Helper for si_code event extraction.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/ptrace.h

@@ -32,6 +32,8 @@
 #define PTRACE_O_TRACEVFORKDONE	0x00000020
 #define PTRACE_O_TRACEEXIT	0x00000040
 
+#define SI_EVENT(_si_code)	(((_si_code) & 0xFFFF) >> 8)
+
 extern int seize_task(pid_t pid, pid_t ppid, pid_t *pgid, pid_t *sid);
 extern int unseize_task(pid_t pid, int state);
 extern int ptrace_peek_area(pid_t pid, void *dst, void *addr, long bytes);

parasite-syscall.c

@@ -171,7 +171,7 @@ retry_signal:
 			goto err;
 		}
 
-		if (((siginfo.si_code & 0xffff) >> 8) != PTRACE_EVENT_STOP)
+		if (SI_EVENT(siginfo.si_code) != PTRACE_EVENT_STOP)
 			goto retry_signal;
 
 		/*
@@ -218,7 +218,7 @@ retry_signal:
 		goto err;
 	}
 
-	if (((siginfo.si_code & 0xffff) >> 8) != PTRACE_EVENT_STOP) {
+	if (SI_EVENT(siginfo.si_code) != PTRACE_EVENT_STOP) {
 		pr_err("si_code doesn't match (pid: %d si_code: %d)\n",
 			pid, siginfo.si_code);
 		goto err;

ptrace.c

@@ -113,7 +113,7 @@ try_again:
 		goto err;
 	}
 
-	if (((si.si_code & 0xffff)>> 8) != PTRACE_EVENT_STOP) {
+	if (SI_EVENT(si.si_code) != PTRACE_EVENT_STOP) {
 		/*
 		 * Kernel notifies us about the task being seized received some
 		 * event other than the STOP, i.e. -- a signal. Let the task