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

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Message-ID: <87qzvo3oef.ffs@tglx>
Date: Tue, 30 Sep 2025 00:05:44 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Peter Zijlstra <peterz@...radead.org>, Geert Uytterhoeven
 <geert@...ux-m68k.org>
Cc: 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 13:04, Peter Zijlstra wrote:
> 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?

Ooops.

Thanks for the quick fix!

       tglx