Re: [PATCH v2 5/6] Eliminate CONFIG_CC_HAS_ASM_GOTO_TIED_OUTPUT

From: Nicolas Schier <nsc@kernel.org>
To: Nathan Chancellor <nathan@kernel.org>
Cc: Julian Braha <julianbraha@gmail.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Bill Wendling <morbo@google.com>,
	Justin Stitt <justinstitt@google.com>,
	Arnd Bergmann <arnd@arndb.de>, Kees Cook <kees@kernel.org>,
	linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org,
	llvm@lists.linux.dev,
	Linus Torvalds <torvalds@linuxfoundation.org>,
	Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Charlie Jenkins <thecharlesjenkins@gmail.com>,
	Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	linux-riscv@lists.infradead.org
Subject: Re: [PATCH v2 5/6] Eliminate CONFIG_CC_HAS_ASM_GOTO_TIED_OUTPUT
Date: Thu, 12 Nov 2026 12:34:50 +0100	[thread overview]
Message-ID: <avWkWm1N5rv52GG4@levanger> (raw)
In-Reply-To: <20261111-kconfig-toolchain-updates-v2-5-b2d9415c1757@kernel.org>

On Wed, Nov 11, 2026 at 05:52:07PM -0700, Nathan Chancellor wrote:
> Commit 1aa0e8b144b6 ("Kconfig: Add option for asm goto w/ tied outputs
> to workaround clang-13 bug") added CONFIG_CC_HAS_ASM_GOTO_TIED_OUTPUT to
> avoid a bug in clang's asm goto with outputs support when a tied output
> was used. The fix in clang was to match GCC's documented behavior.
> 
> Now that the minimum supported version of clang has long been bumped
> past the version where the fix landed (clang-14), any compiler that
> satisfies the dependencies of CONFIG_CC_HAS_ASM_GOTO_OUTPUT will support
> tied outputs properly. Eliminate CONFIG_CC_HAS_ASM_GOTO_TIED_OUTPUT in
> favor of just checking for CONFIG_CC_HAS_ASM_GOTO_OUTPUT directly.
> 
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---

[...]
> diff --git a/scripts/Kconfig.toolchain b/scripts/Kconfig.toolchain
> index 6520a06a9103..9454ef5294d5 100644
> --- a/scripts/Kconfig.toolchain
> +++ b/scripts/Kconfig.toolchain
> @@ -120,11 +120,6 @@ config CC_HAS_ASM_GOTO_OUTPUT
>  	depends on !GCC_ASM_GOTO_OUTPUT_BROKEN
>  	depends on $(success,echo 'int foo(int x) { asm goto ("": "=r"(x) ::: bar); return x; bar: return 0; }' | $(CC) -x c - -c -o /dev/null)
>  
> -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]) - .": "+m"(*x) ::: bar); return *x; bar: return 0; }' | $CC -x c - -c -o /dev/null)

The comments reads as if gcc 8 to 10 are affected.  Is the comment
somehow misleading, or should we still keep this until gcc-10 is the
minimum gcc version?

-- 
Nicolas