Re: [PATCH v5.99.1 RFC 1/4] xen/arm: Duplicate gic-v2.c file to support hip04 platform version

[Ian Campbell <ian.campbell@citrix.com>]

On Wed, 2015-02-25 at 16:34 +0000, Stefano Stabellini wrote:
> I think we should disable the build of all drivers in Xen by default,
> except for the ARM standard compliant ones (for aarch64 the SBSA is a
> nice summary of what is considered compliant), to keep the size of the
> binary small.

I think this last statement was based on information that the gic-v2
driver was of the order of 70-100K in size, but I think that information
was wrong (I suspect it was the raw .o size, which includes debug info
and other extraneous bits). Here I see:

$ du -h xen/arch/arm/gic-v2.o
148K	xen/arch/arm/gic-v2.o
$ aarch64-linux-gnu-size xen/arch/arm/gic-v2.o 
   text	   data	    bss	    dec	    hex	filename
   6619	      0	     97	   6716	   1a3c	xen/arch/arm/gic-v2.o

IOW the actual binary size is on the order of 6K (gic-v3.o is around the
same). This is arm64, I can't be bothered to rebuild for arm32, it'll be
similar.

Given that then I really don't think it is worth introducing a two tier
build over it.

If we really cared about these sorts of savings we would arrange to
discard all of the unused GIC/SMMU/UART driver's .text/.data/.bss after
boot (easy enough to achieve by putting each in a dedicated segment).

But I don't think we have enough such drivers to start worrying about
doing that just now. We have that opportunity in our back pocket if we
ever get to that point, which is good enough I think.

> Could you please introduce a Xen build time option in
> xen/arch/arm/Rules.mk, called HAS_NON_STANDARD_DRIVERS, that by default
> is n, and gate the build of gic-hip04.c on it?

Frediano, I see you've already done so in v6, thanks for that. Sorry to
go back on it.

Assuming the rest of the series in v6 is OK (gets acked and whatever)
then I expect I can just skip that one patch when applying and fixup the
Makefile in the obvious way (approx s/HAS_NON.../CONFIG_ARM32/) in the
dependent patch.

Ian.