> Now my memory is a little hazy... I think OSF/1-386 used MachO originally,
> but I've forgotten. Switching the kernel to use ELF was one of the
> differences between OSF1 and Tru64 IIRC.
GEM never had to support Mach-O on any of its target platforms. DEC's
Unix on MIPS used COFF. Tru64 used ELF exclusively. I don't know
what Apple used for object files before OS X. IIRC NeXT was based on
the CMU MACH microkernel and hence used Mach-O. OS X is
FreeBSD-based, but it uses Mach-O.
OSF/1 on MIPS used ECOFF by default, but at least some versions could also create and run ELF executables. That was all early to mid 1992, I believe. I don't have my DECstation up right now to check but I'm sure that the OSF/1 2.0 beta can do it, and I wouldn't be surprised if the versions of 1.0 with the v3.0 compiler could also do it. I remember trying to do ELF shared libraries but I think that support wasn't ready yet, which is a shame because the ECOFF shared libraries on that platform are not fun to deal with. Not as bad as SGI's ECOFF shared libraries on IRIX 4 though. I'm not sure if anyone outside of SGI ever bothered to put in the work required to make one.
Wasn't OSF's original intent to use the OSF/ROSE object format?
-Henry