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	Tue, 31 Mar 2015 12:27:36 -0400
Date: Tue, 31 Mar 2015 17:27:22 +0100
From: Dave Martin <Dave.Martin@arm.com>
Subject: Re: [RFC PATCH 2/2] Kbuild: avoid partial linking of
 drivers/built-in.o
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To: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>, Michal Marek <mmarek@suse.cz>, Russell King - ARM Linux <linux@arm.linux.org.uk>, Arnd Bergmann <arnd@arndb.de>, linux-kbuild@vger.kernel.org, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>

On Tue, Mar 31, 2015 at 11:22:29AM -0400, Nicolas Pitre wrote:
> On Mon, 30 Mar 2015, Ard Biesheuvel wrote:
> 
> > On 30 March 2015 at 16:13, Michal Marek <mmarek@suse.cz> wrote:

[...]

> > > What you could do is to add a Kconfig option to arch/arm/Kconfig adding
> > > -ffunction-sections to the compiler flags. Then allyesconfig would
> > > select it and work around the problem in a somewhat elegant way.
> > >
> > 
> > Excellent idea! Arnd hasn't chimed in yet, but he is the one doing
> > lots and lots of randconfig builds and other test builds, so I will
> > wait for him to confirm that this is a useful thing to have.
> 
> I'm using -ffunction-sections as well for the kernel size reduction work 
> I'm currently doing.  The linker script has to be adapted so .text.* is 
> specified along .text otherwise those functions end up appended at the 
> end of the binary.

Interesting ... do you also mean using --gc-sections at link time?
We'd need to avoid pruning needed code that has no explicit caller,
and functions that are part of the kernel/module ABI but not used
within vmlinux.

The GCC docs suggest that -ffunction-sections may impact performance
and/or increase code size, but I don't know by how much.  Maybe it
interferes with inling.

Cheers
---Dave