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

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Date:	Mon, 15 Feb 2010 08:23:19 -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:
> 
>> +void set_personality_ia32(void)
>> +{
>> +	/* inherit personality from parent */
>> +
>> +	/* Make sure to be in 32bit mode */
>> +	set_thread_flag(TIF_IA32);
>> +
>> +	/* 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".

Yes.  In this case, though, it was a 64-bit syscall when the process did
the exec, but it needs to "return" as if it came from a 32-bit syscall;
that's why we set the TS_COMPAT bit.

> If a 64bit task execs a 32bit app, can't this TS_COMPAT break, say,
> syscall_get_arguments() ?
> 

At that point (this is after the exec!) we don't get arguments anyway.

> Just curious, I don't really understand COMPAT issues anyway.

	-hpa

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

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