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

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Date:	Tue, 24 Jan 2012 09:19:32 +0100
From:	"Indan Zupancic" <indan@....nu>
To:	"Roland McGrath" <mcgrathr@...gle.com>
Cc:	"Denys Vlasenko" <vda.linux@...glemail.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"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 Fri, January 20, 2012 23:40, 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.

If stuffing it into eflags is not acceptable and you really want a
new regset, perhaps that new regset should only contain the new,
mostly cross-platform information, instead of slapping it at the
end of the x86 regset. Because if you do the latter you really
could have better just stuffed it into eflags.

Greetings,

Indan


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