ZJIT: Have JITFrame relocate itself via Rust function

Expose rb_zjit_jit_frame_update_references so vm.c can call into Rust
to relocate the iseq pointer during GC compaction, instead of manually
manipulating JITFrame fields in C. This keeps JITFrame field access
consolidated in Rust.

Author: k0kubun

vm.c

@@ -3672,11 +3672,7 @@ rb_execution_context_update(rb_execution_context_t *ec)
             const VALUE *ep = cfp->ep;
             cfp->self = rb_gc_location(cfp->self);
             if (rb_zjit_enabled_p && CFP_HAS_JIT_RETURN(cfp)) {
-                zjit_jit_frame_t *jit_frame = (zjit_jit_frame_t *)cfp->jit_return;
-                if (jit_frame->iseq) {
-                    // ISEQ frame with JITFrame: relocate iseq in JITFrame
-                    jit_frame->iseq = (const rb_iseq_t *)rb_gc_location((VALUE)jit_frame->iseq);
-                }
+                rb_zjit_jit_frame_update_references((zjit_jit_frame_t *)cfp->jit_return);
                 // block_code must always be relocated. For ISEQ frames, the JIT caller
                 // may have written it (gen_block_handler_specval) for passing blocks.
                 // For C frames, rb_iterate0 may have written an ifunc to block_code

zjit.h

@@ -45,6 +45,7 @@ void rb_zjit_before_ractor_spawn(void);
 void rb_zjit_tracing_invalidate_all(void);
 void rb_zjit_invalidate_no_singleton_class(VALUE klass);
 void rb_zjit_invalidate_root_box(void);
+void rb_zjit_jit_frame_update_references(zjit_jit_frame_t *jit_frame);
 #else
 #define rb_zjit_entry 0
 static inline void rb_zjit_compile_iseq(const rb_iseq_t *iseq, rb_execution_context_t *ec, bool jit_exception) {}
@@ -58,6 +59,7 @@ static inline void rb_zjit_before_ractor_spawn(void) {}
 static inline void rb_zjit_tracing_invalidate_all(void) {}
 static inline void rb_zjit_invalidate_no_singleton_class(VALUE klass) {}
 static inline void rb_zjit_invalidate_root_box(void) {}
+static inline void rb_zjit_jit_frame_update_references(zjit_jit_frame_t *jit_frame) {}
 #endif // #if USE_ZJIT
 
 #define rb_zjit_enabled_p (rb_zjit_entry != 0)

zjit/src/jit_frame.rs

@@ -43,6 +43,13 @@ impl JITFrame {
     }
 }
 
+/// Update the iseq pointer in an on-stack JITFrame during GC compaction.
+/// Called from rb_execution_context_update in vm.c.
+#[unsafe(no_mangle)]
+pub extern "C" fn rb_zjit_jit_frame_update_references(jit_frame: *mut JITFrame) {
+    unsafe { &mut *jit_frame }.update_references();
+}
+
 #[cfg(test)]
 mod tests {
     use crate::cruby::{eval, inspect};