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

build-xen

@@ -1,39 +1,42 @@
 #!/usr/bin/env bash
-# TODO get working, aarch64 Xen integration attempt.
-# Current state: prints to Boot-wrapper v0.2 to screen and hangs.
-# Bibliography:
-# https://wiki.xenproject.org/wiki/Xen_ARM_with_Virtualization_Extensions/qemu-system-aarch64
-# https://blog.xenproject.org/2014/04/01/virtualization-on-arm-with-xen/
+# https://github.com/cirosantilli/linux-kernel-module-cheat#xen
 set -eux
 cd submodules/xen
 make \
   -j `nproc` \
   dist-xen \
   CONFIG_DEBUG=y \
-  CONFIG_EARLY_PRINTK=vexpress \
+  CONFIG_EARLY_PRINTK=pl011,0x09000000 \
   CROSS_COMPILE=aarch64-linux-gnu- \
   XEN_TARGET_ARCH=arm64 \
 ;
 cd ../boot-wrapper-aarch64
-autoreconf -i
 ../../out/qemu/default/aarch64-softmmu/qemu-system-aarch64 \
   -machine virt \
   -machine virtualization=on \
+  -machine gic_version=3 \
+  -cpu cortex-a57 \
+  -kernel xen-system.axf \
+  -serial mon:stdio \
+  -nographic \
   -machine dumpdtb=dtb.dtb \
 ;
+autoreconf -i
 ./configure \
   --enable-gicv3 \
   --enable-psci \
   --host=aarch64-linux-gnu \
-  --with-cmdline="console=hvc0 root=/dev/vda rw mem=1G" \
+  --with-cmdline="console=hvc0 earlycon=pl011,0x09000000 root=/dev/vda rw" \
   --with-dtb=dtb.dtb \
   --with-kernel-dir=../../out/linux/default/aarch64 \
-  --with-xen-cmdline="dtuart=/uart@1c090000 console=dtuart no-bootscrub dom0_mem=1G loglvl=all guest_loglvl=all" \
+  --with-xen-cmdline="dtuart=/pl011,0x09000000 console=dtuart no-bootscrub dom0_mem=512M loglvl=all guest_loglvl=all" \
   --with-xen=../xen/xen/xen \
 ;
+make -j `nproc`
 ../../out/qemu/default/aarch64-softmmu/qemu-system-aarch64 \
-  -M virt \
-  -M virtualization=on \
+  -machine virt \
+  -machine virtualization=on \
+  -machine gic_version=3 \
   -cpu cortex-a57 \
   -kernel xen-system.axf \
   -serial mon:stdio \