linux-kernel - Re: [PATCH] pop previous section in alternative.c

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Message-ID: <Pine.LNX.4.58.0804101219170.7952@gandalf.stny.rr.com>
Date:	Thu, 10 Apr 2008 12:20:31 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Andy Whitcroft <apw@...dowen.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	akpm@...ux-foundation.org, Rusty Russell <rusty@...tcorp.com.au>,
	Glauber de Oliveira Costa <gcosta@...hat.com>,
	Jan Beulich <jbeulich@...ell.com>,
	Thomas Gleixner <tglx@...utronix.de>, pinskia@....gnu.org
Subject: Re: [PATCH] pop previous section in alternative.c



On Thu, 10 Apr 2008, H. Peter Anvin wrote:

> Linus Torvalds wrote:
> >
> > That would mark gcc itself as buggy, because gcc will move some things
> > into the #APP/#NO_APP thing, and sometimes doesn't end the #APP at all!
> >
>
> That is quite buggy indeed, since the whole #APP and #NO_APP string set
> are arbitrary strings that are part of the gcc configuration, marked as
> "what to insert before user assembly" and "what to insert after user
> assembly."  They are not guaranteed to be simple comments, in fact.
>
> In fact, gas *is* sensitive to #APP ... #NO_APP, so they are not simple
> comments.

Looking at the output below, shows that testing .sections in between
#APP and #NO_APP would in fact catch this bug.

-- Steve

.Ltext0:
#APP
                .section .rodata, "a"
intelnops: .byte 0x90
.byte 0x89,0xf6
.byte 0x8d,0x76,0x00
.byte 0x8d,0x74,0x26,0x00
.byte 0x90
.byte 0x8d,0x74,0x26,0x00
.byte 0x8d,0xb6,0x00,0x00,0x00,0x00
.byte 0x8d,0xb4,0x26,0x00,0x00,0x00,0x00
.byte 0x90
.byte 0x8d,0xb4,0x26,0x00,0x00,0x00,0x00

                .section .rodata, "a"
k8nops: .byte 0x90
.byte 0x66,0x90
.byte 0x66,0x66,0x90
.byte 0x66,0x66,0x66,0x90
.byte 0x66,0x66,0x90
.byte 0x66,0x90
.byte 0x66,0x66,0x90
.byte 0x66,0x66,0x90
.byte 0x66,0x66,0x66,0x90
.byte 0x66,0x66,0x90
.byte 0x66,0x66,0x66,0x90
.byte 0x66,0x66,0x66,0x90

                .section .rodata, "a"
k7nops: .byte 0x90
.byte 0x8b,0xc0
.byte 0x8d,0x04,0x20
.byte 0x8d,0x44,0x20,0x00
.byte 0x8d,0x44,0x20,0x00
.byte 0x90
.byte 0x8d,0x80,0,0,0,0
.byte 0x8D,0x04,0x05,0,0,0,0
.byte 0x8D,0x04,0x05,0,0,0,0
.byte 0x90

                .section .rodata, "a"
p6nops: .byte 0x90
.byte 0x66,0x90
.byte 0x0f,0x1f,0x00
.byte 0x0f,0x1f,0x40,0
.byte 0x0f,0x1f,0x44,0x00,0
.byte 0x66,0x0f,0x1f,0x44,0x00,0
.byte 0x0f,0x1f,0x80,0,0,0,0
.byte 0x0f,0x1f,0x84,0x00,0,0,0,0

#NO_APP
        .type   constant_test_bit, @function
constant_test_bit:
.LFB30:

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