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    SubjectRe: managing kallsyms_addresses
    On Thu 31 Jan 2008 12:27, Paulo Marques pondered:
    > 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.

    I think this would be a good long term thing, but would require restructuring
    of all the kallsyms scripts, as well as everything in the kernel...

    > > - 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 can put something together if Rusty agrees this is the way to go.

    > > 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.

    Hmmm - I would need to defer to Ingo to understand the dependencies in lockdep
    and init labels/addresses in kallsyms_addresses.

    > 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?

    Maybe the lockdep needs to keep track of the label, not the address.

    > 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...

    That seems a little cumbersome to me...


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