where do undefined symbols get resolved?

[Doug Evans]

Doug Evans writes:
 > Would someone mind pointing me to the source for the code that
 > resolves undefined symbols?
 > 
 > target = elf
 > 
 > input = foo.o --just-symbols=foo2.elf
 > 
 > foo.o has an undefined symbol that is resolved by foo2.elf
 > which is a fully linked executable.
 > 
 > Where in the linker or bfd sources is the code that resolves
 > the undefined symbol?  i.e. the actual line that says, figuratively,
 > 
 >    undefined_symbol->value = x;

Ugh, I think I worded that badly.  Sorry.

I think I've got a linker bug.  A symbol isn't being resolved that
should be resolved.  I'm trying to find the code that loops
over undefined symbols and tries to look up each's value.
I'm guessing that lookup is failing somehow.