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

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Message-ID: <4F30387A.9040209@zytor.com>
Date:	Mon, 06 Feb 2012 12:30:50 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Roland McGrath <mcgrathr@...gle.com>
CC:	Denys Vlasenko <vda.linux@...glemail.com>,
	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 01/20/2012 02:40 PM, Roland McGrath wrote:
> If you change the size of a regset, then the new full size will be the size
> of the core file notes.  Existing userland tools will not be expecting
> this, they expect a known exact size.  If you need to add new stuff, it
> really is easier all around to add a new regset flavor.  When adding a new
> one, you can make it variable-sized from the start so as to be extensible
> in the future.  We did this for NT_X86_XSTATE, for example.
> 
> Thanks,
> Roland

Hi Roland,

What is needed to make a regset variable-sized?  Just declaring that it
may change in size in the future, or does one need a length field at the
top (I would personally have expected that both notes and ptrace would
have out-of-band methods for getting the size?)

	-hp-a

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

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