zdtm/sigpending/32: check only 12 bytes of _si_fields

The kernel does touch only relevant union member on x86_32.

travis-ci: success for zdtm/sigpending/32: check only 12 bytes of _si_fields
Cc: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

test/zdtm/static/sigpending.c

@@ -29,6 +29,26 @@ static int thread_nr;
 # define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
 #endif
 
+#ifdef __i386__
+/*
+ * On x86_32 kernel puts only relevant union member when signal arrives,
+ * leaving _si_fields to be filled with junk from stack. Check only
+ * first 12 bytes:
+ *	// POSIX.1b signals.
+ *	struct
+ *	  {
+ *	    __pid_t si_pid;	// Sending process ID.
+ *	    __uid_t si_uid;	// Real user ID of sending process.
+ *	    sigval_t si_sigval;	// Signal value.
+ *	  } _rt;
+ * Look at __copy_siginfo_to_user32() for more information.
+ */
+# define _si_fields_sz 12
+#else
+# define _si_fields_sz (sizeof(siginfo_t) - offsetof(siginfo_t, _sifields))
+#endif
+#define siginfo_filled (offsetof(siginfo_t, _sifields) + _si_fields_sz)
+
 static pthread_mutex_t exit_lock;
 static pthread_mutex_t init_lock;
 
@@ -71,13 +91,12 @@ static void sig_handler(int signal, siginfo_t *info, void *data)
 		}
 
 		crc = ~0;
-		if (datachk((uint8_t *) &info->_sifields,
-			    sizeof(siginfo_t) - offsetof(siginfo_t, _sifields), &crc)) {
+		if (datachk((uint8_t *) &info->_sifields, _si_fields_sz, &crc)) {
 			fail("CRC mismatch\n");
 			return;
 		}
 
-		 if (memcmp(info, src, sizeof(siginfo_t))) {
+		 if (memcmp(info, src, siginfo_filled)) {
 			fail("Source and received info are differ\n");
 			return;
 		}
@@ -154,8 +173,7 @@ int send_siginfo(int signo, pid_t pid, pid_t tid, int group, siginfo_t *info)
 	info->si_code = si_code;
 	si_code--;
 	info->si_signo = signo;
-	datagen((uint8_t *) &info->_sifields,
-		    sizeof(siginfo_t) - offsetof(siginfo_t, _sifields), &crc);
+	datagen((uint8_t *) &info->_sifields, _si_fields_sz, &crc);
 
 	sent_sigs++;