William PR comments

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

@@ -155,8 +155,8 @@ min_stack_len_for_opcode:
     BYTES 2  // 0x05, SDIV
     BYTES 2  // 0x06, MOD
     BYTES 2  // 0x07, SMOD
-    BYTES 2  // 0x08, ADDMOD
+    BYTES 3  // 0x08, ADDMOD
-    BYTES 2  // 0x09, MULMOD
+    BYTES 3  // 0x09, MULMOD
     BYTES 2  // 0x0a, EXP
     BYTES 2  // 0x0b, SIGNEXTEND
     %rep 4  // 0x0c-0x0f, invalid
@@ -222,7 +222,7 @@ min_stack_len_for_opcode:
     BYTES 1  // 0x54, SLOAD
     BYTES 2  // 0x55, SSTORE
     BYTES 1  // 0x56, JUMP
-    BYTES 1  // 0x57, JUMPI
+    BYTES 2  // 0x57, JUMPI
     BYTES 0  // 0x58, PC
     BYTES 0  // 0x59, MSIZE
     BYTES 0  // 0x5a, GAS

evm/src/witness/errors.rs

@@ -11,6 +11,7 @@ pub enum ProgramError {
     StackOverflow,
     KernelPanic,
     MemoryError(MemoryError),
+    GasLimitError,
 }
 
 #[allow(clippy::enum_variant_names)]

evm/src/witness/operation.rs

@@ -502,7 +502,7 @@ pub(crate) fn generate_syscall<F: Field>(
     mut row: CpuColumnsView<F>,
 ) -> Result<(), ProgramError> {
     if TryInto::<u32>::try_into(state.registers.gas_used).is_err() {
-        panic!();
+        return Err(ProgramError::GasLimitError);
     }
 
     if state.registers.stack_len < stack_values_read {
@@ -544,13 +544,18 @@ pub(crate) fn generate_syscall<F: Field>(
     let syscall_info = U256::from(state.registers.program_counter + 1)
         + (U256::from(u64::from(state.registers.is_kernel)) << 32)
         + (U256::from(state.registers.gas_used) << 192);
-    let log_out = stack_push_log_and_fill(state, &mut row, syscall_info)?;
 
+    // Set registers before pushing to the stack; in particular, we need to set kernel mode so we
+    // can't incorrectly trigger a stack overflow. However, note that we have to do it _after_ we
+    // make `syscall_info`, which should contain the old values.
     state.registers.program_counter = new_program_counter;
-    log::debug!("Syscall to {}", KERNEL.offset_name(new_program_counter));
     state.registers.is_kernel = true;
     state.registers.gas_used = 0;
 
+    let log_out = stack_push_log_and_fill(state, &mut row, syscall_info)?;
+
+    log::debug!("Syscall to {}", KERNEL.offset_name(new_program_counter));
+
     state.traces.push_memory(log_in0);
     state.traces.push_memory(log_in1);
     state.traces.push_memory(log_in2);
@@ -680,7 +685,7 @@ pub(crate) fn generate_exception<F: Field>(
     mut row: CpuColumnsView<F>,
 ) -> Result<(), ProgramError> {
     if TryInto::<u32>::try_into(state.registers.gas_used).is_err() {
-        panic!();
+        return Err(ProgramError::GasLimitError);
     }
 
     row.stack_len_bounds_aux = (row.stack_len + F::ONE).inverse();
@@ -719,13 +724,18 @@ pub(crate) fn generate_exception<F: Field>(
 
     let exc_info =
         U256::from(state.registers.program_counter) + (U256::from(state.registers.gas_used) << 192);
-    let log_out = stack_push_log_and_fill(state, &mut row, exc_info)?;
 
+    // Set registers before pushing to the stack; in particular, we need to set kernel mode so we
+    // can't incorrectly trigger a stack overflow. However, note that we have to do it _after_ we
+    // make `exc_info`, which should contain the old values.
     state.registers.program_counter = new_program_counter;
-    log::debug!("Exception to {}", KERNEL.offset_name(new_program_counter));
     state.registers.is_kernel = true;
     state.registers.gas_used = 0;
 
+    let log_out = stack_push_log_and_fill(state, &mut row, exc_info)?;
+
+    log::debug!("Exception to {}", KERNEL.offset_name(new_program_counter));
+
     state.traces.push_memory(log_in0);
     state.traces.push_memory(log_in1);
     state.traces.push_memory(log_in2);