linux-kernel - Re: Compat 32-bit syscall entry from 64-bit task!?

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Date:	Wed, 18 Jan 2012 13:53:12 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Roland McGrath <mcgrathr@...gle.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Indan Zupancic <indan@....nu>,
	Andi Kleen <andi@...stfloor.org>,
	Jamie Lokier <jamie@...reable.org>,
	Andrew Lutomirski <luto@....edu>,
	Oleg Nesterov <oleg@...hat.com>,
	Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org,
	keescook@...omium.org, john.johansen@...onical.com,
	serge.hallyn@...onical.com, coreyb@...ux.vnet.ibm.com,
	pmoore@...hat.com, eparis@...hat.com, djm@...drot.org,
	segoon@...nwall.com, rostedt@...dmis.org, jmorris@...ei.org,
	scarybeasts@...il.com, avi@...hat.com, penberg@...helsinki.fi,
	viro@...iv.linux.org.uk, mingo@...e.hu, akpm@...ux-foundation.org,
	khilman@...com, borislav.petkov@....com, amwang@...hat.com,
	ak@...ux.intel.com, eric.dumazet@...il.com, gregkh@...e.de,
	dhowells@...hat.com, daniel.lezcano@...e.fr,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, olofj@...omium.org,
	mhalcrow@...gle.com, dlaor@...hat.com
Subject: Re: Compat 32-bit syscall entry from 64-bit task!?

On 01/18/2012 01:51 PM, Roland McGrath wrote:
> 
> There are all the concerns about obscure ABI compatibility with
> expectations of existing debuggers and so forth, which Linus has mentioned.
> For that I can accept his point that things today so mishandle the
> int80-from-64 case that something like a new meaning for high bits of
> orig_ax or whatnot in just that case would not be actually problematic.
> When you and I were discussing a more general feature of distinguishing
> int80 from sysenter from syscall from traps from asynchronous interrupts,
> that was of more concern.
> 
> I do feel strongly that any new means of exposing bona fide user state
> ought to be done via the user_regset mechanism.  (i.e., either overloading
> some existing user_regs_struct bits if that truly is harmless to
> compatibility, or adding a new regset flavor.)  That way it is
> automatically recorded in core files, accessible with PTRACE_GETREGSET,
> etc.  (But I'm not really working on this stuff any more, so I'm out of the
> business of arguing strenuously about such opinions.)
> 

I think we can obviously agree that regsets is the only way to go for
any kind of new state.

	-hpa

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