linux-kernel - Re: [PATCH 2/2] kconfig: unify cc-option and as-option

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Date:   Mon, 15 Jun 2020 11:00:08 +0100
From:   Will Deacon <will@...nel.org>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Changbin Du <changbin.du@...el.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] kconfig: unify cc-option and as-option

On Sun, Jun 14, 2020 at 11:43:41PM +0900, Masahiro Yamada wrote:
> cc-option and as-option are almost the same; both pass the flag to
> $(CC). The main difference is the cc-option stops before the assemble
> stage (-S option) whereas as-option stops after it (-c option).
> 
> I chose -S because it is slightly faster, but $(cc-option,-gz=zlib)
> returns a wrong result (https://lkml.org/lkml/2020/6/9/1529).
> It has been fixed by a separate patch, but using -c is more robust.
> 
> However, you cannot simply replace -S with -c because the following
> code would break:
> 
>     depends on $(cc-option,-gsplit-dwarf)
> 
> The combination of -c and -gsplit-dwarf does not accept /dev/null as
> output.
> 
>   $ cat /dev/null | gcc -gsplit-dwarf -S -x c - -o /dev/null
>   $ echo $?
>   0
> 
>   $ cat /dev/null | gcc -gsplit-dwarf -c -x c - -o /dev/null
>   objcopy: Warning: '/dev/null' is not an ordinary file
>   $ echo $?
>   1
> 
>   $ cat /dev/null | gcc -gsplit-dwarf -c -x c - -o tmp.o
>   $ echo $?
>   0
> 
> There is another flag that creates an separate file based on the
> object file path:
> 
>   $ cat /dev/null | gcc -ftest-coverage -c -x c - -o /dev/null
>   <stdin>:1: error: cannot open /dev/null.gcno
> 
> So, we cannot use /dev/null to sink the output.
> 
> Align the cc-option implementation with scripts/Kbuild.include.
> 
> With -c option used in cc-option, as-option is unneeded.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---
> 
>  arch/arm64/Kconfig      | 2 +-
>  lib/Kconfig.debug       | 1 -
>  scripts/Kconfig.include | 8 +-------
>  3 files changed, 2 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 31380da53689..6eb18f45258e 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1564,7 +1564,7 @@ config CC_HAS_SIGN_RETURN_ADDRESS
>  	def_bool $(cc-option,-msign-return-address=all)
>  
>  config AS_HAS_PAC
> -	def_bool $(as-option,-Wa$(comma)-march=armv8.3-a)
> +	def_bool $(cc-option,-Wa$(comma)-march=armv8.3-a)

For this arm64 part:

Acked-by: Will Deacon <will@...nel.org>

Will