arm64: ftrace: enable graph FP test

The core frace code has an optional sanity check on the frame pointer
passed by ftrace_graph_caller and return_to_handler. This is cheap,
useful, and enabled unconditionally on x86, sparc, and riscv.

Let's do the same on arm64, so that we can catch any problems early.
Signed-off-by: NMark Rutland <mark.rutland@arm.com>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Torsten Duwe <duwe@suse.de>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>

arch/arm64/include/asm/ftrace.h

@@ -13,6 +13,7 @@
 
 #include <asm/insn.h>
 
+#define HAVE_FUNCTION_GRAPH_FP_TEST
 #define MCOUNT_ADDR		((unsigned long)_mcount)
 #define MCOUNT_INSN_SIZE	AARCH64_INSN_SIZE
 

arch/arm64/kernel/entry-ftrace.S

@@ -207,8 +207,7 @@ ENDPROC(ftrace_graph_caller)
  * void return_to_handler(void)
  *
  * Run ftrace_return_to_handler() before going back to parent.
- * @fp is checked against the value passed by ftrace_graph_caller()
- * only when HAVE_FUNCTION_GRAPH_FP_TEST is enabled.
+ * @fp is checked against the value passed by ftrace_graph_caller().
  */
 ENTRY(return_to_handler)
 	save_return_regs