wasm interpreter: use lookup table instead of unsafe

crates/wasm_module/src/opcodes.rs

@@ -2,6 +2,7 @@ use crate::Serialize;
 
 use super::parse::{Parse, ParseError, SkipBytes};
 
+// NOTE: when adding a new variant, be sure to add it to LOOKUP_TABLE below as well
 #[repr(u8)]
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum OpCode {
@@ -186,9 +187,197 @@ pub enum OpCode {
     F64REINTERPRETI64 = 0xbf,
 }
 
+pub const LOOKUP_TABLE: [Option<OpCode>; 256] = {
+    use OpCode::*;
+
+    let mut result = [None; 256];
+
+    result[0x00] = Some(UNREACHABLE);
+    result[0x01] = Some(NOP);
+    result[0x02] = Some(BLOCK);
+    result[0x03] = Some(LOOP);
+    result[0x04] = Some(IF);
+    result[0x05] = Some(ELSE);
+    result[0x0b] = Some(END);
+    result[0x0c] = Some(BR);
+    result[0x0d] = Some(BRIF);
+    result[0x0e] = Some(BRTABLE);
+    result[0x0f] = Some(RETURN);
+    result[0x10] = Some(CALL);
+    result[0x11] = Some(CALLINDIRECT);
+    result[0x1a] = Some(DROP);
+    result[0x1b] = Some(SELECT);
+    result[0x20] = Some(GETLOCAL);
+    result[0x21] = Some(SETLOCAL);
+    result[0x22] = Some(TEELOCAL);
+    result[0x23] = Some(GETGLOBAL);
+    result[0x24] = Some(SETGLOBAL);
+    result[0x28] = Some(I32LOAD);
+    result[0x29] = Some(I64LOAD);
+    result[0x2a] = Some(F32LOAD);
+    result[0x2b] = Some(F64LOAD);
+    result[0x2c] = Some(I32LOAD8S);
+    result[0x2d] = Some(I32LOAD8U);
+    result[0x2e] = Some(I32LOAD16S);
+    result[0x2f] = Some(I32LOAD16U);
+    result[0x30] = Some(I64LOAD8S);
+    result[0x31] = Some(I64LOAD8U);
+    result[0x32] = Some(I64LOAD16S);
+    result[0x33] = Some(I64LOAD16U);
+    result[0x34] = Some(I64LOAD32S);
+    result[0x35] = Some(I64LOAD32U);
+    result[0x36] = Some(I32STORE);
+    result[0x37] = Some(I64STORE);
+    result[0x38] = Some(F32STORE);
+    result[0x39] = Some(F64STORE);
+    result[0x3a] = Some(I32STORE8);
+    result[0x3b] = Some(I32STORE16);
+    result[0x3c] = Some(I64STORE8);
+    result[0x3d] = Some(I64STORE16);
+    result[0x3e] = Some(I64STORE32);
+    result[0x3f] = Some(CURRENTMEMORY);
+    result[0x40] = Some(GROWMEMORY);
+    result[0xfc] = Some(MEMORY);
+    result[0x41] = Some(I32CONST);
+    result[0x42] = Some(I64CONST);
+    result[0x43] = Some(F32CONST);
+    result[0x44] = Some(F64CONST);
+    result[0x45] = Some(I32EQZ);
+    result[0x46] = Some(I32EQ);
+    result[0x47] = Some(I32NE);
+    result[0x48] = Some(I32LTS);
+    result[0x49] = Some(I32LTU);
+    result[0x4a] = Some(I32GTS);
+    result[0x4b] = Some(I32GTU);
+    result[0x4c] = Some(I32LES);
+    result[0x4d] = Some(I32LEU);
+    result[0x4e] = Some(I32GES);
+    result[0x4f] = Some(I32GEU);
+    result[0x50] = Some(I64EQZ);
+    result[0x51] = Some(I64EQ);
+    result[0x52] = Some(I64NE);
+    result[0x53] = Some(I64LTS);
+    result[0x54] = Some(I64LTU);
+    result[0x55] = Some(I64GTS);
+    result[0x56] = Some(I64GTU);
+    result[0x57] = Some(I64LES);
+    result[0x58] = Some(I64LEU);
+    result[0x59] = Some(I64GES);
+    result[0x5a] = Some(I64GEU);
+    result[0x5b] = Some(F32EQ);
+    result[0x5c] = Some(F32NE);
+    result[0x5d] = Some(F32LT);
+    result[0x5e] = Some(F32GT);
+    result[0x5f] = Some(F32LE);
+    result[0x60] = Some(F32GE);
+    result[0x61] = Some(F64EQ);
+    result[0x62] = Some(F64NE);
+    result[0x63] = Some(F64LT);
+    result[0x64] = Some(F64GT);
+    result[0x65] = Some(F64LE);
+    result[0x66] = Some(F64GE);
+    result[0x67] = Some(I32CLZ);
+    result[0x68] = Some(I32CTZ);
+    result[0x69] = Some(I32POPCNT);
+    result[0x6a] = Some(I32ADD);
+    result[0x6b] = Some(I32SUB);
+    result[0x6c] = Some(I32MUL);
+    result[0x6d] = Some(I32DIVS);
+    result[0x6e] = Some(I32DIVU);
+    result[0x6f] = Some(I32REMS);
+    result[0x70] = Some(I32REMU);
+    result[0x71] = Some(I32AND);
+    result[0x72] = Some(I32OR);
+    result[0x73] = Some(I32XOR);
+    result[0x74] = Some(I32SHL);
+    result[0x75] = Some(I32SHRS);
+    result[0x76] = Some(I32SHRU);
+    result[0x77] = Some(I32ROTL);
+    result[0x78] = Some(I32ROTR);
+    result[0x79] = Some(I64CLZ);
+    result[0x7a] = Some(I64CTZ);
+    result[0x7b] = Some(I64POPCNT);
+    result[0x7c] = Some(I64ADD);
+    result[0x7d] = Some(I64SUB);
+    result[0x7e] = Some(I64MUL);
+    result[0x7f] = Some(I64DIVS);
+    result[0x80] = Some(I64DIVU);
+    result[0x81] = Some(I64REMS);
+    result[0x82] = Some(I64REMU);
+    result[0x83] = Some(I64AND);
+    result[0x84] = Some(I64OR);
+    result[0x85] = Some(I64XOR);
+    result[0x86] = Some(I64SHL);
+    result[0x87] = Some(I64SHRS);
+    result[0x88] = Some(I64SHRU);
+    result[0x89] = Some(I64ROTL);
+    result[0x8a] = Some(I64ROTR);
+    result[0x8b] = Some(F32ABS);
+    result[0x8c] = Some(F32NEG);
+    result[0x8d] = Some(F32CEIL);
+    result[0x8e] = Some(F32FLOOR);
+    result[0x8f] = Some(F32TRUNC);
+    result[0x90] = Some(F32NEAREST);
+    result[0x91] = Some(F32SQRT);
+    result[0x92] = Some(F32ADD);
+    result[0x93] = Some(F32SUB);
+    result[0x94] = Some(F32MUL);
+    result[0x95] = Some(F32DIV);
+    result[0x96] = Some(F32MIN);
+    result[0x97] = Some(F32MAX);
+    result[0x98] = Some(F32COPYSIGN);
+    result[0x99] = Some(F64ABS);
+    result[0x9a] = Some(F64NEG);
+    result[0x9b] = Some(F64CEIL);
+    result[0x9c] = Some(F64FLOOR);
+    result[0x9d] = Some(F64TRUNC);
+    result[0x9e] = Some(F64NEAREST);
+    result[0x9f] = Some(F64SQRT);
+    result[0xa0] = Some(F64ADD);
+    result[0xa1] = Some(F64SUB);
+    result[0xa2] = Some(F64MUL);
+    result[0xa3] = Some(F64DIV);
+    result[0xa4] = Some(F64MIN);
+    result[0xa5] = Some(F64MAX);
+    result[0xa6] = Some(F64COPYSIGN);
+    result[0xa7] = Some(I32WRAPI64);
+    result[0xa8] = Some(I32TRUNCSF32);
+    result[0xa9] = Some(I32TRUNCUF32);
+    result[0xaa] = Some(I32TRUNCSF64);
+    result[0xab] = Some(I32TRUNCUF64);
+    result[0xac] = Some(I64EXTENDSI32);
+    result[0xad] = Some(I64EXTENDUI32);
+    result[0xae] = Some(I64TRUNCSF32);
+    result[0xaf] = Some(I64TRUNCUF32);
+    result[0xb0] = Some(I64TRUNCSF64);
+    result[0xb1] = Some(I64TRUNCUF64);
+    result[0xb2] = Some(F32CONVERTSI32);
+    result[0xb3] = Some(F32CONVERTUI32);
+    result[0xb4] = Some(F32CONVERTSI64);
+    result[0xb5] = Some(F32CONVERTUI64);
+    result[0xb6] = Some(F32DEMOTEF64);
+    result[0xb7] = Some(F64CONVERTSI32);
+    result[0xb8] = Some(F64CONVERTUI32);
+    result[0xb9] = Some(F64CONVERTSI64);
+    result[0xba] = Some(F64CONVERTUI64);
+    result[0xbb] = Some(F64PROMOTEF32);
+    result[0xbc] = Some(I32REINTERPRETF32);
+    result[0xbd] = Some(I64REINTERPRETF64);
+    result[0xbe] = Some(F32REINTERPRETI32);
+    result[0xbf] = Some(F64REINTERPRETI64);
+
+    result
+};
+
 impl From<u8> for OpCode {
-    fn from(x: u8) -> Self {
-        unsafe { std::mem::transmute(x) }
+    fn from(value: u8) -> Self {
+        // invalid instruction bytes can be genuine because we don't support all instructions, and
+        // new ones get added or stabilized. It could also be a bug in the interpreter, e.g. some
+        // opcode does not move the instruction pointer correctly.
+        match LOOKUP_TABLE[value as usize] {
+            None => unreachable!("unsupported instruction byte {value:#x?}"),
+            Some(op) => op,
+        }
     }
 }