On Tue, Nov 10, 2020 at 9:11 PM 'Nick Desaulniers' via Clang Built
Linux <clang-built-li...@googlegroups.com> wrote:
>
> On Tue, Nov 10, 2020 at 12:10 PM Jian Cai <jian...@google.com> wrote:
> >
> > I tried to verify with ixp4xx_defconfig, and I noticed it also used
> > CONFIG_CPU_BIG_ENDIAN=y to enable big endianness as follows,
> >
> > linux$ grep ENDIAN arch/arm/configs/ixp4xx_defconfig
> > CONFIG_CPU_BIG_ENDIAN=y
> >
> > Also it appeared arch/arm/kernel/iwmmxt.o was not built with
> > ixp4xx_defconfig. The commands I used
> >
> > linux$ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make CC=clang
> > ixp4xx_defconfig
> > linux$ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- make -j32 CC=clang
> > linux$ ls arch/arm/kernel/iwmmxt.o
> > ls: cannot access 'arch/arm/kernel/iwmmxt.o': No such file or directory
> >
> > Did I miss any steps?
>
> Yes, you need to manually enable CONFIG_IWMMXT in menuconfig or via
> `scripts/configs -e`.
To clarify: ixp4xx and pxa3xx were two platforms based on the XScale core.
ixp4xx was commonly used in big-endian mode but lacked iWMMXt. pxa3xx
had iWMMXt but doesn't allow enabling big-endian mode because of a Kconfig
dependency, meaning that nobody has ever tried it, and it's likely broken.
Later 'mvebu' parts (Armada 510) do have iWMMXt and allow big-endian
mode, but those are BE8, with non-reversed byteorder for the instructions.
So none of this matters in practice, but it's very satifiying to know
it is finally
all working with the integrated assembler in all those combinations, at
least in theory!
Arnd
