linux-kernel - Re: [PATCH] x86/asm/entry/64: Merge the field offset into the THREAD

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Message-ID: <20150324192926.GA23521@gmail.com>
Date:	Tue, 24 Mar 2015 20:29:26 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/asm/entry/64: Merge the field offset into the
 THREAD_INFO() macro


* Denys Vlasenko <dvlasenk@...hat.com> wrote:

> On 03/24/2015 07:44 PM, Ingo Molnar wrote:
> > From 11e2761ba0969466299b7109eba749d2292e8796 Mon Sep 17 00:00:00 2001
> > From: Ingo Molnar <mingo@...nel.org>
> > Date: Tue, 24 Mar 2015 19:18:41 +0100
> > Subject: [PATCH] x86/asm/entry/64: Merge the field offset into the THREAD_INFO() macro
> > 
> > Before:
> > 
> >    TI_sysenter_return+THREAD_INFO(%rsp,3*8),%r10d
> > 
> > After:
> > 
> >    movl    THREAD_INFO(TI_sysenter_return, %rsp, 3*8), %r10d
> > 
> > to turn it into a clear thread_info accessor.
> 
> Good idea, I also wanted to do this.
> I propose a more C-like order of arguments instead.
> In C, field names are on the right: obj.field, ptr->field.
> 
>     THREAD_INFO(%rsp, 3*8, TI_field_name)
> 
> would suggest to the reader a pseudo-C construct:
> 
>     THREAD_INFO(sp, offset)->field_name

So I picked that order, because the C code we want to emulate here 
visually is:

	thread_info->field_name

and visually this order represents just that:

	THREAD_INFO(TI_field_name, ...)

" ,%reg, offset" in that sense is just a 'detail' to how to access 
thread_info.

That order also resembles the assembly format more, which is usually 
in field(reg) order, i.e.:

	THREAD_INFO(field, %reg, ...)

Hm?

Thanks,

	Ingo
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