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/// Disassemble NeoVM bytecode into a human-readable textual listing.
///
/// This function is total: any byte sequence (including malformed or
/// truncated bytecode) produces some output without panicking. That
/// invariant is fuzzed by `fuzz/fuzz_targets/fuzz_target_disasm.rs`.
pub fn disassemble_neovm_bytecode(bytecode: &[u8]) -> String {
let width = if bytecode.len() <= 0xFFFF { 4 } else { 6 };
let mut out = String::new();
let mut pc: usize = 0;
while pc < bytecode.len() {
let offset = pc;
let opcode = bytecode[pc];
pc += 1;
let opname = neo_devpack_solidity::runtime::spec::opcode_name(opcode)
.map(str::to_string)
.unwrap_or_else(|| format!("OP_{opcode:02X}"));
out.push_str(&format!("{offset:0width$X}: {opname}"));
match opcode {
// Push immediates
0x00 => {
// PUSHINT8
if let Some(v) = take_i8(bytecode, &mut pc) {
out.push_str(&format!(" {v}"));
} else {
out.push_str(" <unexpected EOF>");
break;
}
}
0x01 => {
// PUSHINT16
if let Some(v) = take_i16(bytecode, &mut pc) {
out.push_str(&format!(" {v}"));
} else {
out.push_str(" <unexpected EOF>");
break;
}
}
0x02 => {
// PUSHINT32
if let Some(v) = take_i32(bytecode, &mut pc) {
out.push_str(&format!(" {v}"));
} else {
out.push_str(" <unexpected EOF>");
break;
}
}
0x03 => {
// PUSHINT64
if let Some(v) = take_i64(bytecode, &mut pc) {
out.push_str(&format!(" {v}"));
} else {
out.push_str(" <unexpected EOF>");
break;
}
}
0x04 => {
// PUSHINT128 (raw LE bytes)
if let Some(bytes) = take(bytecode, &mut pc, 16) {
out.push_str(&format!(" 0x{}", hex::encode(bytes)));
} else {
out.push_str(" <unexpected EOF>");
break;
}
}
0x05 => {
// PUSHINT256 (raw LE bytes)
if let Some(bytes) = take(bytecode, &mut pc, 32) {
out.push_str(&format!(" 0x{}", hex::encode(bytes)));
} else {
out.push_str(" <unexpected EOF>");
break;
}
}
0x0A => {
// PUSHA — signed offset relative to this opcode (Pointer target).
if let Some(raw) = take_u32(bytecode, &mut pc) {
out.push_str(&format!(" {}", raw as i32));
} else {
out.push_str(" <unexpected EOF>");
break;
}
}
0x0C => {
// PUSHDATA1
let Some(len) = take_u8(bytecode, &mut pc) else {
out.push_str(" <unexpected EOF>");
break;
};
let Some(data) = take(bytecode, &mut pc, len as usize) else {
out.push_str(" <unexpected EOF>");
break;
};
out.push_str(&format!(" len={len} 0x{}", hex::encode(data)));
}
0x0D => {
// PUSHDATA2
let Some(len) = take_u16(bytecode, &mut pc) else {
out.push_str(" <unexpected EOF>");
break;
};
let Some(data) = take(bytecode, &mut pc, len as usize) else {
out.push_str(" <unexpected EOF>");
break;
};
out.push_str(&format!(" len={len} 0x{}", hex::encode(data)));
}
0x0E => {
// PUSHDATA4
let Some(len) = take_u32(bytecode, &mut pc) else {
out.push_str(" <unexpected EOF>");
break;
};
let Some(data) = take(bytecode, &mut pc, len as usize) else {
out.push_str(" <unexpected EOF>");
break;
};
out.push_str(&format!(" len={len} 0x{}", hex::encode(data)));
}
// Flow control (wide forms used by compiler)
0x23 // JMP_L
| 0x25 // JMPIF_L
| 0x27 // JMPIFNOT_L
| 0x29 // JMPEQ_L
| 0x2B // JMPNE_L
| 0x2D // JMPGT_L
| 0x2F // JMPGE_L
| 0x31 // JMPLT_L
| 0x33 // JMPLE_L
| 0x35 // CALL_L
| 0x3E // ENDTRY_L
=> {
let Some(rel) = take_i32(bytecode, &mut pc) else {
out.push_str(" <unexpected EOF>");
break;
};
out.push_str(&format!(" -> {}", fmt_target(bytecode.len(), offset, rel)));
}
0x3C => {
// TRY_L CatchOffset(int) FinallyOffset(int)
let Some(catch_rel) = take_i32(bytecode, &mut pc) else {
out.push_str(" <unexpected EOF>");
break;
};
let Some(finally_rel) = take_i32(bytecode, &mut pc) else {
out.push_str(" <unexpected EOF>");
break;
};
if catch_rel != 0 {
out.push_str(&format!(
" catch={}",
fmt_target(bytecode.len(), offset, catch_rel)
));
}
if finally_rel != 0 {
out.push_str(&format!(
" finally={}",
fmt_target(bytecode.len(), offset, finally_rel)
));
}
}
0x3B => {
// TRY CatchOffset(sbyte) FinallyOffset(sbyte)
let Some(catch_rel) = take_i8(bytecode, &mut pc) else {
out.push_str(" <unexpected EOF>");
break;
};
let Some(finally_rel) = take_i8(bytecode, &mut pc) else {
out.push_str(" <unexpected EOF>");
break;
};
if catch_rel != 0 {
out.push_str(&format!(
" catch={}",
fmt_target(bytecode.len(), offset, catch_rel as i32)
));
}
if finally_rel != 0 {
out.push_str(&format!(
" finally={}",
fmt_target(bytecode.len(), offset, finally_rel as i32)
));
}
}
0x22 // JMP
| 0x24 // JMPIF
| 0x26 // JMPIFNOT
| 0x28 // JMPEQ
| 0x2A // JMPNE
| 0x2C // JMPGT
| 0x2E // JMPGE
| 0x30 // JMPLT
| 0x32 // JMPLE
| 0x34 // CALL
| 0x3D // ENDTRY
=> {
let Some(rel) = take_i8(bytecode, &mut pc) else {
out.push_str(" <unexpected EOF>");
break;
};
out.push_str(&format!(
" -> {}",
fmt_target(bytecode.len(), offset, rel as i32)
));
}
// Slots / indices
0x56 => {
// INITSSLOT static_slots
let Some(count) = take_u8(bytecode, &mut pc) else {
out.push_str(" <unexpected EOF>");
break;
};
out.push_str(&format!(" {count}"));
}
0x57 => {
// INITSLOT locals,args
let Some(locals) = take_u8(bytecode, &mut pc) else {
out.push_str(" <unexpected EOF>");
break;
};
let Some(args) = take_u8(bytecode, &mut pc) else {
out.push_str(" <unexpected EOF>");
break;
};
out.push_str(&format!(" locals={locals} args={args}"));
}
0x5F | 0x67 | 0x6F | 0x77 | 0x7F | 0x87 => {
// LDSFLD/STSFLD/LDLOC/STLOC/LDARG/STARG (generic index form)
let Some(index) = take_u8(bytecode, &mut pc) else {
out.push_str(" <unexpected EOF>");
break;
};
out.push_str(&format!(" {index}"));
}
// Syscall
0x41 => {
let Some(id_bytes) = take(bytecode, &mut pc, 4) else {
out.push_str(" <unexpected EOF>");
break;
};
let id = [id_bytes[0], id_bytes[1], id_bytes[2], id_bytes[3]];
if let Some(name) = neo_devpack_solidity::runtime::spec::syscall_name(&id) {
out.push_str(&format!(" {name}"));
} else {
out.push_str(&format!(" 0x{}", hex::encode(id)));
}
}
// CALLT — calls a method token by 2-byte (u16 LE) token index. The
// operand MUST be consumed or every following instruction mis-aligns.
0x37 => {
let Some(idx_bytes) = take(bytecode, &mut pc, 2) else {
out.push_str(" <unexpected EOF>");
break;
};
let idx = u16::from_le_bytes([idx_bytes[0], idx_bytes[1]]);
out.push_str(&format!(" token={idx}"));
}
0xDB | 0xD9 => {
// CONVERT (0xDB) / ISTYPE (0xD9) take a mandatory 1-byte
// StackItemType operand. Without consuming it the operand byte
// was re-decoded as the next opcode, misaligning every
// subsequent instruction's offset in the listing (the compiler
// emits 0xDB 0x21 for essentially every storage-int load).
let Some(type_byte) = take(bytecode, &mut pc, 1) else {
out.push_str(" <unexpected EOF>");
break;
};
out.push_str(&format!(" type=0x{:02x}", type_byte[0]));
}
_ => {}
}
out.push('\n');
}
out
}