On Tue, 2009-10-06 at 15:46 -0500, Kumar Gala wrote:
On Oct 6, 2009, at 1:08 PM, Peter Tyser wrote:
On Tue, 2009-10-06 at 19:51 +0200, Wolfgang Denk wrote:
Dear Peter Tyser,
In message 1254843932.24664.2083.camel@localhost.localdomain you wrote:
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.
OK, if you think so...
I know ORing in 0x10 is a bit ugly, but what's the real downside of doing it?
Nothing. I just hate to allocate the bss at 0x0, because this is actually incorrect - it's the result of an address overflow / truncation, and pretty much misleading to someone trying to read and understand the code. For the linked image, it does not _look_ as if the bss was located _after_ the U-Boot image, it looks detached and allocated in low RAM.
Do you have a preference Kumar? You're probably going to be the first in line to have to deal with any resulting confusion:)
I personally would rank the options:
- OR in an offset to the bss address and leave some good comments in
the linker script and commit message
- Make the bss the last section like other PPC boards which would
result in the bootpg sometimes being overwritten
- Put the bss at an arbitrary address
I don't have a preference, but maybe I missed the answer to my question about where does 44x put the BSS.
The 44x boards put the bss after "the rest" of u-boot, but before the bootpg section. Sometimes the bss might overlap the bootpg which would mean the bootpg would get zeroed out on bootup and the bss would "wrap around to 0 (which is fine, just confusing). Eg:
[ 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
Is it possible to put it before TEXTBASE?
I looked into that originally but couldn't get it to work via the linker script alone. If we wanted to hardcode a bss size, we could pass "-Tbss <TEXTBASE - HARDCODED_BSS_SIZE>" to ld to position it. We could allocate some relatively huge chunk of memory for it below TEXTBASE, but I'm not sure we could make it dynamically sized.
Peter