xen: document failed attempt

README.adoc

@@ -8550,9 +8550,9 @@ kill %1
 
 `stress -c 1 -t 1` makes gem5 irresponsive for a very long time.
 
-== Linux kernel build system
+=== Linux kernel build system
 
-=== vmlinux vs bzImage vs zImage vs Image
+==== vmlinux vs bzImage vs zImage vs Image
 
 Between all archs on QEMU and gem5 we touch all of those kernel built output files.
 
@@ -8571,6 +8571,38 @@ as mentioned at:
 * https://unix.stackexchange.com/questions/352215/how-do-i-extract-vmlinux-from-an-arm-image
 * https://raspberrypi.stackexchange.com/questions/88621/why-doesnt-extract-vmlinux-work-with-raspbians-boot-kernel-img
 
+== Xen
+
+TODO: get prototype working and then properly integrate:
+
+....
+./build-xen
+....
+
+Source: link:build-xen[]
+
+This script attempts to build Xen for aarch64 and feed it into QEMU through link:boot-wrapper-arch64[]
+
+The current bad behaviour is that it prints just:
+
+....
+Boot-wrapper v0.2
+....
+
+and nothing else.
+
+We will also need `CONFIG_XEN=y` on the Linux kernel, but first Xen should print some Xen messages before the kernel is ever reached.
+
+If we pass to QEMU the xen image directly instead of the boot wrapper one:
+
+....
+-kernel ../xen/xen/xen
+....
+
+then Xen messages do show up, so it seems that the configuration failure lies in the boot wrapper itself rather than Xen.
+
+Bibliography: this attempt was based on: https://wiki.xenproject.org/wiki/Xen_ARM_with_Virtualization_Extensions/FastModels which is the documentation for the ARM Fast Models closed source simulators.
+
 == QEMU
 
 === Introduction to QEMU