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SubjectRe: PATCH - x86-64 signed-compare bug, was Re: select() setting ERESTARTNOHAND (514).
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
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