linux-kernel - Re: [PATCH v3 0/3] Add support for compiling with -ffunction-sections -fdata-sections

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Message-ID: <alpine.DEB.1.10.0904241057440.23249@vinegar-pot.mit.edu>
Date:	Fri, 24 Apr 2009 11:32:55 -0400 (EDT)
From:	Tim Abbott <tabbott@....EDU>
To:	Masami Hiramatsu <mhiramat@...hat.com>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Anders Kaseorg <andersk@....edu>,
	Waseem Daher <wdaher@....edu>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Andi Kleen <andi@...stfloor.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Jeff Arnold <jbarnold@....edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jon Masters <jonathan@...masters.org>,
	"Theodore Ts'o" <tytso@....edu>,
	Nikanth Karthikesan <knikanth@...e.de>,
	Arjan van de Ven <arjan@...radead.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	Américo Wang <xiyou.wangcong@...il.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Kyle McMaartin <kyle@...artin.ca>,
	David Howells <dhowells@...hat.com>
Subject: Re: [PATCH v3 0/3] Add support for compiling with -ffunction-sections
 -fdata-sections

On Fri, 24 Apr 2009, Masami Hiramatsu wrote:

> What would you think about posting these patches plus -ffunction-sections/
> -fdata-sections patch to -mm tree, -tip tree, or -next tree as
> "playable" Ksplice patchset?

The section rename patch often merge conflicts with other changes.  I 
think that having it sit out in one of those trees for another release 
would result in a lot of unnecessary work rebasing patches between that 
tree and Linus' tree.

Once these -ffunction-sections support patches are merged, I intend to 
post the rest of the Ksplice patchset for one of those trees.

> If there are actual problems on those arch, I think you'd better post
> these patches as bugfixes with bug reports.

These problems are all discussed in the commit messages of the relevant 
patches.

One patch fixes modposting a kernel with more than 65536 ELF sections.  
It is certainly possible to get this many with allyesconfig and 
-ffunction-sections -fdata-sections.

Another fixes the issue that when you build with -ffunction-sections, 
modpost will print a large number of spurious warnings when it sees 
sections like .rodata.__func__.12345 which are generated by the __FUNC__ 
macro.

The patch with many scattered changes fixes the problem that with 
-ffunction-sections -fdata-sections, a function named head gets put in the 
".text.head" section, and your "static int percpu" ends up in the 
".data.percpu" section and probably ends up being made percpu.  This is a 
potentially nasty problem.

	-Tim Abbott
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