MASM Debug Output

To print VM state to standard output while a script runs, call the miden::core::debug procedures from your Miden Assembly. The client's transaction executor prints their output by default, so there is nothing to enable. Debugging is opt-in per script: output is produced only where a script calls a print procedure.

Procedures

Procedure	Prints
print_stack	the entire operand stack
print_mem	memory over a [start, end) range (consumes the two range arguments, at most 1024 addresses)
print_mem_addr	the memory cell at a single address
print_mem_all	every initialized memory cell of the current context

The operand-stack and memory printers are enabled by default. The advice-stack and advice-map printers are not, because they can expose witness data.

Example

Compile and execute a script that prints the operand stack:

let tx_script = client.code_builder().compile_tx_script(
    "
    use miden::core::debug
    use miden::core::sys

    @transaction_script
    pub proc main
        push.1.2.3
        exec.debug::print_stack
        drop drop drop
        exec.sys::truncate_stack
    end
    ",
)?;

client
    .execute_program(account_id, tx_script, AdviceInputs::default(), BTreeMap::new())
    .await?;

Executing it prints the operand stack to standard output (the step count includes the transaction prologue that runs before the script):

Stack state before step 2506:
├──  0: 3
├──  1: 2
├──  2: 1
└── (rest of the stack)

Under tests, pass --no-capture (cargo nextest, used by make test) or --nocapture (cargo test) to see the output.