YJIT: Reset dropped_bytes when patching code

We switch to a new page when we detect dropped_bytes flipping from false
to true. Previously, when we patch code for invalidation during code gc,
we start with the flag being set to true, so we failed to apply patches
that straddle pages. We would write out jumps half way and then stop,
which left the code corrupted.

Reset the flag before patching so we patch across pages properly.

1 files changed, 6 insertions, 0 deletions

diff --git a/yjit/src/asm/mod.rs b/yjit/src/asm/mod.rs
index 497f7687ed..4f3d20f5e5 100644
--- a/yjit/src/asm/mod.rs
+++ b/yjit/src/asm/mod.rs
@@ -463,6 +463,12 @@ impl CodeBlock {
         self.dropped_bytes
     }
 
+    /// To patch code that straddle pages correctly, we need to start with
+    /// the dropped bytes flag unset so we can detect when to switch to a new page.
+    pub fn set_dropped_bytes(&mut self, dropped_bytes: bool) {
+        self.dropped_bytes = dropped_bytes;
+    }
+
     /// Allocate a new label with a given name
     pub fn new_label(&mut self, name: String) -> usize {
         assert!(!name.contains(' '), "use underscores in label names, not spaces");