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

[Corey Osgood]

On Wed, Dec 10, 2008 at 4:46 PM, Myles Watson  wrote:
> On Wed, Dec 10, 2008 at 2:27 PM, Carl-Daniel Hailfinger <
> [e-mail]> wrote:
> > On 10.12.2008 20:39, Corey Osgood wrote:
> > > 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 *
> > > > > > 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?
> > >
> >
> > Let me demonstrate the off-by-one error for you with your original code:
> >
> > #define CONFIG_CARBASE 0xffef0000
> > #define CONFIG_CARSIZE 0x00010000
> > #define CONFIG_COREBOOT_ROMSIZE_KB 1024
> > #if ((0xffffffff - (CONFIG_COREBOOT_ROMSIZE_KB * 1024)) < (CONFIG_CARBASE
> > CONFIG_CARSIZE))
> >
> > #error Your current Cache-As-Ram base does not allow room to map the
> > selected\
> >  chip size to memory. Please select a different chip size or move the CAR\
> >  base to another sane location.
> > #endif
> >
> > Try to compile that snippet. It will error out although the
> > configuration is valid.
> > CAR is from 0xffef0000-0xffefffff (size 0x10000)
> > ROM is from 0xfff00000-0xffffffff (size 0x100000)
> >
> > Regards,
> > Carl-Daniel
>
> I agree with Carl-Daniel.
>
> How about this one:
> #if ((0xffffffff - (CONFIG_COREBOOT_ROMSIZE_KB * 1024)) < (CONFIG_CARBASE +
> CONFIG_CARSIZE-1))
> if the last useable address before ROM < last CAR address (instead of next
> useable address after CAR)
>
> Thanks,
> Myles

Carl-Daniel, thanks, I see it now. Per Segher's email I'd prefer to go with
Carl-Daniel's original suggestion of using 0x100000000.

Thanks,
Corey