Debugging ld.so in gdb

[Florian Weimer]

* Jacob Kroon:

>> What I find really confusing is that this is not the result of a dlopen
>> call.  I definitely would expect that the maps array contains *all*
>> objects that are being loaded.  Clearly this is not the case here.
>> Somehow certain objects are missing, and then they get written into the
>> rpo array.
>> 
>> Please try to find libjvm.so among the l_initfini arrays of the objects.
>
> I do find libjvm.so in a couple of the maps[]->l_initfini[]->l_name
> arrays, yes.

Okay, and of course there is an assumption that those make it to the
maps.  No wonder we run off the array.

>> It must be present somewhere.  I assume it's also on the main list,
>> which starts off at _rtld_global._dl_ns[0]._ns_loaded.
>
> Hmm how do I iterate over that data structure ?
>
> See below:
>> (gdb) print _rtld_global._dl_ns[0]._ns_loaded[0]->l_name
>> $186 = 0x7ffff7ff1d97 ""
>> (gdb) print _rtld_global._dl_ns[0]._ns_loaded[1]->l_name
>> $187 = 0x0
>> (gdb) print _rtld_global._dl_ns[0]._ns_loaded[2]->l_name
>> $188 = 0x0
>> (gdb) print _rtld_global._dl_ns[0]._ns_loaded->l_name
>> $189 = 0x7ffff7ff1d97 ""
>> (gdb) print _rtld_global._dl_ns[1]._ns_loaded->l_name
>> Cannot access memory at address 0x8
>> (gdb) print _rtld_global._dl_ns[2]._ns_loaded->l_name
>> Cannot access memory at address 0x8

It's a list chained by l_prev/l_next.

Thanks,
Florian