Re: [PATCH v8 02/21] acpi: fix acpi_os_ioremap for arm64

[David Woodhouse]

On Wed, 2015-02-04 at 16:25 +0000, Russell King - ARM Linux wrote:
> I haven't experimented with it myself, but I think David Woodhouse
> has some experience in this area.

In many kernel configurations there are actually quite a lot of
functions that are never called, and I was quite surprised the first
time I played with this stuff.

There are a few ways of dealing with it. One is to use
-ffunction-section -fdata-sections --gc-sections as you noted. I once
also played with using GCC's --combine during the brief period that it
was supported and not *entirely* broken, with similar effects:
https://lwn.net/Articles/197097/

These days, the better answer is probably LTO. We could potentially
still look at --gc-sections, but I suspect we're better off using LTO
and just filing toolchain bugs until everything that --gc-sections
*would* have dropped is also dropped from the LTO build :)

Unless --gc-sections actually speeds up the build in a significant way;
a full LTO link of the kernel takes insane amounts of memory IIRC.

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@xxxxxxxxx                              Intel Corporation

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