linux-kernel - Re: [patch V2a 2/6] kbuild: Disable CC_HAS_ASM_GOTO

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Message-ID: <20250929110400.GL3419281@noisy.programming.kicks-ass.net>
Date: Mon, 29 Sep 2025 13:04:00 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Nathan Chancellor <nathan@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.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: Re: [patch V2a 2/6] kbuild: Disable CC_HAS_ASM_GOTO_OUTPUT on clang
 < version 17

On Mon, Sep 29, 2025 at 12:58:14PM +0200, Geert Uytterhoeven wrote:
> On Mon, 29 Sept 2025 at 12:09, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Mon, Sep 29, 2025 at 11:38:17AM +0200, Geert Uytterhoeven wrote:
> >
> > > > +       # Detect buggy clang, fixed in clang-17
> > > > +       depends on $(success,echo 'void b(void **);void* c();int f(void){{asm goto("jmp %l0"::::l0);return 0;l0:return 1;}void *x __attribute__((cleanup(b))) = c();{asm goto("jmp %l0"::::l1);return 2;l1:return 1;}}' | $(CC) -x c - -c -o /dev/null)
> > >
> > > This is supposed to affect only clang builds, right?  I am using
> > > gcc version 13.3.0 (Ubuntu 13.3.0-6ubuntu2~24.04) to build for
> > > arm32/arm64/riscv, and thus have:
> > >
> > >     CONFIG_CC_IS_GCC=y
> > >
> > > Still, this commit causes
> > >
> > >     CONFIG_CC_HAS_ASM_GOTO_OUTPUT=y
> > >     CONFIG_CC_HAS_ASM_GOTO_TIED_OUTPUT=y
> > >
> > > to disappear from my configs? Is that expected?
> >
> > Not expected -- that means your GCC is somehow failing that test case.
> > Ideally some GCC person will investigate why this is so.
> 
> Oh, "jmp" is not a valid mnemonic on arm and riscv, and several other
> architectures...

Ah, d'0h indeed.

void b(void **);void* c();int f(void){{asm goto(""::::l0);return 0;l0:return 1;}void *x __attribute__((cleanup(b))) = c();{asm goto(""::::l1);return 2;l1:return 1;}}

Seems to still finger the issue on x86_64. That should build on !x86
too, right?