linux-kernel - Re: [tip:x86/asm] x86-64: Use normal ptregs stub for execve

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Message-ID: <73c1f2161001270721x3d07b507lb78fa8c53567dcaa@mail.gmail.com>
Date:	Wed, 27 Jan 2010 10:21:15 -0500
From:	Brian Gerst <brgerst@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/asm] x86-64: Use normal ptregs stub for execve

On Wed, Jan 27, 2010 at 8:07 AM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * tip-bot for Brian Gerst <brgerst@...il.com> wrote:
>
>> Commit-ID:  f19a25c872b20ae4357f72687cf3e7b0da220ee2
>> Gitweb:     http://git.kernel.org/tip/f19a25c872b20ae4357f72687cf3e7b0da220ee2
>> Author:     Brian Gerst <brgerst@...il.com>
>> AuthorDate: Mon, 25 Jan 2010 10:47:33 -0500
>> Committer:  H. Peter Anvin <hpa@...or.com>
>> CommitDate: Tue, 26 Jan 2010 23:38:14 -0800
>>
>> x86-64: Use normal ptregs stub for execve
>>
>> Execve historically passed regs by value, so it had a seperate stub.
>> This is no longer true, so change it to use a normal PTREGSCALL stub.
>>
>> Signed-off-by: Brian Gerst <brgerst@...il.com>
>> LKML-Reference: <1264434453-2204-1-git-send-email-brgerst@...il.com>
>> Signed-off-by: H. Peter Anvin <hpa@...or.com>
>> ---
>>  arch/x86/kernel/entry_64.S |   17 +----------------
>>  1 files changed, 1 insertions(+), 16 deletions(-)
>
> FYI, -tip testing found that this commit breaks the grub binary on 64-bit,
> simply running /sbin/grub causes it to segfault:
>
> [ 3145.999766] grub[6706] general protection ip:805c481 sp:ff95629c error:0 in
> grub[8048000+8c000]
>
> i've excluded this commit for now.
>
>        Ingo
>
>

I see what is going on.  Grub is a 32-bit statically linked executable
even on a 64-bit distro.  The old execve stub forced return to
userspace via iret, but PTREGSCALL apparently doesn't.  This means
that the 32-bit %cs isn't getting set.  Drop this patch for now.

--
Brian Gerst
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