Re: [PATCH v6 3/6] LoongArch: Use model("extreme") attribute for per-CPU variables in module if CONFIG_AS_HAS_EXPLICIT_RELOCS

[Xi Ruoyao]

On Mon, 2022-08-29 at 21:31 +0800, Xi Ruoyao wrote:
> diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile
> index 1563747c4fa8..593818a61741 100644
> --- a/arch/loongarch/Makefile
> +++ b/arch/loongarch/Makefile
> @@ -53,6 +53,9 @@ LDFLAGS_vmlinux                       += -G0 -static -n -nostdlib
>  # combination of a "new" assembler and "old" compiler is not supported.  Either
>  # upgrade the compiler or downgrade the assembler.
>  ifdef CONFIG_AS_HAS_EXPLICIT_RELOCS
> +ifeq ($(shell echo '__has_attribute(model)' | $(CC) -E -P - 2> /dev/null), 0)
> +$(error "C compiler must support model attribute if using explicit relocs")
> +endif

Self review:

I'm wondering if we really need this thing...  There won't be a GCC
version released with explicit relocation but without model attribute
(GCC 13 starts to support them both).

But without a check, if someone uses an early GCC 13 snapshot and
ignores the -Wattributes warning, the system will suddenly blow up
loading a module with per-CPU variable defined.

Maybe "-Werror=attributes" is better, but is it OK to add a -Werror=
option for entire Linux tree?

>  cflags-y                       += -mexplicit-relocs
>  else
>  cflags-y                       += $(call cc-option,-mno-explicit-relocs)

-- 
Xi Ruoyao <xry111@xxxxxxxxxxx>
School of Aerospace Science and Technology, Xidian University