linux-kernel - Re: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird crap with vdso on uml/i386)

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Message-ID: <4E5431F1.6040609@zytor.com>
Date:	Tue, 23 Aug 2011 16:04:17 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Lutomirski <luto@....edu>,
	Borislav Petkov <bp@...64.org>, Ingo Molnar <mingo@...nel.org>,
	"user-mode-linux-devel@...ts.sourceforge.net" 
	<user-mode-linux-devel@...ts.sourceforge.net>,
	Richard Weinberger <richard@....at>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.com>
Subject: Re: [uml-devel] SYSCALL, ptrace and syscall restart breakages (Re:
 [RFC] weird crap with vdso on uml/i386)

On 08/23/2011 02:20 PM, Linus Torvalds wrote:
> On Tue, Aug 23, 2011 at 2:08 PM, H. Peter Anvin <hpa@...or.com> wrote:
>>
>> Again, can we steal one of the padding fields to use for that state
>> variable?  We have two 16-bit padding fields; one for cs and one for ss.
> 
> We can steal them for passing the information to the user, but no, I
> don't think we can use them to then take the information *from* the
> user.
> 
> Somebody may well be setting up a 'pt_regs' structure on his own, and
> simply not fill in the padding, resulting in random data in those
> fields.
> 

That would be fine, I'd think... just gives the user space application
enough information to know how it would have to reshuffle the registers
if it needs to.

	-hpa

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