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

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Message-ID: <CA+55aFzrHaJUKgUCx1uaeuqcyzZuUwQLiGj9dP5D3m-xt6v2SA@mail.gmail.com>
Date:	Wed, 18 Jan 2012 13:26:36 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	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,
	Roland McGrath <mcgrathr@...omium.org>
Subject: Re: Compat 32-bit syscall entry from 64-bit task!?

On Wed, Jan 18, 2012 at 1:04 PM, H. Peter Anvin <hpa@...or.com> wrote:
>
> Fair enough.  Sigh.  I still think an actual pseudo-register would be
> better.

.. and that breaks existing binaries too, because the indexing is
based on offsets into "struct pt_regs", and while we *could* change
that - leave pt_regs untouched but add a new virtual register - it
would be problematic.

We could add a whole new ptrace() access command (eg
PTRACE_GETSYSTEMREGSET), of course. But that's a lot of effort for
very little gain.

So on the whole, putting it in eflags seemed like the *much* simpler approach.

                 Linus
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