The 3 warnings are as expected, please ignore:
"
#61: FILE: /root/test_shadow_stack.c:61:
+#define ARCH_SHSTK_WRSS (1ULL << 1)

WARNING: Prefer __always_inline over attribute((always_inline))
#84: FILE: /root/test_shadow_stack.c:84:
+static inline unsigned long attribute((always_inline)) get_ssp(void)

WARNING: Use of volatile is usually wrong: see Documentation/process/volatile-considered-harmful.rst
#206: FILE: /root/test_shadow_stack.c:206:
+volatile bool segv_triggered;

WARNING: Prefer noinline over attribute((noinline))
#209: FILE: /root/test_shadow_stack.c:209:
+void attribute((noinline)) violate_ss(void)
"
Thanks!

/* It's a test code not kernel code and it can't use always_inline. */
static inline unsigned long attribute((always_inline)) get_ssp(void)

/* The volatile is necessary for the tests. */
volatile bool segv_triggered;

/* It's a test code not kernel code and it can't use noinline. */
void attribute((noinline)) violate_ss(void)

Thanks Pengfei's explaination. The patch looks good to me.

Thanks Sun Yi's review!