Re: gas on Mac OS X

[Martin Schaffner <schaffner at gmx dot li>]

On 21.04.2004, at 17:28, Ian Lance Taylor wrote:

> Martin Schaffner <schaffner@gmx.li> writes:
>
> Thanks for working on this.  I wish we could call the files macho
> instead of mach-o, but I guess that has a pronunciation problem.
>
> > * Indirect symbols. Mach-O supports so called "indirect symbols",
> > which  are something different than the indirect symbols of ELF. Is
> > there a  terminology to distinguish these two concepts? Maybe in gcc?
> > We could  call the ones in Mach-o "mach-o-indirect symbols"...
> > Anyway, to support these there has to be an interface between bfd and
> > gas. This design has to be carefully thought out. Maybe someone can
> > help me.
>
> Could you describe what Mach-O indirect symbols are?

Please read section "Indirect Addressing" of  
http://developer.apple.com/documentation/DeveloperTools/Conceptual/ 
MachORuntime/2rt_powerpc_abi/chapter_9_section_6.html

Myself, I have some problems understanding them. From the Apple doc I  
understand that it makes the last part of  
http://membres.lycos.fr/schaffner/prog/binutils/ 
indirect_symbols.tar.bz2 possible. But this also works on GNU/Linux...

I uploaded cctools to my homepage:
http://membres.lycos.fr/schaffner/prog/binutils/cctools-495.tar.bz2

> Note that as far as I know ELF does not have indirect symbols.  BFD
> supports indirect symbols because they are a GNU extension to the
> a.out object file format, essentially another of way of solving the
> problem which ELF weak defined symbols solve.  The ELF backend linker
> then uses BFD indirect symbols as part of the implementation of ELF
> versioned symbols.
>
> > * Weak references. These too are not the same thing as ELF's weak
> > symbols.
>
> Are they the same as ELF weak undefined symbols, though?

I don't know ELF weak undefined symbols.

Mach-O weak references tell the dynamic linker: Link this symbol if you  
find it, otherwise set it to null and continue. The program must then  
check if the symbol is null before using it. This feature is useful for  
selectively implementing features that may be available on some  
systems, but not on others.

Martin