linux-kernel - Re: [PATCH] ARM: move body of head-common.S back to text section

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Message-ID: <20130704002235.GL22702@windriver.com>
Date:	Wed, 3 Jul 2013 20:22:35 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Stephen Warren <swarren@...dotorg.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Will Deacon <will.deacon@....com>,
	<linux-kernel@...r.kernel.org>, Joseph Lo <josephl@...dia.com>,
	<linux-tegra@...r.kernel.org>, Stephen Warren <swarren@...dia.com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: move body of head-common.S back to text section

[Re: [PATCH] ARM: move body of head-common.S back to text section] On 03/07/2013 (Wed 18:20) Russell King - ARM Linux wrote:

> On Wed, Jul 03, 2013 at 11:30:12AM -0400, Paul Gortmaker wrote:
> > [Re: [PATCH] ARM: move body of head-common.S back to text section] On 03/07/2013 (Wed 11:00) Russell King - ARM Linux wrote:
> > 
> > > On Wed, Jul 03, 2013 at 01:19:07AM -0400, Paul Gortmaker wrote:
> > > > As an aside, I'm now thinking any __INIT that implicitly rely on EOF for
> > > > closure are nasty traps waiting to happen and it might be worthwhile to
> > > > audit and explicitly __FINIT them before someone appends to the file...
> > > 
> > > That hides a different kind of bug though - I hate __FINIT for exactly
> > > that reason.  Consider this:
> > 
> > Agreed - perhaps masking that it is a ".previous" just hides the fact
> > that it is more like a pop operation vs. an on/off operation, or per
> > function as we have in C.
> 
> I read the info pages, because I thought it was a pop operation too.
> I was concerned that .section didn't push the previous section onto the
> stack.
> 
> However, .popsection is the pseudio-op which pops.  .previous just toggles
> the current section with the section immediately before it.
> 
> So:
> 
> 	.text
> 	.data
> 	.previous
> 	/* this is .text */
> 	.previous
> 	/* this is .data */
> 	.previous
> 	/* this is .text */
> 	.previous
> 	/* this is .data */

Cool -- I bet we weren't the only ones thinking it was a pop.  Thanks.

Does that make __FINIT less evil than we previously assumed?  I think
your example was the following pseudo-patch:


	.text
	<some text>
+	.data
+ 	<some data>
	__INIT
	<big hunk of init>
	__FINIT
	/* this below used to be text */
	<more stuff that was originally meant for text>

Even if it is a toggle (vs. pop), the end text will now become data,
so the no-op __FINIT with an explicit section called out just below
it may still be the most unambiguous way to indicate what is going on.

> 
> > That seems reasonable to me.  I can't think of any self auditing that is
> > reasonably simple to implement.  One downside of __FINIT as a no-op vs.
> > what it is today, is that a dangling __FINIT in a file with no other
> > previous sections will emit a warning.  But that is a small low value
> > corner case I think.
> 
> That warning from __FINIT will only happen if there has been no section
> or .text or .data statement in the file at all.  As soon as you have any
> statement setting any kind of section, .previous doesn't warn.
> 
> So:
> 
> 	.text
> 	...
> 	__FINIT
> 
> produces no warning.o

Yep -- we are both saying the same thing here - hence why I called it a
small low value corner case.
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