Re: [PATCH 3/5] build: arm64: provide -target and -march if using clang

[Julien Grall <julien@xxxxxxx>]

Hi Volodymyr,

On 29/11/2024 01:49, Volodymyr Babchuk wrote:
> Provide -target and -march explicitly when building with clang. This
> makes cross-compilation much easier, because clang accept this
> parameters regardless of host platform. Basically,
>
>    make XEN_TARGET_ARCH=arm64 clang=y llvm=y
>
> will behave in the same way if building Xen on x86, or on arm64 or on
> any other platform.
>
> -march is required because with default value, clang will not
> recognize EL2 registers.
Any chance this is happening because you are using "-target aarch64" 
rather than e.g. "arch64-arm-none-eabi"?
> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
> ---
>   config/arm64.mk | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/config/arm64.mk b/config/arm64.mk
> index c4662f67d0..97eb9a82e7 100644
> --- a/config/arm64.mk
> +++ b/config/arm64.mk
> @@ -5,6 +5,10 @@ CONFIG_XEN_INSTALL_SUFFIX :=
>   
>   CFLAGS += #-marm -march= -mcpu= etc
>   
> +ifeq ($(clang),y)
> +CFLAGS += -target aarch64 -march=armv8-a
AFAIU, -target is the triplet similar to what one would set 
CROSS_COMPILE. If you don't specify some values, then it will assume the 
compiler defaults. I am not sure this is a good idea as this could 
change between compilers. So should we set the triplet properly (e.g. 
arch64-arm-none-eabi) or maybe let the user specify it via CROSS_COMPILE?
Regarding -march=armv8-a, if you want to keep it, then I think it should 
be outside of the 'if' because this could also apply for GCC.
Cheers,

--
Julien Grall