SBC HL,rr writes its result to A instead of HL
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- Dominant language
- Python
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- 12
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Description
In Z80IL.py, OP.SBC computes the subtraction at the operand size but always stores to A as one byte:
tmp = il.sub_borrow(size, lhs, rhs, il.flag("c"), flags="*")
tmp = il.set_reg(1, "A", tmp)
So ed 42 (SBC HL,BC) lifts as A = sbb.w{*}(HL, BC, flag:c) and the 16-bit result never reaches HL.
16-bit compare/subtract is common, so this silently drops pointer arithmetic — 39 sites in one test binary. Example: AND A / SBC HL,BC / LD A,(HL).
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Research direction
Start in Z80IL.py at OP.SBC and inspect how the destination register is selected for each operand size. Reproduce the ed 42 example and verify that SBC HL,BC produces a 16-bit result in HL while the existing 8-bit behavior remains correct.
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Assessment
- Tech stack
- python
- Domain
- reverse-engineering
- Issue type
- Bug
- Difficulty
- 2/5
- Estimated time
- 1-3 hours
- Activity status
- Quiet
- Clarity
- Clearly specified
- Newbie friendliness
- 74/100