I have been looking into umov and as MSVC6 does not support umov in __asm blocks I need to figure out what to emit to do umov eax, 1, looking at https://en.wikipedia.org/wiki/X86_instruction_listings it has umov as such as 0F 1X /r, but I a, unclear as to what /r is.
I guess Intel have repurposed things as MSVC6 thinks 0F 13 is an SSE operation.
Last edited by red-ray on 2025-04-23, 08:10. Edited 2 times in total.
It does not look like that instruction can be encoded using an immediate as source
Thank you, I was hoping to use umov to tell if a CPU without CPUID is AMD or Intel as https://www.ardent-tool.com/CPU/486_Step.html says Intel 486 don't have umov and AMD do, however as you can see below my DX/33 SX729 seems to have it. I wonder if NT 4.00 catches the trap and fixes it up. I will see what happens on other i486.
I think the best I can do is deduce Intel if it does fail. It will also fail on Cyrix, but the umov code won't get used as SIV will have already figured out it's Cyrix.
The plot thickens, I checked what happens with my SX/33 SX797 and the umov is effectively a nop as eax does not change!
Clearly we need to see what happens on several other CPUs so I have attached the SIV32L V5.81 UMOV-04 test SIV.
If you have a i486 system with am AMD or Intel CPU that does not support CPUID please do SIV32L -DBGCPU > SIV_DBGOUT.log | MORE and post what get's logged in SIV_DBGOUT.log and exactly which CPU you have, for me it's:
1CPU Name and S-Spec CPUID SIV_DBGOUT.log output 2Intel DX/33 SX729 SIV32L umov eax, ecx - eax = 00000001 3Intel DX/33 SX810 Y SIV32L umov eax, ecx - eax = 00000001 4Intel DX2/50 SX954 Y SIV32L umov eax, ecx - eax = 00000001 - labelled as SX807 so a fake 5Intel DX4/100 SX900 Y SIV32L umov eax, ecx - eax = 00000001 6Intel SX/33 SX797 Y SIV32L umov eax, ecx - eax = 87654321 7Intel SX2/50 SX845 Y SIV32L umov eax, ecx - eax = 87654321 8Intel POD83 SU014 Y SIV32L umov eax, ecx - exception 9Cyrix 5x86-S-WT (M1sc) SIV32L umov eax, ecx - exception 10AMD Am486 DX2 Model 3 SIV32L umov eax, ecx - eax = 00000001 11AMD Am5x86 Mod E S 4 Y SIV32L umov eax, ecx - eax = 87654321 - Model E Stepping 4
This can be done on either Windows 9x or NT. Note: most of my i486 do have CPUID so I built a special SIV version so they would execute the umov.
Last edited by red-ray on 2025-04-14, 22:11. Edited 11 times in total.
