Re: Initial MIPS patch for Gold

[Ian Lance Taylor <iant at google dot com>]

Aleksandar Simeonov <Aleksandar.Simeonov@RT-RK.com> writes:

>>> +  target->fix_sections(this, symtab);
>> 
>> fix_sections is not a good name, since it doesn't say anything about
>> when the function is called or what it can do.  More seriously, when I
>> look at the implementation of fix_sections, I don't see anything that
>> can't be done in finalize_sections.  Why not just use finalize_sections?
>
> Problem here is that MIPS version of Gold needs some data that are not
> available in the moment when finalize_sections is executed. For example,
> number of elements in dynamic symbol table is needed for MIPS_SYMTABNO
> tag in .dynamic section , but it is known only after
> create_dynamic_symtab function is executed, so I added additional
> function that is called almost at the end of Layout::finalize, when all
> needed data is known.

Oh, I see.  You are using passing a pointer to Output_data_dynamic, and
then filling in the pointer later.  I don't particularly like that
approach, because it introduces a dependency which I think is unclear.
Nothing will notice if the linker changes such that the dynamic tag
value is written out before it is set.

The name add_special is not good, because it does not convey any
meaning--every value is special in its own way.  Instead, perhaps
add_target_specific--see the existing method of that name in
Output_data_reloc.  And implement it the same way that
add_target_specific is implemented: the code calls the target to get the
value, rather than simply trusting that the value has appeared in a
memory location; look for TARGET_CODE.

I note that for DT_MIPS_GOTSYM you are traversing the symbol table.
Traversing the symbol table is the single slowest operation in the
linker, and traversals should be avoided whenever possible.  As far as I
can tell you are just looking for the smallest dynamic symbol table
index.  The layout code already computes that, in
Layout::create_dynamic_symtab.  In this case you should just change the
Layout code to remember that number, and then retrieve it when you need
it.

Ian