Strip CFI directives in JIT stencils

Author: savannahostrowski

Tools/jit/_optimizers.py

@@ -251,7 +251,15 @@ def _preprocess(self, text: str) -> str:
         # references to a local _JIT_CONTINUE label (which we will add later):
         continue_symbol = rf"\b{re.escape(self.symbol_prefix)}_JIT_CONTINUE\b"
         continue_label = f"{self.label_prefix}_JIT_CONTINUE"
-        return re.sub(continue_symbol, continue_label, text)
+        text = re.sub(continue_symbol, continue_label, text)
+        # Strip CFI directives. JIT stencils are compiled with
+        # -fno-asynchronous-unwind-tables and don't use DWARF CFI unwind
+        # tables (.eh_frame).
+        # The optimizer's dead code elimination can remove blocks containing
+        # .cfi_endproc while keeping the corresponding .cfi_startproc,
+        # producing unbalanced CFI frames that some assemblers reject:
+        text = re.sub(r"^\s*\.cfi_\w+[^\n]*$", "", text, flags=re.MULTILINE)
+        return text
 
     def _parse_instruction(self, line: str) -> Instruction:
         target = None