[debug] support guest program "println!"

[lispc]

Host(emulator) will handle the syscall, and print the content to stdout.

The circuits will treat this as a no-op.

[matthiasgoergens]

To add some context: we also need to specify what happens in the circuits.

I would also suggest making this a no-op in the circuits just for simplicity.

[naure]

There is a demo of this as a starting point:

ceno/examples/examples/ceno_rt_io.rs

Line 10 in 1edbf65

println!("📜📜📜 Hello, World!");

ceno/ceno_rt/src/io.rs

Line 72 in 1edbf65

macro_rules! println {

ceno/ceno_emul/tests/test_elf.rs

Line 70 in 1edbf65

assert_eq!(&all_messages[0], "📜📜📜 Hello, World!\n".as_bytes());

From there, to avoid the proving cost of even generating the message, we can use a a debug! macro (conditional prints or conditional compilation), and run the program in debug or production mode.