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fix: we do support empty bytes now #462

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fix: we do support empty bytes now #462

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0e3d2da
fix: we do support empty bytes now
daejunpark Mar 28, 2025
518857e
fix: apply preimage handling both PUSH and MLOAD
daejunpark Mar 28, 2025
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33 changes: 17 additions & 16 deletions src/halmos/sevm.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1785,6 +1785,18 @@ def assume_sha3_distinct(self, sha3_expr: BitVecRef) -> None:

self.sha3s[sha3_expr] = len(self.sha3s)

def try_preimage_sha3_hash(self, val):
if val.is_concrete:
if (inverse := sha3_inv.get(val.value)) is not None:
# restore precomputed hashes
return BV(self.sha3_data(con(inverse)), size=256)

# TODO: support more commonly used concrete keccak values
elif val.value == EMPTY_KECCAK:
return BV(self.sha3_data(b""), size=256)

return val

def new_gas_id(self) -> int:
self.cnts["gas"] += 1
return self.cnts["gas"]
Expand Down Expand Up @@ -3307,21 +3319,8 @@ def finalize(ex: Exec):
elif opcode == OP_PUSH32:
val = insn.operand
assert val.size == 256

# Special handling for PUSH32 with concrete values
if val.is_concrete:
if (inverse := sha3_inv.get(val.value)) is not None:
# restore precomputed hashes
state.push_any(ex.sha3_data(con(inverse)))

# TODO: support more commonly used concrete keccak values
elif val.value == EMPTY_KECCAK:
state.push_any(ex.sha3_data(b""))
else:
state.push(val)
else:
# Symbolic value
state.push(val)
val = ex.try_preimage_sha3_hash(val)
state.push(val)

elif opcode == OP_POP:
state.pop()
Expand Down Expand Up @@ -3408,7 +3407,9 @@ def finalize(ex: Exec):

elif opcode == OP_MLOAD:
loc: int = ex.mloc(check_size=True)
state.push_any(state.memory.get_word(loc))
val = BV(state.memory.get_word(loc), size=256)
val = ex.try_preimage_sha3_hash(val)
state.push(val)

elif opcode == OP_PUSH0:
state.push(ZERO)
Expand Down
5 changes: 2 additions & 3 deletions tests/regression/test/Sha3.t.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -37,9 +37,8 @@ contract Sha3Test is Test, SymTest {
function check_empty_hash_value() public {
assertEq(keccak256(""), EMPTY_HASH);

// TODO: uncomment when we support empty bytes
// bytes memory data = svm.createBytes(0, "data");
// assertEq(keccak256(data), EMPTY_HASH);
bytes memory data = svm.createBytes(0, "data");
assertEq(keccak256(data), EMPTY_HASH);
}

function check_only_empty_bytes_matches_empty_hash(bytes memory data) public {
Expand Down
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