linux-kernel - Re: [PATCH 3/3] build system: section garbage collection for vmlinux

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Message-Id: <200709111223.04724.vda.linux@googlemail.com>
Date:	Tue, 11 Sep 2007 12:23:04 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] build system: section garbage collection for vmlinux

On Monday 10 September 2007 20:14, Sam Ravnborg wrote:
> On Mon, Sep 10, 2007 at 08:02:15PM +0100, Denys Vlasenko wrote:
> > On Monday 10 September 2007 13:01, Sam Ravnborg wrote:
> > > > 
> > > > > Doing a normal kernel build will link vmlinux three or four times.
> > > > > If we introduce --gc-sections we should add a preparational link of
> > > > > vmlinux where we use --gc-sections and skip it for the rest of the links
> > > > > assuming that --gc-sections takes some time for ld to do.
> > > > 
> > > > Yes, this will speed up things a bit.
> > > 
> > > If we do the --gc-sections trick during the preparational link then we do
> > > not use the arch supplied linker script.
> > > Will it be possible to create a dedicated linker script that is valid
> > > for all architectures and which only include the KEEP() directives for
> > > the diverse sections?
> > 
> > Unfortunately, -r and --gc-sections don't mix.
> > 
> > x86_64-pc-linux-gnu-ld: --gc-sections and -r may not be used together
>
> OK - so much for that optimization :-(
> 
> But then we need to annotate ALL arch linker script before introducing this.
> And that bring me back to that we should put some sanity into these first.

I was working with x86_64 ld script and am willing to clean it up a bit.

I can impelment and test DISCARD_UNUSED_SECTIONS for x86_64 and later
for i386.

Other arches can follow when they find it interesting/worthwhile.

At first, big scary warning under "config DISCARD_UNUSED_SECTIONS"
should be enough to make people avoid it for production boxes, I hope.

Should I send next round of patches to you or to Andrew?
--
vda
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