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SubjectRe: managing kallsyms_addresses
Robin Getz wrote:
> When the kernel needs to find out what symbol is at a specific address, it
> uses kallsyms_lookup() This seems to work pretty well - almost.
>
> The problem is today, we don't to remove the symbols from the init section
> when the init section is freed. There is invalid data in kallsyms_addresses.
> [...]
> There would be two solutions:
> - when freeing the init section, remove all the init labels from the
> kallsyms_addresses, and resort/pack it.

This should be doable, but to be worth it, we would need to use
different structures for the init symbols, that would be stored in
__initdata.

Then, ideally we would have separate functions in the __init section to
look up symbols in those structures that would only be called until we
released the init sections.

On the plus side, this would avoid the "repacking" the kallsyms
structures to remove the init labels.

> - if the init section is unloaded, have is_kernel_inittext always return 0.

This is by far the simplest solution. I even STR a patch floating around
to do this, by I can't seem to locate it now... :(

> I assume that similar things need to be handled for module init too, but I
> have not run into that yet.

It seems that at least the last solution should be easy enough to
implement there.

> Thoughts?

I think that the simplest solution (the second one) is probably the best
for now.

One thing that did cross my mind though, is stuff like lockdep.

If we run a locking sequence that is called from init code, and later a
different locking sequence is used when we already freed init data, how
can the debug information show the names of the functions that generated
the previous locking sequence?

It seems that the only "correct" approach would be to store a "before
freeing init sections" flag together with the function pointer, and then
have a kallsyms interface that could receive this flag to know where to
look.

In that case, the first solution can not be used at all (because we need
to keep the init symbols anyway) and the second solution could be simply
implemented by having a default value for the flag that is the "current
state" for that flag...

--
Paulo Marques - www.grupopie.com

"There cannot be a crisis today; my schedule is already full."


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