linux-kernel - Re: [PATCH] [PATCH v2] riscv: add as-options for modules with assembly compontents

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Date:   Thu, 21 Jul 2022 12:53:16 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     ben.dooks@...ethink.co.uk
CC:     linux-kernel@...ts.codethink.co.uk,
        linux-riscv@...ts.infradead.org, aou@...s.berkeley.edu,
        linux-kernel@...r.kernel.org, ben.dooks@...ethink.co.uk,
        Bin Meng <bmeng.cn@...il.com>
Subject:     Re: [PATCH] [PATCH v2] riscv: add as-options for modules with assembly compontents

On Sun, 29 May 2022 08:22:00 PDT (-0700), ben.dooks@...ethink.co.uk wrote:
> When trying to load modules built for RISC-V which include assembly files
> the kernel loader errors with "unexpected relocation type 'R_RISCV_ALIGN'"
> due to R_RISCV_ALIGN relocations being generated by the assembler.
>
> The R_RISCV_ALIGN relocations can be removed at the expense of code space
> by adding -mno-relax to gcc and as.  In commit 7a8e7da42250138
> ("RISC-V: Fixes to module loading") -mno-relax is added to the build
> variable KBUILD_CFLAGS_MODULE. See [1] for more info.
>
> The issue is that when kbuild builds a .S file, it invokes gcc with
> the -mno-relax flag, but this is not being passed through to the
> assembler. Adding -Wa,-mno-relax to KBUILD_AFLAGS_MODULE ensures that
> the assembler is invoked correctly. This may have now been fixed in
> gcc[2] and this addition should not stop newer gcc and as from working.
>
> [1] https://github.com/riscv/riscv-elf-psabi-doc/issues/183
> [2] https://github.com/gcc-mirror/gcc/commit/3b0a7d624e64eeb81e4d5e8c62c46d86ef521857
>
> Notes:
>
> Signed-off-by: Ben Dooks <ben.dooks@...ethink.co.uk>
> Reviewed-by: Bin Meng <bmeng.cn@...il.com>
> ---
>  arch/riscv/Makefile | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index 1f5c03082976..fca40511a8c6 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -60,6 +60,7 @@ ifeq ($(CONFIG_PERF_EVENTS),y)
>  endif
>
>  KBUILD_CFLAGS_MODULE += $(call cc-option,-mno-relax)
> +KBUILD_AFLAGS_MODULE += $(call as-option,-Wa$(comma)-mno-relax)
>
>  # GCC versions that support the "-mstrict-align" option default to allowing
>  # unaligned accesses.  While unaligned accesses are explicitly allowed in the

Sorry for being so slow here, I've gotten pretty buried and it wasn't 
clear this was a fix.  I put it in fixes with some tags.

Thanks!