DOS ain't dead

NASM 0.98.39 (not full instruction support) ... LOADALL (Developers)

posted by Rugxulo , Usono, 31.03.2020, 20:07
(edited by Rugxulo on 31.03.2020, 20:43)

> But omitting CMPXCHG486, LOADALL, LOADALL286, SALC is bad because those were much more common!

I'm not a systems programmer, so I'm not familiar with all the gory details.

IIRC, it was claimed at one time that all 486 BIOSes emulated LOADALL, presumably for IBM's OS/2.

Wikipedia implies other software using it (MS Himem, Emm386, Smartdrv, Windows), or at least certain older versions (pre-XMS?). But no mention of it in Himemx nor JEMM386 sources.

Apparently it was removed in later processors, replaced by Pentium's RSM instruction (different encoding) for SMM (Systems Management Mode, aka ring -2). The actual encodings were reused instead for SYSCALL and SYSRET (both of which old NASM calls "P6" although Wikipedia says AMD64).

OS/2 Museum had a few things to say, too:

> On Intel processors, SYSCALL must be explicitly enabled and even then is
> only recognized in 64-bit mode, so it cannot possibly conflict with software
> written for the 286. On AMD processors, SYSCALL is not limited to 64-bit
> mode but must still be enabled via EFER.SCE, which again won’t be the case
> with software designed to run on 286s. Therefore SYSCALL does not conflict
> with 286 LOADALL emulation.

Strange stuff.

Complete thread:

• rebuilding NASM 0.98.39 (2005) for 16-bit 8086 host - Rugxulo, 14.03.2020, 08:13 (Developers)
  • rebuilding NASM 0.98.39 (2005) for 16-bit 8086 host - Rugxulo, 16.03.2020, 01:24
    • rebuilding NASM 0.98.39 (2005) for 16-bit 8086 host - rr, 16.03.2020, 15:22
      • rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - Rugxulo, 17.03.2020, 05:20
        • rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - ecm, 17.03.2020, 06:58
          • rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - Rugxulo, 22.03.2020, 00:48
            • rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - ecm, 22.03.2020, 10:13
              • rebuilding NASM 2.09 and NASM compatibility - ecm, 22.03.2020, 11:45
            • rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - ecm, 06.09.2020, 23:09
        • rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - Rugxulo, 22.03.2020, 00:42
          • rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - marcov, 22.03.2020, 13:08
            • CMOV - ecm, 22.03.2020, 14:26
              • CMOV - marcov, 22.03.2020, 18:32
                • CMOV - marcov, 23.03.2020, 12:52
            • rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - Rugxulo, 23.03.2020, 04:27
              • NASM 0.98.39 (MSC 7, "286", not full instruction support) - Rugxulo, 24.03.2020, 20:36
                • NASM 0.98.39 (not full instruction support) - Rugxulo, 24.03.2020, 21:16
                  • NASM 0.98.39 (not full instruction support) - ecm, 24.03.2020, 22:55
                    • NASM 0.98.39 (not full instruction support) - Rugxulo, 24.03.2020, 23:17
                  • NASM 0.98.39 (not full instruction support) ... LOADALL - Rugxulo, 31.03.2020, 20:07
              • rebuilding NASM 0.98.39 (without MMX/3DNOW/686/SSE) - Rugxulo, 13.04.2020, 07:16
            • deprecated MMX and obsolete 3DNow! - Rugxulo, 24.03.2020, 17:54