Minor bugfixes

evm/src/cpu/kernel/asm/core/exception.asm

@@ -96,11 +96,20 @@ global exc_invalid_jumpi_destination:
 
 
 global invalid_jump_jumpi_destination_common:
+    // We have a jump destination on the stack. We want to `PANIC` if it is valid, and jump to
+    // `fault_exception` if it is not. An address is a valid jump destination if it points to a
+    // `JUMPDEST` instruction. In practice, since in this implementation memory addresses are
+    // limited to 32 bits, we check two things:
+    //  1. the address is no more than 32 bits long, and
+    //  2. it points to a `JUMPDEST` instruction.
     // stack: jump_dest
+    DUP1
+    %shr_const(32)
+    %jumpi(fault_exception) // This keeps one copy of jump_dest on the stack, but that's fine.
+    // jump_dest is a valid address; check if it points to a `JUMP_DEST`.
     %mload_current(@SEGMENT_JUMPDEST_BITS)
     // stack: is_valid_jumpdest
-    // if valid, then the trap should never have been entered
-    %jumpi(panic)
+    %jumpi(panic) // Trap should never have been entered.
     %jump(fault_exception)
 
 
@@ -164,7 +173,7 @@ min_stack_len_for_opcode:
     BYTES 2  // 0x17, OR
     BYTES 2  // 0x18, XOR
     BYTES 1  // 0x19, NOT
-    BYTES 2  // 0x1a, BYTES
+    BYTES 2  // 0x1a, BYTE
     BYTES 2  // 0x1b, SHL
     BYTES 2  // 0x1c, SHR
     BYTES 2  // 0x1d, SAR

evm/src/witness/gas.rs

@@ -14,7 +14,6 @@ pub(crate) fn gas_to_charge(op: Operation) -> u64 {
     match op {
         Iszero => G_VERYLOW,
         Not => G_VERYLOW,
-        Byte => G_VERYLOW,
         Syscall(_, _, _) => KERNEL_ONLY_INSTR,
         Eq => G_VERYLOW,
         BinaryLogic(_) => G_VERYLOW,

evm/src/witness/transition.rs

@@ -157,7 +157,6 @@ fn fill_op_flag<F: Field>(op: Operation, row: &mut CpuColumnsView<F>) {
         Operation::Swap(_) => &mut flags.swap,
         Operation::Iszero => &mut flags.iszero,
         Operation::Not => &mut flags.not,
-        Operation::Byte => &mut flags.byte,
         Operation::Syscall(_, _, _) => &mut flags.syscall,
         Operation::Eq => &mut flags.eq,
         Operation::BinaryLogic(logic::Op::And) => &mut flags.and,