YJIT: Fix overlapping &mut in Assembler::code_gc()

Making overlapping `&mut`s triggers Undefined Bahavior. This function
previously had them through `cb` and `ocb` aliasing with `self` or live
references in the caller.

To fix the overlap, take `ocb` as a parameter and don't use `get_inline_cb()`
in the body of the function.

1 files changed, 6 insertions, 10 deletions

diff --git a/yjit/src/asm/mod.rs b/yjit/src/asm/mod.rs
index bf18dd5672..346ada7719 100644
--- a/yjit/src/asm/mod.rs
+++ b/yjit/src/asm/mod.rs
@@ -583,7 +583,7 @@ impl CodeBlock {
     }
 
     /// Code GC. Free code pages that are not on stack and reuse them.
-    pub fn code_gc(&mut self) {
+    pub fn code_gc(&mut self, ocb: &mut OutlinedCb) {
         // The previous code GC failed to free any pages. Give up.
         if self.freed_pages.as_ref() == &Some(vec![]) {
             return;
@@ -631,15 +631,11 @@ impl CodeBlock {
         freed_pages.append(&mut virtual_pages);
 
         if let Some(&first_page) = freed_pages.first() {
-            let mut cb = CodegenGlobals::get_inline_cb();
-            cb.write_pos = cb.get_page_pos(first_page);
-            cb.dropped_bytes = false;
-            cb.clear_comments();
-
-            let mut ocb = CodegenGlobals::get_outlined_cb().unwrap();
-            ocb.write_pos = ocb.get_page_pos(first_page);
-            ocb.dropped_bytes = false;
-            ocb.clear_comments();
+            for cb in [&mut *self, ocb.unwrap()] {
+                cb.write_pos = cb.get_page_pos(first_page);
+                cb.dropped_bytes = false;
+                cb.clear_comments();
+            }
         }
 
         // Track which pages are free.