x86 LAHF indeterminated bits?

Emulation of old PCs, PC hardware, or PC peripherals.

x86 LAHF indeterminated bits?

Postby superfury » 2019-2-23 @ 12:15

What are the values of the indeterminate bits in AH after an LAHF? Are they always the sticky flags of the FLAGS register, all cleared, all set or are they all whatever was in AH before executing LAHF(so just modifying the defined bits that are documented in EFLAGS)?

So what's in AH bits 1,3,5 after LAHF? The bits that were there before(unmodified)? 1s? 0s? The stuck bits in the FLAGS register?

UniPCemu currently stores the stuck bits of (E)FLAGS there, which may be hardware-dependent.

Is that correct behaviour?
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Re: x86 LAHF indeterminated bits?

Postby peterferrie » 2019-2-27 @ 19:10

It's the regular bits, just like a PUSHF/POP AX/MOV AH,AL would produce.
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