linux-kernel - Re: [PATCHv2 1/4] x86_64: cleanup THREAD

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Message-Id: <1421866125.216465.217011617.2AC1A809@webmail.messagingengine.com>
Date:	Wed, 21 Jan 2015 19:48:45 +0100
From:	Alexander van Heukelum <heukelum@...tmail.fm>
To:	Borislav Petkov <bp@...e.de>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	Andy Lutomirski <luto@...capital.net>, X86 ML <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Oleg Nesterov <oleg@...hat.com>, Rik van Riel <riel@...hat.com>
Subject: Re: [PATCHv2 1/4] x86_64: cleanup THREAD_INFO(reg,offset) macro

On Wed, Jan 21, 2015, at 19:04, Borislav Petkov wrote:
> On Wed, Jan 21, 2015 at 05:20:09PM +0100, Alexander van Heukelum wrote:
> > On Wed, Jan 21, 2015, at 14:40, Denys Vlasenko wrote:
> > > On Sun, Jan 18, 2015 at 12:45 PM, Alexander van Heukelum
> > > <heukelum@...tmail.fm> wrote:
> > > > The macro THREAD_INFO(reg,offset) is used in assembly to compute the
> > > > offset between the user ptregs and the thread_info struct. Change
> > > > the macro and all its uses so that offset is given as the current
> > > > top of stack in the pt_regs frame. The generated code is identical.
> > > 
> > > What is the purpose of doing this?
> > > 
> > > I don't mean to say that it's pointless, but it is also not obvious
> > > why it's better than the code before patch.
> > 
> > Just because I had a hard time understanding what the offset
> > parameter means. Turns out Borislav did another variant in his
> > patchset. Quoting him from the commit message which made
> > that the change:
> > > Semi-mysterious expressions THREAD_INFO(%rsp,RIP) - "why RIP??"
> > > are now replaced by more logical THREAD_INFO(%rsp,SIZEOF_PTREGS) -
> > > "rsp is SIZEOF_PTREGS bytes below the top, calculate
> > > thread_info's address using that information"
> > 
> > Borislav expresses "offset" as an offset from the stack's page
> > boundary,while I chose the offset from the start of struct
> > pt_regs on the stack.
> 
> I've never done any such thing :-)
> 
> s/Borislav/Denys/g.

twice ... and stop using third person too... Oops.

Err. sorry :-/.
 
> -- 
> Regards/Gruss,
>     Boris.
> 
> ECO tip #101: Trim your mails when you reply.
> --
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