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

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Message-ID: <20100215165012.GA20447@redhat.com>
Date:	Mon, 15 Feb 2010 17:50:12 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.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, H. Peter Anvin wrote:
>
> 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;

Could you please point me where do we check TS_COMPAT during return
to user-mode?

> > 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.

I meant /proc/pid/syscall, but even if I am right this probably
doesn't matter.

Oleg.

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