test_c_stack_unwind fails on Linux LoongArch builds

Bug report

Bug description:

On the Linux LoongArch64 platform, the test_c_stack_unwind test fails because CPython's manually implemented frame-pointer unwinding mechanism fails to recognize the LoongArch stack frame layout (as it relies on the default FRAME_POINTER_NEXT_OFFSET and FRAME_POINTER_RETURN_OFFSET). This issue affects builds using both GCC and Clang.

In the LoongArch architecture, the frame pointer points to the caller's stack pointer; the previous frame pointer is stored at fp[-2], and the return address is stored at fp[-1].

Additionally, for CPython builds compiled with Clang, unexpected failures occur in test sections involving the GNU backtrace() function. By default, Clang/LoongArch generates .debug_frame sections but does not generate the .eh_frame unwinding tables required for runtime unwinding of CPython's C objects. Consequently, glibc's backtrace() returns only a single stack frame and cannot unwind through Python stack frames.

Reproducer

GCC build:

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

clang build:

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

Environment

• CPython main
• Linux LoongArch64
• GCC version: 15.3.0
• Clang 20.1.8
• glibc 2.42

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-152241
• gh-152578

Linux LoongArch64 上で GCC と Clang の両方を使って PYTHON_JIT=0 ./python -m test -v test_c_stack_unwind を実行し、その後、CPython に手動実装されているフレームポインタのアンワインド処理と、GNU backtrace() を使用しているテストセクションを調査します。テストが LoongArch のフレームレイアウトを認識し、該当する Clang のビルドテストが失敗しなくなれば完了です。リンクされた PR gh-152241 と gh-152578 は、作業がすでに進行中であることを示しています。