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

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Message-ID: <4B799C3F.7010308@zytor.com>
Date:	Mon, 15 Feb 2010 11:10:55 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: x86: get rid of the insane TIF_ABI_PENDING bit

On 02/15/2010 08:17 AM, Oleg Nesterov wrote:
>> +
>> +	/* Prepare the first "return" to user space */
>> +	current_thread_info()->status |= TS_COMPAT;
> 
> Can't understand why we need TS_COMPAT. I assume this is correct,
> this was copied from flush_thread().
> 
> What TS_COMPAT actually means? I thought it just means "the task
> is inside 32-bit syscall".
> 
> If a 64bit task execs a 32bit app, can't this TS_COMPAT break, say,
> syscall_get_arguments() ?
> 
> Just curious, I don't really understand COMPAT issues anyway.
> 

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.

	-hpa

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

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