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

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Date:	Thu, 26 Jan 2012 19:03:43 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Indan Zupancic <indan@....nu>, Oleg Nesterov <oleg@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Jamie Lokier <jamie@...reable.org>,
	Andrew Lutomirski <luto@....edu>,
	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!?

Hi Linus,

On Thu, Jan 26, 2012 at 4:47 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>> Please look at strace source, get_scno() function, where
>> it reads syscall no and parameters. Let's see....
>> - POWERPC: has 32-bit and 64-bit mode
>> - X86_64: has 32-bit and 64-bit mode
>> - IA64: has i386-compat mode
>> - ARM: has more than one ABI
>> - SPARC: has 32-bit and 64-bit mode
>>
>> Do you want to re-invent a different arch-specific way to report
>> syscall type for each of these arches?
>
> I think an arch-specific one is better than trying to make some
> generic one that is messy.
>
> As you say, many architectures have multiple system call ABIs.
>
> But they tend to be very *different* issues. They can be about
> multiple ABI's, as you mention, and even when they *look* similar
> (32-bit vs 64-bit ABI's) they are actually totally different issues.
> [skip]

I don't have a particular attachment to my solution,
and I think we already talk about this problem for
far too long.

Looks like nobody is _strongly_ opposed to your patch
which uses a few bits in eflags to report bitness
of the x86 syscall.

Lets just do that already. If you commit it to kernel git,
I will immediately change strace accordingly.

-- 
vda
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