gh-151040: Fix `test_c_stack_unwind` on RISC-V (#152370)

diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index 6506bd53b0377ad2f098ff5734e54203854c9ee3..f6ff7820821ce128a5e2a1d5c8e554777c9371ed 100644 (file)
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -98,6 +98,11 @@ 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(__riscv)
+// RISC-V saves the return address at fp[-1], and the previous frame pointer at fp[-2].
+// See: https://riscv-non-isa.github.io/riscv-elf-psabi-doc/#_frame_pointer_convention
+#  define FRAME_POINTER_NEXT_OFFSET -2
+#  define FRAME_POINTER_RETURN_OFFSET -1
 #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