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

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Message-ID: <4F35A0A6.8020600@zytor.com>
Date:	Fri, 10 Feb 2012 14:56:38 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Indan Zupancic <indan@....nu>
CC:	"H.J. Lu" <hjl.tools@...il.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,
	Roland McGrath <mcgrathr@...omium.org>
Subject: Re: Compat 32-bit syscall entry from 64-bit task!?

On 02/10/2012 02:42 PM, Indan Zupancic wrote:
>> #include <stdnak.h>
> 
> Could you please elaborate? Is it just the stealing of eflags bits that
> irks you or are there technical problems too?

Yes, I will not accept that unless it gets ok'd by the architecture
people, which may take a long time.

> I understand some people would prefer a new regset, but that would force
> everyone to use PTRACE_GETREGSET instead of whatever they are using now.
> The problem with that is that not all archs support PTRACE_GETREGSET, so
> the user space ptrace code needs to use different ptrace calls depending
> on the architecture for no good reason. If PEEK_USER works then it's less
> of a problem, then it's one extra ptrace call compared to the eflag way
> if PTRACE_GETREGS is used. If this new info is exposed with a special
> regset instead of being appended to normal regs then one extra ptrace
> call per system call event needs to be done. You can as well add special
> x86 ptrace requests then.

Seriously... if you're mucking with registers on this level, youan
architecture dependency is not a big deal, and perhaps it's a good sign
that the laggard architectures need to catch up.  If multiple ptrace
requests is a problem, then perhaps this is a good sign that we need a
single way to get multiple regsets in a single request?

> Or is the main advantage of using a regset that it shows up in coredumps?
> That would merit the extra effort at least.

That is another plus, which is significant, too.  The final advantage is
expandability.

	-hpa

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

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