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

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Message-Id: <20100215211457.C2E143E8@magilla.sf.frob.com>
Date:	Mon, 15 Feb 2010 13:14:57 -0800 (PST)
From:	Roland McGrath <roland@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.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

> 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.

Well, whatever it that might be, they have no way to know about the
TS_COMPAT setting.  TS_COMPAT affects three things: audit_syscall_entry()
parameters, asm/syscall.h stuff, and is_compat_task()--nothing that is
directly visible from userland unless you count /proc/pid/syscall values.
Notably, that includes syscall_get_error() that is used in signal recovery.

AFAICT the only interesting use of is_compat_task() is the drivers/input stuff.

Thanks,
Roland
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