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From: Neil Brown <neilb@suse.de>
To: Andi Kleen <ak@suse.de>
Cc: Neil Brown <neilb@suse.de>, Sean Reifschneider <jafo@tummy.com>,
	linux-kernel@vger.kernel.org
Subject: Re: PATCH - x86-64 signed-compare bug, was Re: select() setting ERESTARTNOHAND (514).
Date: Thu, 11 Jan 2007 12:02:53 +1100	[thread overview]
Message-ID: <17829.36029.240912.274302@notabene.brown> (raw)
In-Reply-To: message from Andi Kleen on Thursday January 11

On Thursday January 11, ak@suse.de wrote:
> > Just a 'me too' at this point. 
> > The X server on my shiny new notebook (Core 2 Duo) occasionally dies
> > with 'select' repeatedly returning ERESTARTNOHAND.  It is most
> > annoying!
> 
> Normally it should be only visible in strace. Did you see it without
> strace?

No, only in strace.

> 
> > 
> > You don't mention in the Email which kernel version you use but I see
> > from the web page you reference it is 2.6.19.1.  I'm using
> > 2.6.18.something.
> > 
> > I thought I'd have a quick look at the code, comparing i386 to x86-64
> > and guess what I found.....
> > 
> > On x86-64, regs->rax is "unsigned long", so the following is
> > needed....
> 
> regs->rax is unsigned long.
> I don't think your patch will make any difference. What do you think
> it will change?

If regs->rax is unsigned long, then I would think the compiler would
be allowed to convert

   switch (regs->rax) {
	case -514 : whatever;
   }

to a no-op, as regs->rax will never have a negative value.

However it appears that the current compiler doesn't make that
optimisation so I guess I was too hasty.

Still, I think it would be safer to have the cast, in case the compiler
decided to be clever.... or does the C standard ensure against that?

Sorry for the noise,

NeilBrown

  reply	other threads:[~2007-01-11  1:03 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-10 23:42 Sean Reifschneider
2007-01-11  0:27 ` David Miller
2007-01-11  1:04   ` Sean Reifschneider
2007-01-11  1:15     ` David Miller
2007-01-11  8:25       ` Sean Reifschneider
2007-01-11 22:22         ` bert hubert
2007-01-24  0:50           ` Sean Reifschneider
2007-01-11  0:37 ` PATCH - x86-64 signed-compare bug, was " Neil Brown
2007-01-11  0:40   ` Andi Kleen
2007-01-11  1:02     ` Neil Brown [this message]
2007-01-11  1:37       ` Andi Kleen
2007-01-11  4:09       ` Sean Reifschneider
2007-01-11 19:38       ` Denis Vlasenko
2007-01-11  0:43   ` David Miller

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