[U-Boot] [RFC PATCH 1/2] armv7: enable Thumb build for armv7

[Aneesh V <aneesh@ti.com>]

Albert,

On Wednesday 16 March 2011 10:55 PM, Albert ARIBAUD wrote:
> Le 16/03/2011 09:39, Aneesh V a ?crit :
[snip ..]
>
> Some toolchains in current use (notably the one provided with ELDK 4.2,
> and possibly others) do not support -march=armv7[-a]. Do we really need
> armv7 instructions?

'cc-option' will make sure that build won't break for old compilers. We
can do something like this:

PLATFORM_CPPFLAGS += $(call cc-option,-march=armv7-a, -march=armv5)

We are not planning to use armv7-a instructions in the code. In fact,
recently I removed even an armv5 instruction from armv7 generic code in
the interest of not breaking Tegra2.

However, keeping -march=armv7-a (armv6 and above) helps in having
Thumb2, which I believe is a good compromise between code density and
performance.

So, OMAP4 U-Boot when built with ELDK will give you Thumb1 code where
as when it is built with newer compilers it will give you Thumb2 code.
As long we don't use non-compliant assembly instructions, both should
build and work fine.

br,
Aneesh