oooo there is a flag

Author: savannahostrowski

Misc/NEWS.d/next/Build/2026-04-10-20-57-30.gh-issue-146475.SWxwGM.rst

@@ -1 +1 @@
-Strip CFI directives from JIT stencils to fix build failures with Apple LLVM 21.
+Use ``-fno-unwind-tables`` for JIT stencils to fix build failures with Apple LLVM 21.

Tools/jit/_optimizers.py

@@ -251,14 +251,7 @@ 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"
-        text = re.sub(continue_symbol, continue_label, text)
-        # Strip CFI directives as JIT stencils are compiled with
-        # -fno-asynchronous-unwind-tables. The optimizer 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
+        return re.sub(continue_symbol, continue_label, text)
 
     def _parse_instruction(self, line: str) -> Instruction:
         target = None

Tools/jit/_targets.py

@@ -163,10 +163,11 @@ async def _compile(
             # __FILE__ macro and assert failure messages) for reproducibility:
             f"-ffile-prefix-map={CPYTHON}=.",
             f"-ffile-prefix-map={tempdir}=.",
-            # This debug info isn't necessary, and bloats out the JIT'ed code.
-            # We *may* be able to re-enable this, process it, and JIT it for a
-            # nicer debugging experience... but that needs a lot more research:
-            "-fno-asynchronous-unwind-tables",
+            # Don't emit unwind tables or CFI directives. JIT stencils are
+            # not standard functions and their unwind info is not usable at
+            # runtime. The optimizer can produce unbalanced CFI directives
+            # that some assemblers reject (e.g. Apple LLVM 21):
+            "-fno-unwind-tables",
             # Don't call built-in functions that we can't find or patch:
             "-fno-builtin",
             # Don't call stack-smashing canaries that we can't find or patch: