On 01/14/2016 09:47 PM, Konrad Rzeszutek Wilk wrote:
This change demonstrates how to generate an xSplice ELF payload.
The idea here is that we want to patch in the hypervisor
the 'xen_version_extra' function with an function that will
return 'Hello World'. The 'xl info | grep extraversion'
will reflect the new value after the patching.
snip
+### Example
+
+A simple example of what a payload file can be:
+
+<pre>
+/* MUST be in sync with hypervisor. */
+struct xsplice_patch_func {
+ const char *name;
+ unsigned long new_addr;
+ const unsigned long old_addr;
+ uint32_t new_size;
+ const uint32_t old_size;
+ uint8_t pad[32];
+};
+
+/* Our replacement function for xen_extra_version. */
+const char *xen_hello_world(void)
+{
+ return "Hello World";
+}
+
+struct xsplice_patch_func xsplice_hello_world = {
+ .name = "xen_extra_version",
+ .new_addr = &xen_hello_world,
+ .old_addr = 0xffff82d08013963c, /* Extracted from xen-syms. */
+ .new_size = 13, /* To be be computed by scripts. */
+ .old_size = 13, /* -----------""--------------- */
+};
+</pre>
+
+With the linker script as follow to change the `xsplice_hello_world`
+do be `.xsplice.funcs` :
+
+<pre>
+OUTPUT_FORMAT("elf64-x86-64", "elf64-x86-64", "elf64-x86-64")
+OUTPUT_ARCH(i386:x86-64)
+ENTRY(xsplice_hello_world)
+SECTIONS
+{
+ /* The hypervisor expects ".xsplice.func", so change
+ * the ".data.xsplice_hello_world" to it. */
+
+ .xsplice.funcs : { *(*.xsplice_hello_world) }
+ }
+}
+</pre>
You should be able to use __attribute__((__section__(".xsplice.funcs")))
on the structure to avoid needing to use a linker script.
+
+Code must be compiled with -fPIC.
+
## Hypercalls
We will employ the sub operations of the system management hypercall (sysctl).
diff --git a/tools/misc/Makefile b/tools/misc/Makefile
index c46873e..8385830 100644
--- a/tools/misc/Makefile
+++ b/tools/misc/Makefile
@@ -36,6 +36,10 @@ INSTALL_SBIN += $(INSTALL_SBIN-y)
# Everything to be installed in a private bin/
INSTALL_PRIVBIN += xenpvnetboot
+# We need the hypervisor - and only 64-bit builds have it.
+ifeq ($(XEN_COMPILE_ARCH),x86_64)
+INSTALL_PRIVBIN += xen_hello_world.xsplice
+endif
# Everything to be installed
TARGETS_ALL := $(INSTALL_BIN) $(INSTALL_SBIN) $(INSTALL_PRIVBIN)
@@ -49,7 +53,7 @@ TARGETS_COPY += xenpvnetboot
# Everything which needs to be built
TARGETS_BUILD := $(filter-out $(TARGETS_COPY),$(TARGETS_ALL))
-.PHONY: all build
+.PHONY: all build xsplice
all build: $(TARGETS_BUILD)
.PHONY: install
@@ -111,4 +115,23 @@ gtraceview: gtraceview.o
xencov: xencov.o
$(CC) $(LDFLAGS) -o $@ $< $(LDLIBS_libxenctrl) $(APPEND_LDFLAGS)
+.PHONY: xsplice
+xsplice:
+ifeq ($(XEN_COMPILE_ARCH),x86_64)
+ # We MUST regenerate the file everytime we build - in case the
hypervisor
+ # is rebuilt too.
+ $(RM) *.xplice
+ $(MAKE) xen_hello_world.xsplice
Can't you depend on xen-syms to avoid recompiling this every time.
+endif
+
+XEN_EXTRA_VERSION_ADDR=$(shell nm --defined $(XEN_ROOT)/xen/xen-syms | grep
xen_extra_version | awk '{print "0x"$$1}')
+
+xen_hello_world.xsplice: xen_hello_world.c
+ $(CC) -DOLD_CODE=$(XEN_EXTRA_VERSION_ADDR) -I$(XEN_ROOT)/tools/include \
+ -fPIC -Wl,--emit-relocs \
+ -Wl,-r -Wl,--entry=xsplice_hello_world \
+ -fdata-sections -ffunction-sections \
+ -nostdlib -Txsplice.lds \
+ -o $@ $<
+ @objdump -x --section=.xsplice.funcs $@
If you use __attribute__((__section__(".xsplice.funcs"))) on the struct,
you can drop the custom linker script and simplify the command-line to
something like:
$(CC) -DOLD_CODE=$(XEN_EXTRA_VERSION_ADDR) -I$(XEN_ROOT)/tools/include \
-c -o $@ $< $(CFLAGS)
Having mostly the same CFLAGS that Xen uses is important because it
contains things like -mno-red-zone, -fno-asynchronous-unwind-tables, and
-mno-sse, etc which affect the way the code is compiled.
--
Ross Lagerwall
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