Add length method ffi/jitfn abstract values.

CHANGELOG.md

@@ -2,10 +2,12 @@
 All notable changes to this project will be documented in this file.
 
 ## ??? - Unreleased
+- Add `ffi/jitfn` to allow calling function pointers generated at runtime from machine code.
+  Bring your own assembler, though.
 - Channels can now be marshalled. Pending state is not saved, only items in the channel.
 - Use the new `.length` function pointer on abstract types for lengths. Adding
   a `length` method will still work as well.
-- Support byte views on abstract types with the `bytes` function pointer.
+- Support byte views on abstract types with the `.bytes` function pointer.
 - Add the `u` format specifier to printf family functions.
 - Allow printing 64 integer types in `printf` and `string/format` family functions.
 - Allow importing modules from custom directories more easily with the `@` prefix

examples/jitfn/jitfn.janet

@@ -10,3 +10,4 @@
 (def signature (ffi/signature :default :void))
 (ffi/call f signature)
 (print "called a jitted function with FFI!")
+(print "machine code: " (describe (string/slice f)))

src/core/ffi.c

@@ -244,10 +244,17 @@ static JanetByteView janet_ffijit_getbytes(void *p, size_t s) {
     return bytes;
 }
 
+static size_t janet_ffijit_length(void *p, size_t s) {
+    (void) s;
+    JanetFFIJittedFn *fn = p;
+    return fn->size;
+}
+
 const JanetAbstractType janet_type_ffijit = {
     .name = "ffi/jitfn",
     .gc = janet_ffijit_gc,
-    .bytes = janet_ffijit_getbytes
+    .bytes = janet_ffijit_getbytes,
+    .length = janet_ffijit_length
 };
 
 typedef struct {