Re: [coreboot] [PATCH][v3] Check that CAR and ROM areas don'tcollide

[Corey Osgood]

On Wed, Dec 10, 2008 at 1:29 PM, Myles Watson  wrote:
> > -----Original Message-----
> > From: [e-mail] [mailto:
>
> [e-mail]]
> > On Behalf Of Carl-Daniel Hailfinger
> > Sent: Wednesday, December 10, 2008 11:18 AM
> > To: Corey Osgood
> > Cc: Segher Boessenkool; coreboot
> > Subject: Re: [coreboot] [PATCH][v3] Check that CAR and ROM areas
> > don'tcollide
> >
> > Hi Segher,
> >
> > is the last test below with 0x100000000 (2^32) in the formula guaranteed
> > to work or may cpp truncate the results to 32 bit? I'd rather avoid
> > introducing a test that can never trigger.
>
> ...snip...
> > What you actually want is this test:
> > #if CONFIG_CARBASE + CONFIG_CARSIZE + (CONFIG_COREBOOT_ROMSIZE_KB * 1024)
> > > 0x100000000
>
> To avoid that problem, maybe we should /1024 instead of *.
> #if CONFIG_CARBASE/1024 + CONFIG_CARSIZE/1024 + CONFIG_COREBOOT_ROMSIZE_KB
> >
>
> 1<<22
>
> I realize that 1<<22 isn't pretty, but the rest doesn't seem too bad.
>
> Thanks,
> Myles

I'm probably missing something, but I'm not seeing the off-by-one error in
the original function. CONFIG_CARBASE and 0xffffffff are both addresses, you
could say they're both off by one, but by comparing them the problem is
negated. You could rearrange it to

0xffffffff - (CONFIG_CARBASE + CONFIG_CARSIZE) < CONFIG_COREBOOT_ROMSIZE_KB
* 1024

which should, AFAIK, compare the remaining space with the ROM size. Right?

Thanks,
Corey