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[ELF] symbol sets handling [2]

Ian Lance Taylor ian@airs.com
Sat Feb 8 22:16:00 GMT 2003 
Fabio Alemagna <falemagn@studenti.unina.it> writes:

> >  For that matter, what are
> > you trying to sort?  Do you want to sort a collection of symbol set
> > sections?  If so, why?
> 
> Yes, I want to do that, and the reason is that I do it right now, but with
> the help of a post processor which automatically builds a ld script and
> feeds it to ld. The reason for I want to have sortable symbol sets is that
> there are many occasions in which this is needed, basically all
> sistuations in which one needs to have a collection os symbols which have
> to be processed in a certain order. The AROS libc, for example, has
> initialization routines which need to be called upon program startup in a
> well defined order, and need to be called on program exiting in the
> opposite order, and the same goes for the list of libraries to open, which
> need to be opened in a well defined order.

You say that you do want to sort a collection of symbol set sections,
but your examples appear to be ones of sorting symbols within a single
symbol set section.

Consider:
    symbol set I
        symbol d
        symbol e
        symbol f
    symbol set II
        symbol x
        symbol y
        symbol z

Do you want to control the order of symbol set I and symbol set
II--e.g., arrange for symbol set II to appear before symbol set I?  Or
do you want to control the order of the symbols within the symbol
sets--e.g., arrange for f to precede d and/or z to precede x?

For the rest of this note I assume you want the latter sort of
control.

Have you considered not relying on the linker to do the sorting, but
to have each symbol in the set be the address of a structure
containing the priority and the function to call?  Then you can sort
the symbols in the correct order before you call them; inelegant but
simple.

If you must do it in the linker, then I suppose you are on the right
track by putting the priority into the section name, but you will need
to have some way for the linker to detect that it should emit the
__start and __stop symbols.  For example, you could invent some code
to be embedded in the section name, e.g.
    .gnu_symbol_set.NAME.PRIORITY
When the emulation sees a section of that names, it groups them,
sorted by priority (simpler if this can be done lexically) and emits
the __start and __stop symbols using NAME.

Ian
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