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Track both previous and current opcode in the analysis loop to handle edge cases where opcodes with immediates (SWAPN, DUPN, EXCHANGE) have their immediate byte appear as STOP. For example, [SWAPN, STOP] needs padding because the STOP is consumed as the immediate operand, not as an actual instruction. Add test to verify [SWAPN, STOP] is padded to [SWAPN, STOP, STOP].
Remove obsolete GasParams import and argument, use DummyHost::new() constructor instead of unit struct syntax.
Remove dupn_offset calculation from the main loop, keeping only PUSH handling. The SWAPN/DUPN/EXCHANGE padding logic via prev_opcode is retained for edge case handling.
These opcodes have 1-byte immediates that aren't handled by the main analysis loop, so we need extra padding to ensure safe execution regardless of whether the bytecode ends with STOP.
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This fixed the inconsistency in padding that immediates would do |
frangio
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Jan 20, 2026
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| let bytecode = vec![op]; | ||
| let (_, padded_bytecode) = analyze_legacy(bytecode.into()); | ||
| assert_eq!(padded_bytecode.len(), 2); | ||
| assert_eq!(padded_bytecode[0], op); | ||
| assert_eq!(padded_bytecode[1], opcode::STOP); |
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Is this right? This corresponds to a single instruction. My understanding was you always want a final STOP instruction. In that case, you'd expect 2 bytes of padding where the first is an immediate and the second is an instruction.
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Summary
analyze_legacypadding logic for SWAPN/DUPN/EXCHANGE edge cases usingprev_opcodetrackingTest plan