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OpcodeDispatcher: Mark CF as being possibly set after inverting #4163

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OpcodeDispatcher: Mark CF as being possibly set after inverting #4163

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a69135c
OpcodeDispatcher: Mark CF as being possibly set after inverting
bylaws Nov 17, 2024
6baad30
unittests: Add test for carry inversion bug
bylaws Nov 17, 2024
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1 change: 1 addition & 0 deletions FEXCore/Source/Interface/Core/OpcodeDispatcher.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1730,6 +1730,7 @@ class OpDispatchBuilder final : public IREmitter {
}

CFInverted ^= true;
PossiblySetNZCVBits |= 1u << IndexNZCV(FEXCore::X86State::RFLAG_CF_RAW_LOC);
}

LOGMAN_THROW_AA_FMT(CFInverted == RequiredInvert, "post condition");
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27 changes: 27 additions & 0 deletions unittests/32Bit_ASM/FEX_bugs/InvertedCarrySet.asm
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@@ -0,0 +1,27 @@
%ifdef CONFIG
{
"RegData": {
"RAX": "1"
},
"Mode": "32BIT"
}
%endif

; FEX had a bug where inverting CF to match the ABI when flushing the register cache didn't mark CF as possibly being set.
; This caused accesses relying on that flag to be set correctly to return wrong values.

mov esp, 0xe0000020
mov al, 3
mov cl, 2
mov ecx, 1
mov eax, 1

and al, cl ; Zeros CF, non-inverted
push ecx ; Triggers a register cache flush
inc eax ; Tries to preserve CF, but would encounter the bug and set it instead
jnb succ
mov eax, 0
hlt
succ:
mov eax, 1
hlt
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