linux-kernel - Testing of function/data-sections on linux-2.6.35-rc4

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Date:	Sun, 18 Jul 2010 17:03:16 +0200
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Tim Abbott <tabbott@...lice.com>, Tim Bird <tim.bird@...sony.com>
Cc:	James Bottomley <James.Bottomley@...senpartnership.com>,
	linux-kernel@...r.kernel.org,
	Matt Fleming <matt@...sole-pimps.org>,
	linux-arch@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
	Sam Ravnborg <sam@...nborg.org>, Michal Marek <mmarek@...e.cz>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Parisc List <linux-parisc@...r.kernel.org>
Subject: Testing of function/data-sections on linux-2.6.35-rc4

Hi Tim, Tim, folks,

Update on -ffunction-sections status:

I re-tested linux-2.6.35-rc4 today.

Most of work needed for -ffunction-sections -fdata-sections
is already in this kernel. This mail explains what is
still missing.

In order to have a working kernel with this make invocation:

	make KCFLAGS="-ffunction-sections -fdata-sections"

linux-2.6.35-rc4 needs three patches:

* modpost fix for 64k+ sections: linux-2.6.35-rc4-fs.modpost.patch
  This patch is in -mm, it still not reach mainline...

* fix for kernel linker stripts: linux-2.6.35-rc4-fs.fix-kernel-linker-scripts.patch
  It makes _all_ linker scripts -ffunction/data-sections safe via:
  -       *(.data)
  +       *(.data .data.*)

* fix for module linker script: linux-2.6.35-rc4-fs.fix-ko-module-linker-script.patch
  Prevents kernel modules from having unnecessarily many
  sections and thus prevents module size growth.

Then, in order to also garbage-collect the sections, I added

LDFLAGS_vmlinux += --gc-sections

in top-level Makefile.

This requires the additional patch (linux-2.6.35-rc4-fsgs.patch)
which adds KEEP(section) directives to kernel linker stripts.
Otherwise, linker will discard some crucial sections.

All four patches are attached.

I am sending this email from the machine which runs the kernel
built with -ffunction-sections -fdata-sections --gc-sections.

-- 
vda

View attachment "linux-2.6.35-rc4-fs.modpost.patch" of type "text/x-diff" (9268 bytes)

View attachment "linux-2.6.35-rc4-fs.fix-kernel-linker-scripts.patch" of type "text/x-diff" (13646 bytes)

View attachment "linux-2.6.35-rc4-fs.fix-ko-module-linker-script.patch" of type "text/x-diff" (1213 bytes)

View attachment "linux-2.6.35-rc4-fsgs.patch" of type "text/x-diff" (15581 bytes)