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

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Date:	Fri, 24 Apr 2009 10:19:26 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Tim Abbott <tabbott@....EDU>
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>
Subject: Re: [PATCH v3 0/3] Add support for compiling with -ffunction-sections
 -fdata-sections

Tim Abbott wrote:
> On Mon, 20 Apr 2009, Linus Torvalds wrote:
> 
>> I'd be ok with merging it, but I haven't really gotten a strong feeling 
>> that anybody is going to enable it or use it.
> 
> Linus,
> 
> Would you be willing to merge the first 3 patches in this patch series at 
> this point?  I'm resending these patches to resolve some conflicts that 
> was recently introduced.

Hi Tim,

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?

If people use it and see it enough stable and useful, those patches
will be automatically pulled into linus kernel.


> To summarize the discussion, there are three uses for this code that have 
> significant interest.
> 
> One is decreasing the kernel size.  Denys Vlasenko has numbers that using 
> the linker's --gc-sections option (for which these patches are a 
> prerequisite) saves 10% of the kernel size when CONFIG_MODULES=n, and 1% 
> when CONFIG_MODULES=y.  Paul Mundt thinks many embedded users would use 
> this if it were available.
> 
> A related use is cleaning up a lot of ifdefs that exist only to decrease 
> the kernel size.  Several developers commented favorably on the direction 
> of using section garbage collection for dead code removal.
> 
> Finally, Ksplice depends on the option added by this patch series.
> 
> The first 3 patches in this patch series fix problems associated with 
> using -ffunction-sections.  As there are some architectures currently 
> using -ffunction-sections, these should ideally be merged now, especially 
> the first patch which involves scattered changes.

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

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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