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bdshemu: Fix MOVS/STOS/LODS/SCAS/CMPS silent no-op at MaxInstructionsCount boundary #116

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Merged
vlutas merged 1 commit into from
Jun 29, 2026
Merged

bdshemu: Fix MOVS/STOS/LODS/SCAS/CMPS silent no-op at MaxInstructionsCount boundary #116

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12 changes: 7 additions & 5 deletions bdshemu/bdshemu_x86.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2640,8 +2640,9 @@ ShemuX86Emulate(
case ND_INS_LODS:
case ND_INS_STOS:
case ND_INS_MOVS:
// Fetch the rCX register, which is the third operand in case of repeated instructions.
while (Context->InstructionsCount < Context->MaxInstructionsCount)
// do/while: outer loop already gated this dispatch on a budget slot,
// so iteration #1 must run even at MaxInstructionsCount == 1.
do
{
// Get the RCX value.
GET_OP(Context, 2, &dst);
Expand All @@ -2667,12 +2668,13 @@ ShemuX86Emulate(
}

Context->InstructionsCount++;
}
} while (Context->InstructionsCount < Context->MaxInstructionsCount);
break;

case ND_INS_SCAS:
case ND_INS_CMPS:
while (Context->InstructionsCount < Context->MaxInstructionsCount)
// Same budget contract as MOVS above.
do
{
// Get the RCX value.
GET_OP(Context, 2, &dst);
Expand Down Expand Up @@ -2717,7 +2719,7 @@ ShemuX86Emulate(
}

Context->InstructionsCount++;
}
} while (Context->InstructionsCount < Context->MaxInstructionsCount);
break;

case ND_INS_MUL:
Expand Down
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