From: Richard Henderson <rth@twiddle.net>
To: Michal Moskal <malekith@pld.org.pl>
Cc: torvalds@transmeta.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] gcc-3.1 ffs problem, kernel 2.4.18
Date: Tue, 2 Apr 2002 14:59:55 -0800 [thread overview]
Message-ID: <20020402145955.A12932@twiddle.net> (raw)
In-Reply-To: <20020320174238.GA13533@ep09.kernel.pl> <20020328211025.A30037@twiddle.net> <20020329115731.GA3227@ep09.kernel.pl> <20020329144232.A495@twiddle.net> <20020402114848.GA9004@ep09.kernel.pl>
On Tue, Apr 02, 2002 at 01:48:48PM +0200, Michal Moskal wrote:
> Could you please check if it compiles for you?
Ah, I see the bug. I was looking at ffz (which is correct),
not ffs (which isn't).
> __asm__("bsfl %1,%0\n\t"
> "jnz 1f\n\t"
> "movl $-1,%0\n"
> "1:" : "=r" (r) : "g" (x));
The problem is ^^^
That sez any of register, memory, or immediate is ok.
It should be "r" instead, just like in ffz.
That said, we should probably be using __builtin_ffs
instead. The compiler knows how to do bsfl plus the
adjustment. Plus, it knows how to evaluate it at
compile-time for constants.
r~
next prev parent reply other threads:[~2002-04-02 23:00 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-03-20 17:42 [PATCH] gcc-3.1 ffs problem, kernel 2.4.18 Michal Moskal
2002-03-29 5:10 ` Richard Henderson
[not found] ` <20020329115731.GA3227@ep09.kernel.pl>
[not found] ` <20020329144232.A495@twiddle.net>
[not found] ` <20020402114848.GA9004@ep09.kernel.pl>
2002-04-02 22:59 ` Richard Henderson [this message]
2002-04-03 0:04 ` Linus Torvalds
2002-04-03 11:00 ` Richard Henderson
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