gh-149800: Generate the perf trampoline .eh_frame from the compiled assembly

Extract the .eh_frame the assembler emits for the trampoline object at
build time into trampoline_ehframe.h and patch only the FDE address
fields at runtime. Building with the perf trampoline now needs a host
Python, and configure disables the trampoline with a warning when none
is usable.

Author: stratakis

.gitignore

@@ -146,6 +146,7 @@ Tools/unicode/data/
 /dist/
 /jit_stencils*.h
 /jit_unwind_info*.h
+/trampoline_ehframe.h*
 .jit-stamp
 /platform
 /profile-clean-stamp

Doc/howto/perf_profiling.rst

@@ -30,7 +30,8 @@ relationship between this piece of code and the associated Python function using
     samply support on macOS is available starting from Python 3.15.
     Check the output of the ``configure`` build step or
     check the output of ``python -m sysconfig | grep HAVE_PERF_TRAMPOLINE``
-    to see if your system is supported.
+    to see if your system is supported. Building the perf trampoline needs a
+    Python interpreter, found by ``configure`` as ``PYTHON_FOR_REGEN``.
 
 For example, consider the following script:
 

Doc/using/configure.rst

@@ -25,6 +25,11 @@ To build CPython, you will need:
 
 * Support for threads.
 
+* Optionally, a Python interpreter, found by ``configure`` as
+  ``PYTHON_FOR_REGEN``, to build the perf trampoline (see
+  :doc:`/howto/perf_profiling`). Without it, ``configure`` disables the perf
+  trampoline.
+
 .. versionchanged:: 3.5
    On Windows, Visual Studio 2015 or later is now required.
 

Makefile.pre.in

@@ -3185,9 +3185,16 @@ jit_shim-universal2-apple-darwin.o: jit_shim-aarch64-apple-darwin.o jit_shim-x86
 Python/jit.o: $(srcdir)/Python/jit.c @JIT_STENCILS_H@
 	$(CC) -c $(PY_CORE_CFLAGS) -o $@ $<
 
-Python/jit_unwind.o: $(srcdir)/Python/jit_unwind.c $(JIT_UNWIND_INFO_H)
+TRAMPOLINE_EHFRAME_H = $(if @PERF_TRAMPOLINE_OBJ@,trampoline_ehframe.h)
+
+trampoline_ehframe.h: @PERF_TRAMPOLINE_OBJ@ $(srcdir)/Tools/jit/_trampoline_ehframe.py
+	$(PYTHON_FOR_REGEN) $(srcdir)/Tools/jit/_trampoline_ehframe.py \
+		-o $@ @PERF_TRAMPOLINE_OBJ@
+
+Python/jit_unwind.o: $(srcdir)/Python/jit_unwind.c $(JIT_UNWIND_INFO_H) $(TRAMPOLINE_EHFRAME_H)
 	$(CC) -c $(PY_CORE_CFLAGS) -o $@ $<
 
+
 .PHONY: regen-jit
 regen-jit: $(JIT_TARGETS)
 
@@ -3289,6 +3296,7 @@ clean-retain-profile: pycremoval
 	-rm -f Python/frozen_modules/MANIFEST
 	-find build -type f -a ! -name '*.gc??' -exec rm -f {} ';'
 	-rm -f Include/pydtrace_probes.h
+	-rm -f trampoline_ehframe.h trampoline_ehframe.h.tmp
 	-rm -f profile-gen-stamp
 	-rm -rf Platforms/Apple/iOS/testbed/Python.xcframework/ios-*/bin
 	-rm -rf Platforms/Apple/iOS/testbed/Python.xcframework/ios-*/lib

Misc/NEWS.d/next/Build/2026-09-09-14-23-23.gh-issue-149800.Ht8kaS.rst

@@ -0,0 +1,2 @@
+Generate the perf trampoline's unwind information from its compiled assembly
+at build time. Building the trampoline now requires a Python interpreter.