[RFC PATCH 1/3] ARM: iwmmxt: Fix Makefile rules for building iwmmxt for Thumb-2

[Eric Miao]

On Wed, Sep 7, 2011 at 8:59 AM, Dave Martin <dave.martin at linaro.org> wrote:
> Because gcc/gas have no sane way to turn on individual CPU
> extensions from the command-line, iwmmxt.S was previously built
> with -mcpu=iwmmxt.  Unfortunately, this also downgrades the CPU to
> v5, with the result that this file fails to build for a Thumb-2
> kernel.
>
> New versions of the tools support -march=<base arch>+iwmmxt, and it
> seems reasonable to require up-to-date tools when building in
> Thumb-2.  So, this patch uses -march=armv7-a+iwmmxt for
> CONFIG_THUMB2_KERNEL=y.
>
> Signed-off-by: Dave Martin <dave.martin at linaro.org>
> ---
>  arch/arm/kernel/Makefile |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
>
> diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
> index f7887dc..8a58339 100644
> --- a/arch/arm/kernel/Makefile
> +++ b/arch/arm/kernel/Makefile
> @@ -65,7 +65,14 @@ obj-$(CONFIG_CPU_PJ4)                += pj4-cp0.o
>  obj-$(CONFIG_IWMMXT)           += iwmmxt.o
>  obj-$(CONFIG_CPU_HAS_PMU)      += pmu.o
>  obj-$(CONFIG_HW_PERF_EVENTS)   += perf_event.o
> +
> +# When enough people have binutils which support -march=...+iwmmxt, this
> +# should change to something like if __LINUX_ARM_ARCH__ < 7.
> +ifdef CONFIG_THUMB2_KERNEL
> +AFLAGS_iwmmxt.o                        := -Wa,-march=armv7-a+iwmmxt
> +else
>  AFLAGS_iwmmxt.o                        := -Wa,-mcpu=iwmmxt
> +endif

It looks more like the switch should depend on the compiler version.
Unless there is a clear way to decide if gcc supports this switch, I
think it's reasonable to have the change like above.

>
>  ifneq ($(CONFIG_ARCH_EBSA110),y)
>   obj-y                += io.o
> --
> 1.7.4.1
>
>