linux-kernel - [patch V2 2/6] kbuild: Disable asm goto on clang

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Message-ID: <20250916163252.100835216@linutronix.de>
Date: Tue, 16 Sep 2025 18:33:11 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
 Peter Zijlstra <peterz@...radead.org>,
 Nathan Chancellor <nathan@...nel.org>,
 kernel test robot <lkp@...el.com>,
 Russell King <linux@...linux.org.uk>,
 linux-arm-kernel@...ts.infradead.org,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Darren Hart <dvhart@...radead.org>,
 Davidlohr Bueso <dave@...olabs.net>,
 André Almeida <andrealmeid@...lia.com>,
 x86@...nel.org,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>,
 Jan Kara <jack@...e.cz>,
 linux-fsdevel@...r.kernel.org
Subject: [patch V2 2/6] kbuild: Disable asm goto on clang < 17

clang < 17 fails to use scope local labels with asm goto:

     {
     	__label__ local_lbl;
	...
	unsafe_get_user(uval, uaddr, local_lbl);
	...
	return 0;
	local_lbl:
		return -EFAULT;
     }

when two such scopes exist in the same function:

  error: cannot jump from this asm goto statement to one of its possible targets

That prevents using local labels for a cleanup based user access mechanism.

As there is no way to provide a simple test case for the 'depends on' test
in Kconfig, mark ASM goto broken on clang versions < 17 to get this road
block out of the way.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Nathan Chancellor <nathan@...nel.org>
---
V2: New patch
---
 init/Kconfig |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/init/Kconfig
+++ b/init/Kconfig
@@ -96,9 +96,14 @@ config GCC_ASM_GOTO_OUTPUT_BROKEN
 	default y if GCC_VERSION >= 120000 && GCC_VERSION < 120400
 	default y if GCC_VERSION >= 130000 && GCC_VERSION < 130300
 
+config CLANG_ASM_GOTO_OUTPUT_BROKEN
+	bool
+	depends on CC_IS_CLANG
+	default y if CLANG_VERSION < 170000
+
 config CC_HAS_ASM_GOTO_OUTPUT
 	def_bool y
-	depends on !GCC_ASM_GOTO_OUTPUT_BROKEN
+	depends on !GCC_ASM_GOTO_OUTPUT_BROKEN && !CLANG_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