xsplice/xen_replace_world: Test-case for XSPLICE_ACTION_REPLACE

With this third payload one can do:

-bash-4.1# xen-xsplice load xen_hello_world.xsplice
Uploading xen_hello_world.xsplice (10148 bytes)
Performing check: completed
Performing apply:. completed

[xen_hello_world depends on hypervisor build-id]
-bash-4.1# xen-xsplice load xen_bye_world.xsplice
Uploading xen_bye_world.xsplice (7076 bytes)
Performing check: completed
Performing apply:. completed
[xen_bye_world depends on xen_hello_world build-id]
-bash-4.1# xen-xsplice upload xen_replace_world xen_replace_world.xsplice
Uploading xen_replace_world.xsplice (7148 bytes)
-bash-4.1# xen-xsplice list
 ID                                     | status
----------------------------------------+------------
xen_hello_world                         | APPLIED
xen_bye_world                           | APPLIED
xen_replace_world                       | CHECKED
-bash-4.1# xen-xsplice replace xen_replace_world
Performing replace:. completed
-bash-4.1# xl info | grep extra
xen_extra              : Hello Again World!
-bash-4.1# xen-xsplice list
 ID                                     | status
----------------------------------------+------------
xen_hello_world                         | CHECKED
xen_bye_world                           | CHECKED
xen_replace_world                       | APPLIED

and revert both of the previous payloads and apply
the xen_replace_world.

All the magic of this is in the Makefile - we extract
the build-id from the hypervisor (xen-syms) and jam it
in the xen_replace_world as .xsplice.depends.

We also make .old_addr be zero, forcing the hypervisor
to lookup the xen_extra_version.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>

.gitignore

@@ -249,6 +249,7 @@ xen/arch/x86/efi/mkreloc
 xen/arch/x86/test/config.h
 xen/arch/x86/test/xen_hello_world.xsplice
 xen/arch/x86/test/xen_bye_world.xsplice
+xen/arch/x86/test/xen_replace_world.xsplice
 xen/arch/*/efi/boot.c
 xen/arch/*/efi/compat.c
 xen/arch/*/efi/efi.h

xen/arch/x86/test/Makefile

@@ -7,15 +7,18 @@ CODE_SZ=$(shell nm --defined -S $(1) | grep $(2) | awk '{ print "0x"$$2}')
 
 XSPLICE := xen_hello_world.xsplice
 XSPLICE_BYE := xen_bye_world.xsplice
+XSPLICE_REPLACE := xen_replace_world.xsplice
 
 default: xsplice
 
 install: xsplice
 	$(INSTALL_DATA) $(XSPLICE) $(DESTDIR)$(DEBUG_DIR)/$(XSPLICE)
 	$(INSTALL_DATA) $(XSPLICE_BYE) $(DESTDIR)$(DEBUG_DIR)/$(XSPLICE_BYE)
+	$(INSTALL_DATA) $(XSPLICE_REPLACE) $(DESTDIR)$(DEBUG_DIR)/$(XSPLICE_REPLACE)
 uninstall:
 	rm -f $(DESTDIR)$(DEBUG_DIR)/$(XSPLICE)
 	rm -f $(DESTDIR)$(DEBUG_DIR)/$(XSPLICE_BYE)
+	rm -f $(DESTDIR)$(DEBUG_DIR)/$(XSPLICE_REPLACE)
 
 .PHONY: clean
 clean::
@@ -72,5 +75,11 @@ xen_bye_world.o: config.h
 $(XSPLICE_BYE): xen_bye_world_func.o xen_bye_world.o hello_world_note.o
 	$(LD) $(LDFLAGS) $(build_id_linker) -r -o $(XSPLICE_BYE) $^
 
+xen_replace_world.o: config.h
+
+.PHONY: $(XSPLICE_REPLACE)
+$(XSPLICE_REPLACE): xen_replace_world_func.o xen_replace_world.o note.o
+	$(LD) $(LDFLAGS) $(build_id_linker) -r -o $(XSPLICE_REPLACE) $^
+
 .PHONY: xsplice
-xsplice: $(XSPLICE) $(XSPLICE_BYE)
+xsplice: $(XSPLICE) $(XSPLICE_BYE) $(XSPLICE_REPLACE)

xen/arch/x86/test/xen_replace_world.c

@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2016 Oracle and/or its affiliates. All rights reserved.
+ *
+ */
+
+#include "config.h"
+#include <xen/lib.h>
+#include <xen/types.h>
+#include <xen/xsplice.h>
+
+#include <public/sysctl.h>
+
+static char xen_replace_world_name[] = "xen_extra_version";
+extern const char *xen_replace_world(void);
+
+struct xsplice_patch_func __section(".xsplice.funcs") xsplice_xen_replace_world = {
+    .version = XSPLICE_PAYLOAD_VERSION,
+    .name = xen_replace_world_name,
+    .old_addr = 0, /* Forces the hypervisor to lookup .name */
+    .new_addr = xen_replace_world,
+    .new_size = NEW_CODE_SZ,
+    .old_size = OLD_CODE_SZ,
+};
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */

xen/arch/x86/test/xen_replace_world_func.c

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2016 Oracle and/or its affiliates. All rights reserved.
+ *
+ */
+
+#include <xen/types.h>
+
+/* Our replacement function for xen_hello_world. */
+const char *xen_replace_world(void)
+{
+    return "Hello Again World!";
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */