From b4283c91215a851a73be25415fea7f8156799e59 Mon Sep 17 00:00:00 2001
From: Alexander Boettcher <alexander.boettcher@genode-labs.com>
Date: Fri, 5 Jul 2013 11:44:55 +0200
Subject: [PATCH] seoul: use utcb guard

Forgetting to restore the old utcb content results in hard to debug bugs.
Save only the amount of word items which are actually on the UTCB.

Issue #806
---
 ports/src/vancouver/disk.cc      |  6 ++--
 ports/src/vancouver/utcb_guard.h | 55 ++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+), 4 deletions(-)
 create mode 100644 ports/src/vancouver/utcb_guard.h

diff --git a/ports/src/vancouver/disk.cc b/ports/src/vancouver/disk.cc
index b6ae300a4..46a4e81bb 100644
--- a/ports/src/vancouver/disk.cc
+++ b/ports/src/vancouver/disk.cc
@@ -28,6 +28,7 @@
 
 /* local includes */
 #include <disk.h>
+#include <utcb_guard.h>
 
 static Genode::Native_utcb utcb_backup;
 
@@ -67,7 +68,7 @@ void Vancouver_disk::entry()
 
 bool Vancouver_disk::receive(MessageDisk &msg)
 {
-	utcb_backup = *Genode::Thread_base::myself()->utcb();
+	Utcb_guard guard(utcb_backup);
 
 	if (msg.disknr >= MAX_DISKS)
 		Logging::panic("You configured more disks than supported.\n");
@@ -125,7 +126,6 @@ bool Vancouver_disk::receive(MessageDisk &msg)
 				MessageDiskCommit ro(msg.disknr, msg.usertag,
 				                     MessageDisk::DISK_STATUS_DEVICE);
 				_motherboard()->bus_diskcommit.send(ro);
-				*Genode::Thread_base::myself()->utcb() = utcb_backup;
 				return true;
 			}
 
@@ -207,10 +207,8 @@ bool Vancouver_disk::receive(MessageDisk &msg)
 	default:
 
 		Logging::printf("Got MessageDisk type %x\n", msg.type);
-		*Genode::Thread_base::myself()->utcb() = utcb_backup;
 		return false;
 	}
-	*Genode::Thread_base::myself()->utcb() = utcb_backup;
 	return true;
 }
 
diff --git a/ports/src/vancouver/utcb_guard.h b/ports/src/vancouver/utcb_guard.h
new file mode 100644
index 000000000..4986cf6af
--- /dev/null
+++ b/ports/src/vancouver/utcb_guard.h
@@ -0,0 +1,55 @@
+/*
+ * \brief  Guard to save a utcb and restore it during Guard desctruction
+ * \author Alexander Boettcher
+ * \date   2013-07-05
+ */
+
+/*
+ * Copyright (C) 2013 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU General Public License version 2.
+ */
+
+#ifndef _SEOUL_UTCB_GUARD_H_
+#define _SEOUL_UTCB_GUARD_H_
+
+#include <base/printf.h>
+#include <nova/syscalls.h>
+
+class Utcb_guard {
+
+	private:
+		Genode::Native_utcb &_backup_utcb;
+
+	public:
+
+		Utcb_guard(Genode::Native_utcb &backup_utcb)
+		: _backup_utcb(backup_utcb)
+		{
+			using namespace Genode;
+	
+			Nova::Utcb *utcb =
+				reinterpret_cast<Nova::Utcb *>(Thread_base::myself()->utcb());
+
+			unsigned header_len = (char *)utcb->msg - (char *)utcb;
+			unsigned len = header_len + utcb->msg_words() * sizeof(Nova::mword_t);
+			Genode::memcpy(&_backup_utcb, utcb, len);
+
+			if (utcb->msg_items())
+				PWRN("Error: msg items on UTCB are not saved and restored !!!");
+		}
+
+		~Utcb_guard()
+		{
+			using namespace Genode;
+
+			Nova::Utcb *utcb = reinterpret_cast<Nova::Utcb *>(&_backup_utcb);
+
+			unsigned header_len = (char *)utcb->msg - (char *)utcb;
+			unsigned len = header_len + utcb->msg_words() * sizeof(Nova::mword_t);
+			Genode::memcpy(Thread_base::myself()->utcb(), utcb, len);
+		}
+};
+
+#endif /* _SEOUL_UTCB_GUARD_H_ */