Exception Handling

Back to Runtime Specification

TRY / CATCH / FINALLY Opcodes

NeoVM supports structured exception handling:

• TRY begins a try block, specifying catch and/or finally offsets
• THROW raises an exception (top of stack becomes the exception object)
• ENDTRY exits the try block normally, jumping to the end offset
• ENDFINALLY exits the finally block; if an exception is pending, it is rethrown

Exception Propagation

1. When THROW is executed, the VM searches the current context's exception handler stack
2. If a catch handler is found, execution jumps to the catch offset with the exception on the stack
3. If a finally handler exists, it executes before propagation continues
4. If no handler is found in the current context, the exception propagates to the caller
5. ENDFINALLY rethrows any pending exception that was not handled by the catch block

Gas Effects

Gas continues to be consumed during exception handling. The TRY, ENDTRY, and ENDFINALLY opcodes each cost 1 gas unit. Stack unwinding during propagation does not have additional gas cost beyond the opcodes executed.