arm64: add SIGSYS siginfo for compat task

SIGSYS is primarily used in secure computing to notify tracer of syscall
events. This patch allows signal handler on compat task to get correct
information with SA_SIGINFO specified when this signal is delivered.

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/compat.h

@@ -205,6 +205,13 @@ typedef struct compat_siginfo {
 			compat_long_t _band;	/* POLL_IN, POLL_OUT, POLL_MSG */
 			int _fd;
 		} _sigpoll;
+
+		/* SIGSYS */
+		struct {
+			compat_uptr_t _call_addr; /* calling user insn */
+			int _syscall;	/* triggering system call number */
+			compat_uint_t _arch;	/* AUDIT_ARCH_* of syscall */
+		} _sigsys;
 	} _sifields;
 } compat_siginfo_t;