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From: David Laight <David.Laight@ACULAB.COM>
To: 'Linus Torvalds' <torvalds@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>
Cc: Andrew Cooper <Andrew.Cooper3@citrix.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Bill Wendling <morbo@google.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, Nathan Chancellor <nathan@kernel.org>,
	"Juergen Gross" <jgross@suse.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"llvm@lists.linux.dev" <llvm@lists.linux.dev>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-toolchains <linux-toolchains@vger.kernel.org>
Subject: RE: [PATCH v5] x86: use builtins to read eflags
Date: Fri, 18 Mar 2022 22:43:13 +0000	[thread overview]
Message-ID: <5794cceec50a4f1ebca069d5a31afcdf@AcuMS.aculab.com> (raw)
In-Reply-To: <CAHk-=wj1Z_zzY7ADxaarorK5sh2xkwbcHxJTzW=bsYChWJGBGg@mail.gmail.com>

From: Linus Torvalds
> Sent: 18 March 2022 18:19
> 
> On Fri, Mar 18, 2022 at 10:59 AM Andy Lutomirski <luto@kernel.org> wrote:
> >
> > I generally agree.  In this particular case, though, I will keep using
> > the builtin in tools/testing/selftests/x86/helpers.h unless we actually
> > hit breakage.  This is because this is *user* code, it is compiled with
> > the redzone enabled, and the asm code to do the right thing when the
> > redzone is enabled is too hairy for me to want to deal with it.
> 
> Yeah, redzoning is a problem for "pushf".
> 
> Or rather, it's not the redzoning itself, but the fact that the
> compiler might use the word under the stack for random other things,
> and the pushf will then corrupt some local variable storage.
> 
> I think it would be lovely to solve that in inline asm itself some way
> - by marking the stack pointer clobbered or something.

Something that generates:
	mov	%rax,-8(%rsp)
	pushf
	xchg	%rax,0(%rsp)
	add	%rsp,8
should work with or without a redzone.
Will be a bit slower :-(

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

  parent reply	other threads:[~2022-03-18 22:43 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-15 21:18 [PATCH] x86: use builtins to read eflags Bill Wendling
2021-12-15 22:46 ` Nathan Chancellor
2021-12-15 23:26 ` Peter Zijlstra
2021-12-16 20:00   ` Bill Wendling
2021-12-16 20:07     ` Nick Desaulniers
2021-12-16  0:57 ` Thomas Gleixner
2021-12-16 19:55   ` Bill Wendling
2021-12-17 12:48     ` Peter Zijlstra
2021-12-17 19:39     ` Thomas Gleixner
2022-03-14 23:09     ` H. Peter Anvin
2022-03-15  0:08       ` Bill Wendling
2021-12-16 19:58   ` Nick Desaulniers
2021-12-29  2:12 ` [PATCH v2] " Bill Wendling
2022-01-27 20:56   ` Bill Wendling
2022-02-04  0:16   ` Thomas Gleixner
2022-02-04  0:58     ` Bill Wendling
2022-02-04  0:57   ` [PATCH v3] " Bill Wendling
2022-02-07 22:11     ` Nick Desaulniers
2022-02-08  9:14       ` David Laight
2022-02-08 23:18         ` Bill Wendling
2022-02-14 23:53         ` Nick Desaulniers
2022-02-10 22:31     ` [PATCH v4] " Bill Wendling
2022-02-11 16:40       ` David Laight
2022-02-11 19:25         ` Bill Wendling
2022-02-11 22:09           ` David Laight
2022-02-11 23:33             ` Bill Wendling
2022-02-12  0:24           ` Nick Desaulniers
2022-02-12  9:23             ` Bill Wendling
2022-02-15  0:33               ` Nick Desaulniers
2022-03-01 20:19       ` [PATCH v5] " Bill Wendling
2022-03-14 23:07         ` Bill Wendling
     [not found]           ` <AC3D873E-A28B-41F1-8BF4-2F6F37BCEEB4@zytor.com>
2022-03-15  7:19             ` Bill Wendling
2022-03-17 15:43               ` H. Peter Anvin
2022-03-17 18:00                 ` Nick Desaulniers
2022-03-17 18:52                   ` Linus Torvalds
2022-03-17 19:45                     ` Bill Wendling
2022-03-17 20:13                       ` Linus Torvalds
2022-03-17 21:10                         ` Bill Wendling
2022-03-17 21:21                           ` Linus Torvalds
2022-03-17 21:45                             ` Bill Wendling
2022-03-17 22:51                               ` Linus Torvalds
2022-03-17 23:14                                 ` Linus Torvalds
2022-03-17 23:19                                 ` Segher Boessenkool
2022-03-17 23:31                                   ` Linus Torvalds
2022-03-18  0:05                                     ` Segher Boessenkool
2022-03-17 22:37                       ` Segher Boessenkool
2022-03-17 20:13                     ` Florian Weimer
2022-03-17 20:36                       ` Linus Torvalds
2022-03-18  0:25                         ` Segher Boessenkool
2022-03-18  1:21                           ` Linus Torvalds
2022-03-18  1:50                             ` Linus Torvalds
2022-03-17 21:05                     ` Andrew Cooper
2022-03-17 21:39                       ` Linus Torvalds
2022-03-18 17:59                         ` Andy Lutomirski
2022-03-18 18:19                           ` Linus Torvalds
2022-03-18 21:48                             ` Andrew Cooper
2022-03-18 23:10                               ` Linus Torvalds
2022-03-18 23:42                                 ` Segher Boessenkool
2022-03-19  1:13                                   ` Linus Torvalds
2022-03-19 23:15                                   ` Andy Lutomirski
2022-03-18 22:09                             ` Segher Boessenkool
2022-03-18 22:33                               ` H. Peter Anvin
2022-03-18 22:36                               ` David Laight
2022-03-18 22:47                                 ` H. Peter Anvin
2022-03-18 22:43                             ` David Laight [this message]
2022-03-18 23:03                               ` H. Peter Anvin
2022-03-18 23:04                         ` Segher Boessenkool
2022-03-18 23:52                           ` David Laight

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