Re: nm not finding __objc_class names Re: Loading bundle resources using GNUstep runtime 2.0

[David Chisnall]

On 16/02/2020 20:42, Patryk Laurent wrote:
> I see the list “frameworkClasses” is meant to be populated during the make 
> process running “nm *.o -Pg” as part of EXTRACT_CLASS_NAMES_COMMAND. Defined in 
> target.make, this command is used to look for lines output from nm starting 
> with “__objc_class_name”.

I'm not sure why it would.  That's an implementation detail of the old 
ABI.  The v2 ABI[1] creates a `_OBJC_CLASS_{class name}` symbol for each 
class.  Note that this symbol should *never* be referenced directly, it 
exists solely for the indirection pointers in the `__objc_class_refs` 
section to point to to import the classes that are used.  The runtime is 
free to dynamically allocate a new class structure and to update 
pointers to reflect the new structure, giving forwards binary 
compatibility guarantees (a 2.2 ABI may add fields to the class 
structure and the runtime can then silently auto-update the 2.0 ABI 
requirements).

If all you want is to extract the names, that should be fine, just look 
for the new pattern.

Note that, if you want to enumerate all of the classes in a library, you 
can do so on ELF platforms by using dl_iterate_phdr to find the 
`__objc_classes` section in each loaded ELF image and collect the 
classes directly (this section is an array of pointers to classes 
declared in the ELF file).  This will work irrespective of build system goo.

On Windows, the corresponding section is `.objcrt$CLS` (though I believe 
the CLS part is a sub-section and is stripped during linkage).

David

[1] Documented here: 
https://github.com/gnustep/libobjc2/blob/master/ABIDoc/abi.tex