On Mon, Jan 13, 2020 at 1:04 PM Clem Cole wrote: > @ Rico I'm failing sure ELF came from AT&T Summit, not Sun. > yes, but unless my memory is playing tricks, SunOS a.out had this feature. > @ Steve Johnson were you the manager when was created or were you folks > still using COFF? > > Anyway... There were issues with COFF WRT being > architecture-independent and supporting dynamic loading well. Steve Rago > would also be a good person to ask if you want some of the details. At one > point there was a COFF2 document, but it may have been System Vx licenses > only. Also, one of the issues was that AT&T had officially tied up COFF > as a proprietary format -- all part of the 'consider it standard' trying to > force their lunch down all the other UNIX systems throat which was not > having it. As a result, CMU's MachO was about to become the default > format (OSF and Apple were already using it for that reason), and Unix > International stepped in and convinced AT&T to released the ELF documents > (I was on the UI technical board at that point). I'm not sure how/why OSF > decided to back off, maybe because after ELF became public it got supported > by GCC. > > 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. > > On Mon, Jan 13, 2020 at 3:47 PM Rico Pajarola wrote: > >> This seems to have originated with SunOS 4. I believe a good proxy for >> finding anything that inherited from or was inspired by this is a linker >> that recognizes LD_PRELOAD. I wonder if there are other independent >> implementations in the Unix space. >> >> >> On Mon, Jan 13, 2020 at 11:59 AM Paul Winalski >> wrote: >> >>> The Executable and Linkable Format (ELF) is the modern standard for >>> object files in Unix and Unix-like OSes (e.g., Linux), and even for >>> OpenVMS. LInux, AIX and probably other implementations of ELF have a >>> feature in the runtime loader called symbol preemption. When loading >>> a shared library, the runtime loader examines the library's symbol >>> table. If there is a global symbol with default visibility, and a >>> value for that symbol has already been loaded, all references to the >>> symbol in the library being loaded are rebound to the existing >>> definition. The existing value thus preempts the definition in the >>> library. >>> >>> I'm curious about the history of symbol preemption. It does not exist >>> in other implementations of shared libraries, such as IBM OS/370 and >>> its descendants, OpenVMS, and Microsoft Windows NT. ELF apparently >>> was designed in the mid-1990s. I have found a copy of the System V >>> Application Binary Interface from April 2001 that describes symbol >>> preemption in the section on the ELF symbol table. >>> >>> When was symbol preemption when loading shared objects first >>> implemented in Unix? Are there versions of Unix that don't do symbol >>> preemption? >>> >>> -Paul W. >>> >>