linux-kernel - Re: [PATCH v2 1/5] x86/boot/compressed: prefer cc-option for CFLAGS additions

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Date:   Wed, 31 Aug 2022 12:41:47 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Tom Rix <trix@...hat.com>, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, x86@...nel.org,
        Dmitrii Bundin <dmitrii.bundin.a@...il.com>,
        Fangrui Song <maskray@...gle.com>,
        Alexey Alexandrov <aalexand@...gle.com>,
        Bill Wendling <morbo@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Arvind Sankar <nivedita@...m.mit.edu>
Subject: Re: [PATCH v2 1/5] x86/boot/compressed: prefer cc-option for CFLAGS
 additions

On Wed, Aug 31, 2022 at 11:44:04AM -0700, Nick Desaulniers wrote:
> We have an issue where as-option is testing new options with accumulated
> CFLAGS. This makes it so that we can't use as-option to update AFLAGS
> since many CFLAGS aren't valid AFLAGS. This is being fixed in a follow
> up patch. Before doing so, move the assembler test for
> -Wa,-mrelax-relocations=no from using as-option to cc-option.

I think the first couple of sentences might sound clearer without the
"we". Maybe something like the following?

"as-option tests new options using KBUILD_CFLAGS, which causes problems
when using as-option to update KBUILD_AFLAGS because many compiler
options are not valid assembler options."

> Cc: Arvind Sankar <nivedita@...m.mit.edu>
> Cc: x86@...nel.org
> Link: https://lore.kernel.org/llvm/CAK7LNATcHt7GcXZ=jMszyH=+M_LC9Qr6yeAGRCBbE6xriLxtUQ@mail.gmail.com/
> Suggested-by: Masahiro Yamada <masahiroy@...nel.org>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>

Regardless of the commit message:

Reviewed-by: Nathan Chancellor <nathan@...nel.org>

Additionally, I did verify that '-Wa,-mrelax-relocations=no' still shows
up in arch/x86/boot/compressed so:

Tested-by: Nathan Chancellor <nathan@...nel.org>

> ---
> Changes v1 -> v2:
> * Split off of v1 [1/3].
> * Use cc-option to update CFLAGS, as per Masahiro.
> * Add Masahiro's Suggested-by, Cc Arvind.
> 
>  arch/x86/boot/compressed/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index 35ce1a64068b..85934204d905 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -49,7 +49,7 @@ KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
>  KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
>  KBUILD_CFLAGS += -D__DISABLE_EXPORTS
>  # Disable relocation relaxation in case the link is not PIE.
> -KBUILD_CFLAGS += $(call as-option,-Wa$(comma)-mrelax-relocations=no)
> +KBUILD_CFLAGS += $(call cc-option,-Wa$(comma)-mrelax-relocations=no)
>  KBUILD_CFLAGS += -include $(srctree)/include/linux/hidden.h
>  
>  # sev.c indirectly inludes inat-table.h which is generated during
> -- 
> 2.37.2.672.g94769d06f0-goog
>