Update GEM5 to master to fix x86 boot via 3feeb994ae613fd6b3734c1a991285b2ecbd1946

See also: http://gem5-users.gem5.narkive.com/CQh9J6fU/fail-to-run-fs-mode-with-linux-kernel-v4-8-13-and-ubuntu-image-16-04-1

Start sketching how to tweak system parameters, number of CPUs works, caches don't.

build

@@ -48,16 +48,7 @@ case "$arch" in
     defconfig=qemu_x86_64_defconfig
   ;;
   arm)
-    if "$gem5"; then
-      # Ideally we should use a custom clean config here.
-      # But let's just use this one as a starting point for now.
-      defconfig=qemu_arm_versatile_defconfig
-      post_script_args="$post_script_args -n"
-    else
-      # qemu_arm_vexpress_defconfig required a newer QEMU than 2.0.0 on a Ubuntu host.
-      # so let's stick to versatile for now.
-      defconfig=qemu_arm_versatile_defconfig
-    fi
+    defconfig=qemu_arm_versatile_defconfig
   ;;
   aarch64)
     defconfig=qemu_aarch64_virt_defconfig
@@ -69,6 +60,8 @@ esac
 arch_dir="$arch"
 if "$gem5"; then
   arch_dir="${arch}-gem5"
+  # Networking was not working, so disable it to speed things up.
+  post_script_args="$post_script_args -n"
 fi
 
 cd kernel_module