[U-Boot-Users] u-boot BOOTELF clearing SHT_NOBITS sections

[Mike Frysinger]

On Sunday 04 May 2008, Baruch Cochavy wrote:
> u-boot's bootelf clears (memset to 0) sections of SHT_NOBITS type. This
> covers .bss sections - however, it might also includes other sections,
> not expected to be cleared as per some users expectations (stacks, for
> example).

most people dont declare sections for stacks.  i dont think ive ever seen an 
ELF that does it.

> I am beginning to wonder if this behavior is correct/desired: if one
> tries to bootelf an ELF file which happens to resizde somewhere inside
> the .bss section, or some other data section of the loaded code, bootelf
> clears it (or part of it...) while loading, corrupting the code to be
> loaded.

if you have overlapping sections, then your ELF is broken.  if you have data 
in the middle of the .bss, then it isnt a NOBITS by definition, it's 
PROGBITS.  you're describing invalid scenarios.

> AFAIK, .bss is normally zeroed out in crt0 (or equivalent), so there is
> no need (?) to zero it in bootelf. Bootelf may also defer all such
> actions (clearing section) to the end of the loading process.

there is no normal sense here.  the only real guarantee is that when main() 
starts executing, the C runtime environment is entirely valid (or any 
pre-main initializers that get run).  by dropping the behavior in question, 
you'd be breaking things that are working today, so it's pretty hard to 
change it at all.

really though, using the section headers is going to always lead to 
conflicting needs.  the program headers should be used instead ... perhaps a 
new command (or option) can be added for it ...
-mike
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