linux-kernel - Re: 2.4.x: i386/x86

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Date:	Mon, 09 Oct 2006 08:27:54 +0200
From:	Jan Kiszka <jan.kiszka@....de>
To:	Willy Tarreau <w@....eu>
CC:	linux-kernel@...r.kernel.org
Subject: Re: 2.4.x: i386/x86_64 bitops clobberings

Willy Tarreau wrote:
> I've done it too, but unfortunately, I discovered that it does not build
> with gcc-2.95 anymore, while 3.3 is fine :
> 
> cyclades.c: In function `cyy_interrupt':
> /usr/src/git/linux-2.4/include/asm/bitops.h:130: inconsistent operand constraints in an `asm'
> cyclades.c: In function `cyz_handle_rx':
> /usr/src/git/linux-2.4/include/asm/bitops.h:130: inconsistent operand constraints in an `asm'
> 
> 127        __asm__ __volatile__( LOCK_PREFIX
> 128                "btsl %2,%1\n\tsbbl %0,%0"
> 129                :"=r" (oldbit),"+m" (ADDR)
> 130                :"Ir" (nr) : "memory");
> 
> 
> I don't know what the right solution should be. I'm not fond of #ifdefs,
> and I'm embarrassed to know that gcc can do all sorts of nasty things due
> to a wrong clobbering :-/
> 
> If you have any idea on the subject, I'm willing to try.

What about

#if __GNUC__ < 3
#define ADDR_DEPS "=m"
#else
#define ADDR_DEPS "+m"
#endif

	__asm__ __volatile__( LOCK_PREFIX
		"btsl %2,%1\n\tsbbl %0,%0"
		:"=r" (oldbit),ADDR_DEPS (ADDR)
		:"Ir" (nr) : "memory");

or something similar? Would keep the number of #ifs low.

Jan


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