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Date:   Fri, 31 Aug 2018 22:01:36 +0200 (CEST)
From:   Thomas Gleixner <>
To:     Meelis Roos <>
cc:     Linux Kernel list <>,,
        Peter Zijlstra <>
Subject: Re: cmpxchg.h:245:2: error: ‘asm’ operand has impossible constraints

On Mon, 27 Aug 2018, Meelis Roos wrote:

> While trying to compile v4.18-13105-gaba16dc5cf93 with gcc 5.3.1 on a 
> 32-bit x86 configured for AMD K6:

I tried to get hold of that debian gcc 5.3.1 compiler, but no luck so far.

>   CC      mm/slub.o
> In file included from ./arch/x86/include/asm/atomic.h:8:0,
>                  from ./include/linux/atomic.h:7,
>                  from ./arch/x86/include/asm/thread_info.h:54,
>                  from ./include/linux/thread_info.h:38,
>                  from ./arch/x86/include/asm/preempt.h:7,
>                  from ./include/linux/preempt.h:81,
>                  from ./include/linux/spinlock.h:51,
>                  from ./include/linux/mmzone.h:8,
>                  from ./include/linux/gfp.h:6,
>                  from ./include/linux/mm.h:10,
>                  from mm/slub.c:13:
> mm/slub.c: In function ‘__slab_free’:
> ./arch/x86/include/asm/cmpxchg.h:245:2: error: ‘asm’ operand has impossible constraints
>   asm volatile(pfx "cmpxchg%c4b %2; sete %0"   \

I so love the informative output of GCC on ASM errors ....

What's even more confusing is that the __cmpxchg_double() macro has not
been changed since Jan, 2012.



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