Some cleanups.

src/backend/runtime.rs

@@ -1,7 +1,9 @@
 use cranelift_codegen::ir::{types, AbiParam, FuncRef, Function, Signature};
 use cranelift_codegen::isa::CallConv;
+use cranelift_jit::JITBuilder;
 use cranelift_module::{FuncId, Linkage, Module, ModuleResult};
 use std::collections::HashMap;
+use std::ffi::CStr;
 use target_lexicon::Triple;
 use thiserror::Error;
 
@@ -16,6 +18,12 @@ pub enum RuntimeFunctionError {
     CannotFindRuntimeFunction(String),
 }
 
+extern "C" fn runtime_print(name: *const i8, value: u64) {
+    let cstr = unsafe { CStr::from_ptr(name) };
+    let reconstituted = cstr.to_string_lossy();
+    println!("{} = {}", reconstituted, value);
+}
+
 impl RuntimeFunctions {
     pub fn new<M: Module>(platform: &Triple, module: &mut M) -> ModuleResult<RuntimeFunctions> {
         let mut builtin_functions = HashMap::new();
@@ -54,4 +62,9 @@ impl RuntimeFunctions {
             Some(func_id) => Ok(module.declare_func_in_func(*func_id, func)),
         }
     }
+
+    pub fn register_jit_implementations(builder: &mut JITBuilder) {
+        builder.symbol("print", runtime_print as *const u8);
+    }
+
 }