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
FWIW, I think an arbitrary address disjoint from the u-boot addresses is best. While u-boot is in ROM, you can't use the bss anyway. The bss will actually be located at an address selected by the u-boot code itself after memory is sized. All references to the bss will be re-located by subtracting the arbitrary start address and adding the run-time chosen start address. So the linked start address is not important, except that is cannot be NULL or it may confuse the relocation code that doesn't want to re-locate NULL pointers. Some of the confusion in this discussion probably stems from the fact that the linker scripts make the bss look like "part of u-boot", when it is really not. It is just a chunk of "zero'ed" ram, located anywhere the u-boot code decides to put it. An arbitrary strange address would make this more apparent.
Best Regards, Bill Campbell
Best, Peter
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