gh-152240: Fix test_c_stack_unwind on Linux LoongArch builds

Author: yzewei

Misc/NEWS.d/next/Build/2026-06-26-16-30-00.gh-issue-152240.loongarch.rst

@@ -0,0 +1,3 @@
+Fix C stack unwinding tests on Linux LoongArch builds. The manual frame
+pointer unwinder now recognizes the LoongArch frame layout, and clang builds
+now request runtime unwind tables.

Modules/_testinternalcapi.c

@@ -98,6 +98,12 @@ static const uintptr_t min_frame_pointer_addr = 0x1000;
 // https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi-1.9.html#STACK
 #  define FRAME_POINTER_NEXT_OFFSET 0
 #  define FRAME_POINTER_RETURN_OFFSET 2
+#elif defined(__loongarch__)
+// On LoongArch, the frame pointer is the caller's stack pointer.
+// The saved frame pointer is stored at fp[-2], and the return
+// address is stored at fp[-1].
+#  define FRAME_POINTER_NEXT_OFFSET -2
+#  define FRAME_POINTER_RETURN_OFFSET -1
 #else
 #  define FRAME_POINTER_NEXT_OFFSET 0
 #  define FRAME_POINTER_RETURN_OFFSET 1

configure

@@ -2631,6 +2631,16 @@ AS_VAR_IF([ac_cv_gcc_compat], [yes], [
 
     CFLAGS_NODIST="$CFLAGS_NODIST -std=c11"
 
+    AS_IF([test "$MACHDEP" = linux && test "$ac_cv_cc_name" = clang], [
+      AS_CASE([$host_cpu], [loongarch*], [
+        dnl clang/LoongArch emits only .debug_frame by default, which is not
+        dnl available to runtime unwinders such as backtrace().
+        AX_CHECK_COMPILE_FLAG([-funwind-tables], [
+          CFLAGS_NODIST="$CFLAGS_NODIST -funwind-tables"
+        ], [], [-Werror])
+      ])
+    ])
+
     PY_CHECK_CC_WARNING([enable], [extra], [if we can add -Wextra])
     AS_VAR_IF([ac_cv_enable_extra_warning], [yes],
               [CFLAGS_NODIST="$CFLAGS_NODIST -Wextra"])