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From: Andrew Morton <akpm@linux-foundation.org>
To: "yuan cooper" <yuanxjtu@hotmail.com>
Cc: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
	dmitry.torokhov@gmail.com
Subject: Re: About GCC4 Optimization
Date: Sat, 24 Mar 2007 20:31:18 -0800	[thread overview]
Message-ID: <20070324203118.3ab22ea4.akpm@linux-foundation.org> (raw)
In-Reply-To: <BAY144-F24481F006CCA5D5D74D6F4DF680@phx.gbl>

On Sun, 25 Mar 2007 03:42:25 +0000 "yuan cooper" <yuanxjtu@hotmail.com> wrote:

> Hi all:
>  
> during my work, I found there is a bug with GCC4 O2 optimization.
>  
> ---------------------
> float ftmp;
> unsigned long tmp;
> ftmp = 1.0/1024.0;
> tmp  = *(unsigned long *)(&ftmp);
> tmp  = (tmp >> 11) && 0xFFF;
> --------------------- 
>  
> if optimization level is O2, gcc will MOV eax to tmp, but current eax has a random value.
> -O is ok and gcc3 with O2 is ok too.
>  
>  
> I am a kernel newbie, I don't know how to make contributions to janitors, who will help me? It's my first post, any suggestion will be appreciated.

Don't use floating point in kernel code.  At all.

  parent reply	other threads:[~2007-03-25  4:31 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-03-25  3:32 keyboard.c: Stop flooding dmesg with useless warnings Parag Warudkar
2007-03-25  3:38 ` Parag Warudkar
     [not found]   ` <BAY144-F24481F006CCA5D5D74D6F4DF680@phx.gbl>
2007-03-25  4:28     ` About GCC4 Optimization Linus Torvalds
2007-03-25  5:07       ` David Schwartz
2007-03-25  4:31     ` Andrew Morton [this message]
2007-03-25  5:15   ` keyboard.c: Stop flooding dmesg with useless warnings Dmitry Torokhov
2007-03-25  5:27     ` Parag Warudkar
2007-03-25  5:29       ` Dmitry Torokhov
2007-03-25  5:35         ` Parag Warudkar
2007-03-25  9:16           ` Jiri Kosina
2007-03-25 14:32             ` Parag Warudkar

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