gh-152240: Fix test_c_stack_unwind on Linux LoongArch builds

[yzewei]

Fix test_c_stack_unwind on Linux LoongArch builds.

This change teaches _testinternalcapi's manual frame-pointer unwinder about
the LoongArch frame layout. On LoongArch, the frame pointer is the caller's
stack pointer; the previous frame pointer is at fp[-2], and the return
address is at fp[-1].

It also adds -funwind-tables for Linux LoongArch clang builds. clang/LoongArch
emits .debug_frame but not runtime .eh_frame unwind tables by default, so
glibc backtrace() cannot unwind through CPython frames unless unwind tables
are requested.

Validated on Linux LoongArch64:

GCC build:

../cpython/configure --with-pydebug CC=gcc
make -j8
PYTHON_JIT=0 ./python -m test -v test_c_stack_unwind

clang build with clang 20.1.8:

../cpython/configure --with-pydebug CC=clang
make -j8
PYTHON_JIT=0 ./python -m test -v test_c_stack_unwind

Also verified that -funwind-tables makes CPython C objects contain
.eh_frame, and the GNU backtrace test passes.

• Issue: test_c_stack_unwind fails on Linux LoongArch builds #152240

[python-cla-bot]

All commit authors signed the Contributor License Agreement.

[yzewei]

Fix log:

Gcc:

PYTHON_JIT=0 ./python -m test -v test_c_stack_unwind
== CPython 3.16.0a0 (heads/main-dirty:a00464bc33) [GCC 15.2.0 20250808]
== Linux-6.18.16-main-16k-loongarch64-with-glibc2.42 little-endian
== Python build: release
== cwd: /mnt/build-cpython-main-gcc-release/build/test_python_worker_480813æ
== CPU count: 8
== encodings: locale=UTF-8 FS=utf-8
== resources: all test resources are disabled, use -u option to unskip tests

Using random seed: 4035734376
0:00:00 load avg: 0.08 mem: 27.8 MiB Run 1 test sequentially in a single process
0:00:00 load avg: 0.08 mem: 27.8 MiB [1/1] test_c_stack_unwind
test_gnu_backtrace_jit_frames_disappear_after_executor_free (test.test_c_stack_unwind.GnuBacktraceUnwindTests.test_gnu_backtrace_jit_frames_disappear_after_executor_free) ... skipped 'JIT is not available'
test_gnu_backtrace_unwinds_through_jit_frames (test.test_c_stack_unwind.GnuBacktraceUnwindTests.test_gnu_backtrace_unwinds_through_jit_frames) ... #00 0x7fffe3601470 -> other
#01 0x555558360384 -> python
#02 0x5555585569fc -> python
#03 0x55555855e82c -> python
#04 0x55555856d86c -> python
#05 0x555558360384 -> python
#06 0x5555585570a4 -> python
#07 0x555558563cbc -> python
#08 0x55555856d86c -> python
#09 0x555558360384 -> python
#10 0x5555585570a4 -> python
#11 0x555558563cbc -> python
#12 0x55555856d86c -> python
#13 0x555558360384 -> python
#14 0x5555585570a4 -> python
#15 0x555558563cbc -> python
#16 0x55555856d86c -> python
#17 0x555558360384 -> python
#18 0x5555585570a4 -> python
#19 0x555558563cbc -> python
#20 0x55555856d86c -> python
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#23 0x555558563cbc -> python
#24 0x55555856d86c -> python
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#26 0x5555585570a4 -> python
#27 0x555558563cbc -> python
#28 0x55555856d86c -> python
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#30 0x5555585570a4 -> python
#31 0x555558563cbc -> python
#32 0x55555856d86c -> python
#33 0x555558360384 -> python
#34 0x5555585570a4 -> python
#35 0x555558563cbc -> python
#36 0x55555856d86c -> python
#37 0x555558360384 -> python
#38 0x5555585570a4 -> python
#39 0x555558563cbc -> python
#40 0x55555856d86c -> python
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#50 0x555558645a34 -> python
#51 0x7ffff22bd964 -> other
#52 0x7ffff22bda6c -> other
#53 0x5555582d694c -> python
{"length": 54, "python_frames": 51, "jit_frames": 0, "other_frames": 3, "jit_backend": null, "unwinder": "gnu_backtrace_unwind"}
ok
test_manual_unwind_finds_expected_frames (test.test_c_stack_unwind.ManualStackUnwindTests.test_manual_unwind_finds_expected_frames) ... #00 0x555558240384 -> python
#01 0x5555584369fc -> python
#02 0x55555843e82c -> python
#03 0x55555844d86c -> python
#04 0x555558240384 -> python
#05 0x5555584370a4 -> python
#06 0x555558443cbc -> python
#07 0x55555844d86c -> python
#08 0x555558240384 -> python
#09 0x5555584370a4 -> python
#10 0x555558443cbc -> python
#11 0x55555844d86c -> python
#12 0x555558240384 -> python
#13 0x5555584370a4 -> python
#14 0x555558443cbc -> python
#15 0x55555844d86c -> python
#16 0x555558240384 -> python
#17 0x5555584370a4 -> python
#18 0x555558443cbc -> python
#19 0x55555844d86c -> python
#20 0x555558240384 -> python
#21 0x5555584370a4 -> python
#22 0x555558443cbc -> python
#23 0x55555844d86c -> python
#24 0x555558240384 -> python
#25 0x5555584370a4 -> python
#26 0x555558443cbc -> python
#27 0x55555844d86c -> python
#28 0x555558240384 -> python
#29 0x5555584370a4 -> python
#30 0x555558443cbc -> python
#31 0x55555844d86c -> python
#32 0x555558240384 -> python
#33 0x5555584370a4 -> python
#34 0x555558443cbc -> python
#35 0x55555844d86c -> python
#36 0x555558240384 -> python
#37 0x5555584370a4 -> python
#38 0x555558443cbc -> python
#39 0x55555844d86c -> python
#40 0x555558240384 -> python
#41 0x555558240384 -> python
#42 0x5555584369fc -> python
#43 0x55555843e82c -> python
#44 0x55555844d510 -> python
#45 0x5555584e5d00 -> python
#46 0x5555584e622c -> python
#47 0x5555584e8efc -> python
#48 0x555558524a6c -> python
#49 0x555558525a34 -> python
#50 0x7ffff31dd964 -> other
#51 0x7ffff31dda6c -> other
#52 0x5555581b694c -> python
{"length": 53, "python_frames": 51, "jit_frames": 0, "other_frames": 2, "jit_backend": null, "unwinder": "manual_frame_pointer_unwind"}
ok

----------------------------------------------------------------------
Ran 3 tests in 1.347s

OK (skipped=1)
0:00:01 load avg: 0.08 mem: 28.3 MiB [1/1] test_c_stack_unwind passed

== Tests result: SUCCESS ==

1 test OK.

Total duration: 1.4 sec
Total tests: run=3 skipped=1
Total test files: run=1/1
Result: SUCCESS

Clang

PYTHON_JIT=0 ./python -m test -v test_c_stack_unwind
== CPython 3.16.0a0 (heads/main-dirty:a00464bc33) [Clang 20.1.8 ]
== Linux-6.18.16-main-16k-loongarch64-with-glibc2.42 little-endian
== Python build: debug
== cwd: /mnt/build-cpython-main-clang-debug/build/test_python_worker_480864æ
== CPU count: 8
== encodings: locale=UTF-8 FS=utf-8
== resources: all test resources are disabled, use -u option to unskip tests

Using random seed: 721941152
0:00:00 load avg: 0.02 mem: 31.4 MiB Run 1 test sequentially in a single process
0:00:00 load avg: 0.02 mem: 31.4 MiB [1/1] test_c_stack_unwind
test_gnu_backtrace_jit_frames_disappear_after_executor_free (test.test_c_stack_unwind.GnuBacktraceUnwindTests.test_gnu_backtrace_jit_frames_disappear_after_executor_free) ... skipped 'JIT is not available'
test_gnu_backtrace_unwinds_through_jit_frames (test.test_c_stack_unwind.GnuBacktraceUnwindTests.test_gnu_backtrace_unwinds_through_jit_frames) ... #00 0x7ffff008dea4 -> other
#01 0x555556ec1308 -> python
#02 0x555556e341e8 -> python
#03 0x555556ff546c -> python
#04 0x555556ffc0c8 -> python
#05 0x555556ff4adc -> python
#06 0x555556e341e8 -> python
#07 0x555556ff5a90 -> python
#08 0x555556ffdbd0 -> python
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#51 0x5555570e4a04 -> python
#52 0x55555711b6f8 -> python
#53 0x55555711bba8 -> python
#54 0x55555711bc0c -> python
#55 0x7ffff0f7d964 -> other
#56 0x7ffff0f7da6c -> other
#57 0x555556d8c9a4 -> python
{"length": 58, "python_frames": 55, "jit_frames": 0, "other_frames": 3, "jit_backend": null, "unwinder": "gnu_backtrace_unwind"}
ok
test_manual_unwind_finds_expected_frames (test.test_c_stack_unwind.ManualStackUnwindTests.test_manual_unwind_finds_expected_frames) ... #00 0x555556961308 -> python
#01 0x5555568d41e8 -> python
#02 0x555556a9546c -> python
#03 0x555556a9c0c8 -> python
#04 0x555556a94adc -> python
#05 0x5555568d41e8 -> python
#06 0x555556a95a90 -> python
#07 0x555556a9dbd0 -> python
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#09 0x5555568d41e8 -> python
#10 0x555556a95a90 -> python
#11 0x555556a9dbd0 -> python
#12 0x555556a94adc -> python
#13 0x5555568d41e8 -> python
#14 0x555556a95a90 -> python
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#40 0x555556a94adc -> python
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#44 0x555556a9546c -> python
#45 0x555556a9c0c8 -> python
#46 0x555556a94adc -> python
#47 0x555556a94714 -> python
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#50 0x555556b84a04 -> python
#51 0x555556bbb6f8 -> python
#52 0x555556bbbba8 -> python
#53 0x555556bbbc0c -> python
#54 0x7ffff028d964 -> other
#55 0x7ffff028da6c -> other
#56 0x55555682c9a4 -> python
{"length": 57, "python_frames": 55, "jit_frames": 0, "other_frames": 2, "jit_backend": null, "unwinder": "manual_frame_pointer_unwind"}
ok

----------------------------------------------------------------------
Ran 3 tests in 2.709s

OK (skipped=1)
0:00:02 load avg: 0.10 mem: 31.9 MiB [1/1] test_c_stack_unwind passed

== Tests result: SUCCESS ==

1 test OK.

Total duration: 2.8 sec
Total tests: run=3 skipped=1
Total test files: run=1/1
Result: SUCCESS