solana-program-examples/basics/hello-solana/native/program/src/lib.rs

use solana_program::{
    account_info::AccountInfo, entrypoint, entrypoint::ProgramResult, msg, pubkey::Pubkey,
};

// Tells Solana that the entrypoint to this program
//  is the "process_instruction" function.
//
entrypoint!(process_instruction);

// Our entrypoint's parameters have to match the
//  anatomy of a transaction instruction (see README).
//
fn process_instruction(
    program_id: &Pubkey,
    _accounts: &[AccountInfo],
    _instruction_data: &[u8],
) -> ProgramResult {
    msg!("Hello, Solana!");

    msg!("Our program's Program ID: {}", &program_id);

    Ok(())
}