Now we save/restore utcb registers if we do a second ipc before returning the first.

tasks/fs0/src/syscalls.c

@@ -30,6 +30,8 @@ int pager_sys_open(l4id_t sender, int fd, unsigned long vnum, unsigned long size
 {
 	int err;
 
+	l4_save_ipcregs();
+
 	write_mr(L4SYS_ARG0, sender);
 	write_mr(L4SYS_ARG1, fd);
 	write_mr(L4SYS_ARG2, vnum);
@@ -46,6 +48,7 @@ int pager_sys_open(l4id_t sender, int fd, unsigned long vnum, unsigned long size
 		printf("%s: Pager open Error: %d.\n", __FUNCTION__, fd);
 		return err;
 	}
+	l4_restore_ipcregs();
 
 	return 0;
 }

tasks/libl4/include/l4lib/arch-arm/syslib.h

@@ -38,6 +38,17 @@ static inline l4id_t l4_get_sender(void)
 	return (l4id_t)read_mr(MR_SENDER);
 }
 
+/*
+ * When doing an ipc the sender never has to be explicitly set in
+ * the utcb via this function since it is passed in the argument
+ * registers. This is only used for restoring the sender on the
+ * utcb in order to complete an earlier ipc.
+ */
+static inline void l4_set_sender(l4id_t sender)
+{
+	write_mr(MR_SENDER, sender);
+}
+
 static inline unsigned int l4_get_tag(void)
 {
 	return read_mr(MR_TAG);
@@ -48,6 +59,23 @@ static inline void l4_set_tag(unsigned int tag)
 	write_mr(MR_TAG, tag);
 }
 
+/*
+ * If we're about to do another ipc, this saves the last ipc's
+ * parameters such as the sender and tag information.
+ * Any previously saved data in save slots are destroyed.
+ */
+static inline void l4_save_ipcregs(void)
+{
+	l4_get_utcb()->saved_sender = l4_get_sender();
+	l4_get_utcb()->saved_tag = l4_get_tag();
+}
+
+static inline void l4_restore_ipcregs(void)
+{
+	l4_set_tag(l4_get_utcb()->saved_tag);
+	l4_set_sender(l4_get_utcb()->saved_sender);
+}
+
 static inline l4id_t self_tid(void)
 {
 	struct task_ids ids;

tasks/libl4/include/l4lib/arch-arm/utcb.h

@@ -25,7 +25,8 @@
  */
 struct utcb {
 	u32 mr[MR_TOTAL];
-	u32 tid;		/* Thread id */
+	u32 saved_tag;
+	u32 saved_sender;
 } __attribute__((__packed__));
 
 extern struct utcb utcb;