b18945498@csgroup.eu>
From: Christophe Leroy
> Sent: 10 September 2020 09:14
>
> Le 10/09/2020 à 10:04, David Laight a écrit :
> > From: Linus Torvalds
> >> Sent: 09 September 2020 22:34
> >> On Wed, Sep 9, 2020 at 11:42 AM Segher Boessenkool
> >> <segher@kernel.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 :-)
> >
>
> With gcc at least it should work according to
> https://gcc.gnu.org/onlinedocs/gcc/Local-Register-Variables.html
>
> They even explicitely tell: "The only supported use for this feature is
> to specify registers for input and output operands when calling Extended
> asm "
A quick test isn't good....
int bar(char *z)
{
__label__ label;
register int eax asm ("eax") = 6;
asm volatile goto (" mov $1, %%eax" ::: "eax" : label);
label:
return eax;
}
0000000000000040 <bar>:
40: b8 01 00 00 00 mov $0x1,%eax
45: b8 06 00 00 00 mov $0x6,%eax
4a: c3 retq
although adding:
asm volatile ("" : "+r" (eax));
either side of the 'asm volatile goto' does fix it.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2020-09-10 9:28 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-03 14:22 remove the last set_fs() in common code, and remove it for x86 and powerpc v3 Christoph Hellwig
2020-09-03 14:22 ` [PATCH 01/14] proc: remove a level of indentation in proc_get_inode Christoph Hellwig
2020-09-03 14:22 ` [PATCH 02/14] proc: cleanup the compat vs no compat file ops Christoph Hellwig
2020-09-03 14:22 ` [PATCH 03/14] proc: add a read_iter method to proc proc_ops Christoph Hellwig
2020-09-03 14:22 ` [PATCH 04/14] sysctl: Convert to iter interfaces Christoph Hellwig
2020-09-03 14:22 ` [PATCH 05/14] fs: don't allow kernel reads and writes without iter ops Christoph Hellwig
2020-10-01 22:38 ` Eric Biggers
2020-10-01 22:40 ` Al Viro
2020-10-02 16:27 ` Linus Torvalds
2020-10-09 22:06 ` Eric Biggers
2020-10-10 1:03 ` Linus Torvalds
2020-10-10 1:19 ` Eric Biggers
2020-10-10 1:29 ` Linus Torvalds
2020-10-10 1:55 ` Alexander Viro
2020-10-14 5:51 ` Christoph Hellwig
2020-09-03 14:22 ` [PATCH 06/14] fs: don't allow splice read/write without explicit ops Christoph Hellwig
2020-09-03 14:22 ` [PATCH 07/14] uaccess: add infrastructure for kernel builds with set_fs() Christoph Hellwig
2020-09-03 14:22 ` [PATCH 08/14] test_bitmap: remove user bitmap tests Christoph Hellwig
2020-09-03 14:22 ` [PATCH 09/14] lkdtm: remove set_fs-based tests Christoph Hellwig
2020-09-03 14:22 ` [PATCH 10/14] x86: move PAGE_OFFSET, TASK_SIZE & friends to page_{32,64}_types.h Christoph Hellwig
2020-09-03 14:22 ` [PATCH 11/14] x86: make TASK_SIZE_MAX usable from assembly code Christoph Hellwig
2020-09-03 14:22 ` [PATCH 12/14] x86: remove address space overrides using set_fs() Christoph Hellwig
2020-09-03 21:30 ` David Laight
2020-09-03 23:25 ` Linus Torvalds
2020-09-04 7:59 ` David Laight
2020-09-04 2:55 ` Al Viro
2020-09-04 4:41 ` Al Viro
2020-09-04 6:38 ` Christoph Hellwig
2020-09-04 7:47 ` Christoph Hellwig
2020-09-03 14:22 ` [PATCH 13/14] powerpc: use non-set_fs based maccess routines Christoph Hellwig
2020-09-03 14:22 ` [PATCH 14/14] powerpc: remove address space overrides using set_fs() Christoph Hellwig
2020-09-03 15:43 ` Christophe Leroy
2020-09-03 15:49 ` Christoph Hellwig
2020-09-03 15:56 ` Christoph Hellwig
2020-09-03 16:03 ` Christophe Leroy
2020-09-03 14:28 ` remove the last set_fs() in common code, and remove it for x86 and powerpc v3 Al Viro
2020-09-03 14:30 ` Christoph Hellwig
2020-09-03 14:36 ` Al Viro
2020-09-03 14:40 ` Christoph Hellwig
2020-09-09 17:31 ` Linus Torvalds
2020-09-09 18:40 ` Segher Boessenkool
2020-09-09 21:33 ` Linus Torvalds
2020-09-10 8:04 ` David Laight
2020-09-10 8:13 ` Christophe Leroy
2020-09-10 9:26 ` David Laight [this message]
2020-09-10 12:26 ` David Laight
2020-09-10 15:20 ` Segher Boessenkool
2020-09-10 15:31 ` David Laight
2020-09-10 17:15 ` Segher Boessenkool
2020-09-10 15:16 ` Segher Boessenkool
2020-09-10 15:44 ` Segher Boessenkool
2020-09-03 15:49 ` Linus Torvalds
2020-09-04 6:00 ` Ingo Molnar
2020-09-04 17:58 ` Alexey Dobriyan
2020-09-04 18:42 ` Linus Torvalds
2020-09-04 21:01 ` David Laight
2020-09-05 7:16 ` Christophe Leroy
2020-09-05 10:13 ` David Laight
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