diff --git a/CONFIG.example b/CONFIG.example
index 5facb632..9caa3c5e 100644
--- a/CONFIG.example
+++ b/CONFIG.example
@@ -3,12 +3,14 @@
 # Copy this file to CONFIG and edit the settings below to suit your
 # environment.
 
-# Location of rootfs builder.  This needs to be at least version 1.10 and can be
+# Location of rootfs builder.  This needs to be at least version 1.13 and can be
 # downloaded from https://github.com/araneidae/rootfs
-ROOTFS_TOP = /dls_sw/prod/targetOS/rootfs/1-10
+ROOTFS_TOP = /dls_sw/prod/targetOS/rootfs/1.13
 
-# Location of SDK used to build target
-SDK_ROOT = /dls_sw/apps/FPGA/Xilinx/SDK/2015.1
+# Location of SDK used to build target.  There are a couple of ways that this
+# can be specified, depending on precisely where the toolchain is installed.
+# The simplest option is to specify SDK_ROOT.
+SDK_ROOT = /dls_sw/apps/FPGA/Xilinx/SDK/2016.4
 
 # Where to find source files
 TAR_FILES = /dls_sw/prod/targetOS/tar-files
diff --git a/Makefile b/Makefile
index 2e05d721..959a387e 100644
--- a/Makefile
+++ b/Makefile
@@ -15,10 +15,8 @@ MD5_SUM_linux-xlnx-xilinx-v2015.1  = 930d126df2113221e63c4ec4ce356f2c
 SPHINX_BUILD = sphinx-build
 
 # Locations of key files in the SDK
-BOOTGEN = $(SDK_ROOT)/bin/bootgen
-BINUTILS_DIR = $(SDK_ROOT)/gnu/arm/lin/bin
 # Cross-compilation tuple for toolkit
-CROSS_COMPILE = arm-xilinx-linux-gnueabi-
+COMPILER_PREFIX = arm-xilinx-linux-gnueabi
 
 # The final boot image is assembled here
 BOOT_IMAGE = $(PANDA_ROOT)/boot
@@ -35,8 +33,20 @@ KERNEL_TAG = xilinx-v2015.1
 # Configuration and local settings.
 include CONFIG
 
+
+CROSS_COMPILE = $(COMPILER_PREFIX)-
+
+ifdef SDK_ROOT
+    BOOTGEN ?= $(SDK_ROOT)/bin/bootgen
+    BINUTILS_DIR ?= $(SDK_ROOT)/gnu/arm/lin
+endif
+
+ifdef BINUTILS_DIR
+    SYSROOT ?= $(BINUTILS_DIR)/$(COMPILER_PREFIX)/libc
+endif
+
 # We'll check that these symbols have been defined.
-REQUIRED_SYMBOLS = ROOTFS_TOP SDK_ROOT TAR_FILES PANDA_ROOT
+REQUIRED_SYMBOLS = ROOTFS_TOP BOOTGEN BINUTILS_DIR SYSROOT TAR_FILES PANDA_ROOT
 
 
 default: boot
@@ -54,7 +64,7 @@ BOOT_BUILD = $(BUILD_ROOT)/boot
 
 U_BOOT_TOOLS = $(U_BOOT_BUILD)/tools
 
-export PATH := $(BINUTILS_DIR):$(U_BOOT_TOOLS):$(PATH)
+export PATH := $(BINUTILS_DIR)/bin:$(U_BOOT_TOOLS):$(PATH)
 
 
 # ------------------------------------------------------------------------------
@@ -216,6 +226,7 @@ u-boot-src: $(U_BOOT_SRC)
 
 # Command for building rootfs.  Need to specify both action and target name.
 MAKE_ROOTFS = \
+    $(call EXPORT,COMPILER_PREFIX SYSROOT) \
     $(ROOTFS_TOP)/rootfs -f '$(TAR_FILES)' -r $(PANDA_ROOT) -t $(CURDIR)/$1 $2
 
 %.gz: %
diff --git a/docs/building.rst b/docs/building.rst
index 27a0a50d..51aae08e 100644
--- a/docs/building.rst
+++ b/docs/building.rst
@@ -53,6 +53,25 @@ and modify the following fields as required:
     This needs to point to the root directory of the Diamond rootfs builder,
     download from the github location given above.
 
+Three files and directories are taken from ``SDK_ROOT``, and they can instead be
+specified directly.  Note that in this case ``SDK_ROOT`` must *not* be set.
+
+``BOOTGEN``
+    This is the path to a Xilinx toolchain tool used to build the ``boot.bin``
+    file.  By default this is set to ``$(SDK_ROOT)/bin/bootgen``.
+
+``BINUTILS_DIR``
+    This is the path to the gcc cross-compiler toolchain to use.  By default
+    this is set to ``$(SDK_ROOT)/gnu/arm/lin``.  The directory
+    ``$(BINUTILS_DIR)/bin`` will be added to the path during the build.
+
+``SYSROOT``
+    This is the path to the compiled system root (derived from libc).  Normally
+    this is part of the installed toolchain, and if not set elsewhere this is
+    set to ``$(BINUTILS_DIR)/$(COMPILER_PREFIX)/libc``.
+
+Note that the ``COMPILER_PREFIX`` symbol can also be overwritten if required.
+The default value is ``arm-xilinx-linux-gnueabi``.
 
 Sources
 ~~~~~~~
diff --git a/initramfs/CONFIG b/initramfs/CONFIG
index 2737abfb..7fedb958 100644
--- a/initramfs/CONFIG
+++ b/initramfs/CONFIG
@@ -1,8 +1,6 @@
 # Kernel initramfs definition.  This is a minimal image with just enough to do
 # what we need to prepare to run the true system.
 
-TOOLCHAIN = xlnx-zynq
-
 PACKAGES += busybox
 busybox_VERSION = 1.23.2
 busybox_CONFIG = $(configdir)/busybox.config
diff --git a/rootfs/CONFIG b/rootfs/CONFIG
index ac31a4d1..57d2b088 100644
--- a/rootfs/CONFIG
+++ b/rootfs/CONFIG
@@ -2,7 +2,6 @@
 
 # -----------------------------------------------------------------------------
 # Package definitions for Zynq
-TOOLCHAIN = xlnx-zynq
 
 PACKAGES += busybox
 busybox_VERSION = 1.23.2