[U-Boot] [PATCH 0/2] Make sure 85xx bss doesn't start at 0x0

[Peter Tyser <ptyser@xes-inc.com>]

Hi Wolfgang,

> So far U-Boot is actually a 32 bit boot loader; address calculations
> like this "just wrap around". So far this has not caused problems yet;
> what has caused problems is that we can have overlapping sections on
> 4xx. Also it's probably overkill that each board has it's own linker
> script.

I added some debug and came to the same conclusion about the wrapping
math.

Full ack on the linker script consolidation.

> I would like to see this fixed in this process. Maybe Stefan finds
> some spare cycles to address this.
> 
> > > Where is BSS on 44x boards?  I dont see any reason we shouldn't be  
> > > able to put it at the same location.
> > 
> > >From the XPedite1000:
> > 
> >   [ 0]                   NULL            00000000 000000 000000 00      0   0  0
> >   [ 1] .resetvec         PROGBITS        fffffffc 03f2e4 000004 00  AX  0   0  1
> >   [ 2] .bootpg           PROGBITS        fffff000 03e2e8 000250 00  AX  0   0  1
> >   [ 3] .text             PROGBITS        fff80000 000094 0303b0 00  AX  0   0  4
> >   [ 4] .rodata           PROGBITS        fffb03b0 030444 00a14c 00   A  0   0  4
> >   [ 5] .reloc            PROGBITS        fffba500 03a594 002280 00  WA  0   0  4
> >   [ 6] .data             PROGBITS        fffbc780 03c814 00088c 00  WA  0   0  4
> >   [ 7] .data.rel.local   PROGBITS        fffbd00c 03d0a0 000a98 00  WA  0   0  4
> >   [ 8] .data.rel.ro.loca PROGBITS        fffbdaa4 03db38 0000b0 00  WA  0   0  4
> >   [ 9] .data.rel         PROGBITS        fffbdb54 03dbe8 000100 00  WA  0   0  4
> >   [10] .u_boot_cmd       PROGBITS        fffbdc54 03dce8 000600 00  WA  0   0  4
> >   [11] .bss              NOBITS          fffbe300 03e2e8 011c44 00  WA  0   0  4
> > 
> > I shied away from this for the 2 reasons above - the bootpg section will
> > be wiped out when the bss is cleared for images near their maximum size
> 
> I think it will not be needed any more by then.

Its not currently used (at least on 85xx), but I know using it had been
mentioned in the past.  There's a >3K chunk that's sitting empty right
now that could be used.  All things being equal I think it would be
ideal not to trash a section of U-Boot code - it could be useful and at
some point someone's going to be banging their head on the wall trying
to figure out why some chunk of assembly code isn't working.

> > If everyone is OK with the limitation of #1 above I can make the 85xx
> > act like the other PPC boards.  The only downside I see is that we could
> > never put any non-reset related code in the bootpg.
> 
> What about my suggestion to chose a fixed (random, non-zero) address?

I'd vote against this.  It'd have to be some area in low memory and
people would be bound to accidentally stomp on it and cause all sorts of
odd errors- like overwriting the exception vectors, but harder to debug.
I personally like the current implementation of putting the bss after
the entire U-Boot image.  It keeps U-Boot's code, malloc pool, stack,
bss, etc all in the same general area which is nice, and has the side
benefit that the bootpg won't be overwritten.

I know ORing in 0x10 is a bit ugly, but what's the real downside of
doing it?

Best,
Peter