linux-kernel - Re: [PATCH v2] init/Kconfig: fix CC_HAS_ASM_GOTO_TIED

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Message-ID: <Y3vSErWtH6L6GmMn@google.com>
Date:   Mon, 21 Nov 2022 19:31:30 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     alexandre.belloni@...tlin.com
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        linux-kbuild@...r.kernel.org
Subject: Re: [PATCH v2] init/Kconfig: fix CC_HAS_ASM_GOTO_TIED_OUTPUT test
 with dash

+Masahiro and build, as I don't think this should go through the KVM tree (which
is also partly why no one has responded).

On a related topic, should init/Kconfig be added to the KCONFIG MAINTAINERS entry?
Or is there a better owner for this?

diff --git a/MAINTAINERS b/MAINTAINERS
index 046ff06ff97f..ffff36e16b88 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -11040,6 +11040,7 @@ T:      git git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild.git
 F:     Documentation/kbuild/kconfig*
 F:     scripts/Kconfig.include
 F:     scripts/kconfig/
+F:     init/Kconfig
 
 KCOV
 R:     Dmitry Vyukov <dvyukov@...gle.com>

On Tue, Nov 15, 2022, alexandre.belloni@...tlin.com wrote:
> From: Alexandre Belloni <alexandre.belloni@...tlin.com>
> 
> When using dash as /bin/sh, the CC_HAS_ASM_GOTO_TIED_OUTPUT test fails
> with a syntax error which is not the one we are looking for:
> 
> <stdin>: In function ‘foo’:
> <stdin>:1:29: warning: missing terminating " character
> <stdin>:1:29: error: missing terminating " character
> <stdin>:2:5: error: expected ‘:’ before ‘+’ token
> <stdin>:2:7: warning: missing terminating " character
> <stdin>:2:7: error: missing terminating " character
> <stdin>:2:5: error: expected declaration or statement at end of input
> 
> Removing '\n' solves this.
> 
> Fixes: 1aa0e8b144b6 ("Kconfig: Add option for asm goto w/ tied outputs to workaround clang-13 bug")
> Signed-off-by: Alexandre Belloni <alexandre.belloni@...tlin.com>
> ---
>  init/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index 694f7c160c9c..13e93bcbc807 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -87,7 +87,7 @@ config CC_HAS_ASM_GOTO_OUTPUT
>  config CC_HAS_ASM_GOTO_TIED_OUTPUT
>  	depends on CC_HAS_ASM_GOTO_OUTPUT
>  	# Detect buggy gcc and clang, fixed in gcc-11 clang-14.
> -	def_bool $(success,echo 'int foo(int *x) { asm goto (".long (%l[bar]) - .\n": "+m"(*x) ::: bar); return *x; bar: return 0; }' | $CC -x c - -c -o /dev/null)
> +	def_bool $(success,echo 'int foo(int *x) { asm goto (".long (%l[bar]) - .": "+m"(*x) ::: bar); return *x; bar: return 0; }' | $CC -x c - -c -o /dev/null)

Tested a variety of compiler versions via godbolt, and the results are the same
for all cases, so with the caveat that I am far from a shell expert:

Reviewed-by: Sean Christopherson <seanjc@...gle.com>