Re: [UNIKRAFT PATCH 1/3] build: Configure the compiler from command line

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

On 21.11.20 17:34, Vlad-Andrei Badoiu wrote:
> By default, the compiler is GCC. Use COMPILER=clang with make to configure the 
> compiler as CLANG.
>
> Signed-off-by: Alice Suiu <alicesuiu17@xxxxxxxxx>
> Signed-off-by: Vlad-Andrei Badoiu <vlad_andrei.badoiu@xxxxxx>
> ---
>   Makefile | 13 +++++++++++--
>   1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index 1f309b7d..b3ba38c4 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -544,11 +544,20 @@ ifneq ("$(origin CROSS_COMPILE)","undefined")
>   CONFIG_CROSS_COMPILE := $(CROSS_COMPILE:"%"=%)
>   endif
>   
> +# Use 'make COMPILER=clang' to compile with clang
> +ifeq ("$(origin COMPILER)", "command line")
> +  CONFIG_COMPILER := $(COMPILER)
> +endif
> +ifndef CONFIG_COMPILER
> +  CONFIG_COMPILER = gcc
> +endif
> +
> +
I think we should prefer a mechanism that works the same way as 
CROSS_COMPILE. This approach would be slightly more flexible (.config, 
environment variable, and command line) and would still cover your 
command line case:
ifneq ("$(origin COMPILER)","undefined")
CONFIG_COMPILER := $(COMPILER:"%"=%)
endif

We maybe need to add CONFIG_COMPILER to the `unexport` list (like we had 
to do for CONFIG_CROSS_COMPILE), but please double-check. It had to do 
with our nested sub-make call.
>   $(eval $(call 
> verbose_include,$(CONFIG_UK_BASE)/arch/$(UK_FAMILY)/Compiler.uk))
>   
>   # Make variables (CC, etc...)
> -LD             := $(CONFIG_CROSS_COMPILE)gcc
> -CC             := $(CONFIG_CROSS_COMPILE)gcc
> +LD             := $(CONFIG_CROSS_COMPILE)$(CONFIG_COMPILER)
> +CC             := $(CONFIG_CROSS_COMPILE)$(CONFIG_COMPILER)
>   CPP           := $(CC)
>   CXX           := $(CPP)
>   GOC           := $(CONFIG_CROSS_COMPILE)gccgo-7
Btw, the AR and NM commands, are there clang variants available, too?

AR := $(CONFIG_CROSS_COMPILE)$(CONFIG_COMPILER)-ar
NM := $(CONFIG_CROSS_COMPILE)$(CONFIG_COMPILER)-nm

If I remember correctly, something like this was needed when enabling 
LTO with gcc.