Just kidding, the flag breaks x86 linux

python · savannahostrowski · Apr 10, 2026 · Apr 10, 2026 · Apr 10, 2026 · Apr 10, 2026
commit 4e2a5d315310d4f7ad0467c4aa186eeab4392d4c
diff --git a/Misc/NEWS.d/next/Build/2026-04-10-20-57-30.gh-issue-146475.SWxwGM.rst b/Misc/NEWS.d/next/Build/2026-04-10-20-57-30.gh-issue-146475.SWxwGM.rst
@@ -1 +1 @@
-Use ``-fno-unwind-tables`` for JIT stencils to fix build failures with Apple LLVM 21.
+Strip CFI directives from JIT stencils to fix build failures with Apple LLVM 21.
@@ -251,7 +251,14 @@ 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 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 (e.g. Apple LLVM 21):
+        text = re.sub(r"^\s*\.cfi_\w+[^\n]*$", "", text, flags=re.MULTILINE)
+        return text
 
     def _parse_instruction(self, line: str) -> Instruction:
         target = None

diff --git a/Tools/jit/_targets.py b/Tools/jit/_targets.py
@@ -163,9 +163,10 @@ async def _compile(
             # __FILE__ macro and assert failure messages) for reproducibility:
             f"-ffile-prefix-map={CPYTHON}=.",
             f"-ffile-prefix-map={tempdir}=.",
-            # Don't emit CFI directives. The optimizer can produce unbalanced
-            # CFI directives that some assemblers reject (e.g. Apple LLVM 21):
-            "-fno-unwind-tables",
+            # 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 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:
Original file line number	Diff line number	Diff line change
		@@ -1 +1 @@
		Use ``-fno-unwind-tables`` for JIT stencils to fix build failures with Apple LLVM 21.
		Strip CFI directives from JIT stencils to fix build failures with Apple LLVM 21.