Dear Peter Tyser,
In message 1254839043.24664.1890.camel@localhost.localdomain you wrote:
But bss is NOLOAD, and the actual location in the flash is just a fiction - we never use anything of this but the start address.
My concern was that we use __bss_start and _end to calculate the size of the bss to zero out. If the bss wraps, I'd be concerned about what gets cleared as _end would be truncated to a low memory address while __bss_start would be a high memory address. Or other similar problems - I didn't investigate what would really happen, I was just worried what could happen:)
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 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.
and I wasn't sure if there were any ramifications about the bss wrapping around to 0. Other arches must have a similar issue which would somewhat imply:
- No one cares if their bootpg/reset vector is cleared
I think this is only relevant while running from flash, but not after relocation.
- U-Boot works even if the bss wraps around to 0.
This is indeed the case.
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?
Best regards,
Wolfgang Denk