ZJIT: Add missing write barrier during profiling

Fixes `TestZJIT::test_require_rubygems`. It was crashing locally due to false collection of a live object. See <https://alanwu.space/post/write-barrier/>. Co-authored-by: Max Bernstein <max@bernsteinbear.com> Co-authored-by: Takashi Kokubun <takashi.kokubun@shopify.com> Co-authored-by: Stan Lo <stan.lo@shopify.com>
ruby · XrXr · Jul 16, 2025 · Jul 16, 2025 · Jul 16, 2025 · 077d4ac27044a6212d21947db3e7eef68f2b09eb
commit 077d4ac27044a6212d21947db3e7eef68f2b09eb
diff --git a/zjit/bindgen/src/main.rs b/zjit/bindgen/src/main.rs
@@ -167,6 +167,7 @@ fn main() {
         .allowlist_function("rb_gc_mark_movable")
         .allowlist_function("rb_gc_location")
         .allowlist_function("rb_gc_writebarrier")
+        .allowlist_function("rb_gc_writebarrier_remember")
 
         // VALUE variables for Ruby class objects
         // From include/ruby/internal/globals.h

diff --git a/zjit/src/cruby_bindings.inc.rs b/zjit/src/cruby_bindings.inc.rs
diff --git a/zjit/src/profile.rs b/zjit/src/profile.rs
@@ -89,6 +89,10 @@ fn profile_operands(profiler: &mut Profiler, profile: &mut IseqProfile, n: usize
         let opnd_type = Type::from_value(profiler.peek_at_stack((n - i - 1) as isize));
         types[i] = types[i].union(opnd_type);
     }
+    // In the loop above, we probably added a new reference to the profile through
+    // the VALUE in Type. It's messy and relatively slow to conditionally run a
+    // write barrier for each Type, so just remember to re-mark the iseq.
+    unsafe { rb_gc_writebarrier_remember(profiler.iseq.into()) };
 }
 
 #[derive(Debug)]