linux-kernel - Re: x86: get rid of the insane TIF_ABI

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Date:	Mon, 15 Feb 2010 12:07:50 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Roland McGrath <roland@...hat.com>
CC:	Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: x86: get rid of the insane TIF_ABI_PENDING bit

On 02/15/2010 11:41 AM, Roland McGrath wrote:
>> I suspect the purpose of TS_COMPAT is actually so you can ptrace() the
>> newly exec'd process (and see it as a 32-bit process!) before it returns
>> to userspace.  The comment, obviously, is wrong -- that again refers to
>> TIF_IA32.
> 
> I don't follow you.  TS_COMPAT does not affect ptrace.
> It affects syscall-audit, but only at syscall entry time.
> It affects asm/syscall.h accessors, but ptrace does not use those.
> It affects whatever uses is_compat_task(), but I can't see anything
> where that matters except inside some particular syscall or for
> syscall restart after signals.
> 
> TS_COMPAT does not affect the syscall return machinery itself.
> The return path just follows from the particular entry path.

It's entirely possible it is completely superfluous.  The patch in
question only moves the setting.  I don't know what gdb or strace use to
distinguish a 32-bit and a 64-bit process, which is why I thought it
might have something to do with ptrace.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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