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Re: [Patch mach-o, indirect symbols 1/2] support indirect symbols in mach-o.

On 3 Jan 2012, at 16:17, Tristan Gingold wrote:
+	/* A pointer to the referenced symbol will be stored in the udata
+	   field.  Use that to find the string index.  */
+	s->symbol.value =
+	    ((bfd_mach_o_asymbol *)s->symbol.udata.p)->symbol.udata.i;

[ One issue is that we don't follow the BFD convention for indirect symbols. To be fixed later ]

that's a tricky one - we need the 'normal' symbols ahead of the indirects (so we'd have to swap in and out).

[ One question: does it make sense to output the indirect name here and therefore avoiding taking care of indirect symbols while sorting ? ]

I am not sure I follow the question - we are constrained to do things in a particular order by needing certain dependent information.

to construct and order the symtab - we need the sections.
to construct the indirect symbol dependent indices - we need the symbols sorted.

to construct the indirect symbol *value* we need the string table offset for the dependent symbol (which is only available when the symbol table is written). Note that this is academic when we write a dysymtab - since we don't then write 'bare' indirect symbols. If we do not write the dysymtab - then the 'normal' symbols precede the indirect ones which means that we get the *value* just in time.

I have just realized I misunderstood indirect symbols, simply because that's ambiguous.

well, maybe I have too ;-)
-- it's a weird scenario when there's a type that is not actually emitted - but is recognized.

There are two kinds of indirect symbols:

N_INDR symbols, which cannot be emitted by native as, and appear in the symbols table

they will not be emitted with the code I've applied [unless you disable the dysymtab], but intercepted and output as .indirect_symbols ...

.indirect_symbols, which never appear in the symbol table but only in the indirect symbols table.

... because I've used N_INDR as an intermediate representation for these ...

I think it would be better not to put .indirect_symbols in the symbol table, that would be clearer. Give me more time to think about that.

Then we'd have to introduce a new store with most of the properties of the symbols table, but restricted to .indirect_symbols ... there doesn't seem to be a particular penalty for using the symbol table (we could even use it with a zero name, like stabd does, if that would help -- the sort order is not determined on name).


N_INDR symbols _are_ recognized by the native "nm" ... which led me to deduce (possibly incorrectly) that the dysymtab way of doing things is simply a more efficient modern scheme than looking up from the name (which could be found from the old representation by the value field).

That is why I used N_INDR as an intermediate representation (from GAS).

I guess the alternative is to introduce another field into the symbol to carry the fact that they are of this type.


+ qsort (symbols, (size_t) nin, sizeof (void *), bfd_mach_o_cf_symbols);

[ Unfortunately qsort is not stable! ]

indeed, which is why there's a specific sort decider for each type - if you believe I've missed one (or that it's not adequate) then I guess we could switch to merge sort.

I think it is ok, but qsort is simply over-engineering. We simply need to separate local/external/undefined symbols.

.. well, to be compatible with the native tools we also have to sort undefined and global names into string order.


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