A script to build XNU version 4570.41.2 (macOS High Sierra 10.13.3) on macOS 10.13.5 with Xcode 9.4.

build-xnu-4570.41.2.sh

#! /bin/bash
#
# build-xnu-4570.41.2.sh
# Brandon Azad
#
# A script showing how to build XNU version 4570.41.2 on macOS High Sierra
# 10.13.5 with Xcode 9.4.
#
# Note: This process will OVERWRITE files in Xcode's MacOSX10.13.sdk. Make a
# backup of this directory first!
#

XNU="xnu-4570.41.2"
DTRACE="dtrace-262"
AVAILABILITY_VERSIONS="AvailabilityVersions-32.30.1"
LIBPLATFORM="libplatform-161.20.1"
LIBDISPATCH="libdispatch-913.30.4"

# Set the working directory.
WORKDIR="${WORKDIR:-build-${XNU}}"

# Set a permissive umask just in case.
umask 022

# Print commands and exit on failure.
set -ex

# Get the SDK path and toolchain path.
SDKPATH="$(xcrun --sdk macosx --show-sdk-path)"
TOOLCHAINPATH="$(xcode-select -p)/Toolchains/XcodeDefault.xctoolchain"
[ -d "${SDKPATH}" ] && [ -d "${TOOLCHAINPATH}" ]

# Create the working directory.
mkdir "${WORKDIR}"
cd "${WORKDIR}"

# Back up the SDK if that option is given.
SDK_DIR="$(basename ${SDKPATH})"
if [ -n "${BACKUP_SDK}" ] && ! [ -e "${SDK_DIR}" ]; then
	sudo ditto "${SDKPATH}" "${SDK_DIR}"
fi

# Download XNU and some additional sources we will need to help build.
curl https://opensource.apple.com/tarballs/xnu/${XNU}.tar.gz | tar -xf-
curl https://opensource.apple.com/tarballs/dtrace/${DTRACE}.tar.gz | tar -xf-
curl https://opensource.apple.com/tarballs/AvailabilityVersions/${AVAILABILITY_VERSIONS}.tar.gz | tar -xf-
curl https://opensource.apple.com/tarballs/libplatform/${LIBPLATFORM}.tar.gz | tar -xf-
curl https://opensource.apple.com/tarballs/libdispatch/${LIBDISPATCH}.tar.gz | tar -xf-

# Build and install ctf utilities. This adds the ctf tools to
# ${TOOLCHAINPATH}/usr/local/bin.
cd ${DTRACE}
mkdir -p obj dst sym
xcodebuild install -target ctfconvert -target ctfdump -target ctfmerge ARCHS="x86_64" SRCROOT="${PWD}" OBJROOT="${PWD}/obj" SYMROOT="${PWD}/sym" DSTROOT="${PWD}/dst"
# TODO: Get the XcodeDefault.toolchain path programmatically.
sudo ditto "${PWD}/dst/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain" "${TOOLCHAINPATH}"
cd ..

# Install AvailabilityVersions. This writes to ${SDKPATH}/usr/local/libexec.
cd ${AVAILABILITY_VERSIONS}
mkdir -p dst
make install SRCROOT="${PWD}" DSTROOT="${PWD}/dst"
sudo ditto "${PWD}/dst/usr/local" "${SDKPATH}/usr/local"
cd ..

# Install the XNU headers we'll need for libdispatch. This OVERWRITES files in
# MacOSX10.13.sdk!
cd ${XNU}
mkdir -p BUILD.hdrs/obj BUILD.hdrs/sym BUILD.hdrs/dst
make installhdrs SDKROOT=macosx ARCH_CONFIGS=X86_64 SRCROOT="${PWD}" OBJROOT="${PWD}/BUILD.hdrs/obj" SYMROOT="${PWD}/BUILD.hdrs/sym" DSTROOT="${PWD}/BUILD.hdrs/dst"
# HACK: The subsequent build command fails with a missing file error. We create
# that file so that the build continues.
touch libsyscall/os/thread_self_restrict.h
xcodebuild installhdrs -project libsyscall/Libsyscall.xcodeproj -sdk macosx ARCHS="x86_64 i386" SRCROOT="${PWD}/libsyscall" OBJROOT="${PWD}/BUILD.hdrs/obj" SYMROOT="${PWD}/BUILD.hdrs/sym" DSTROOT="${PWD}/BUILD.hdrs/dst"
# Set permissions correctly before dittoing over MacOSX10.13.sdk.
sudo chown -R root:wheel BUILD.hdrs/dst/
sudo ditto BUILD.hdrs/dst "${SDKPATH}"
cd ..

# Install libplatform headers to ${SDKPATH}/usr/local/include.
cd ${LIBPLATFORM}
sudo ditto "${PWD}/include" "${SDKPATH}/usr/local/include"
sudo ditto "${PWD}/private"  "${SDKPATH}/usr/local/include"
cd ..

# Build and install libdispatch's libfirehose_kernel target to
# ${SDKPATH}/usr/local.
cd ${LIBDISPATCH}
mkdir -p obj sym dst
xcodebuild install -project libdispatch.xcodeproj -target libfirehose_kernel -sdk macosx ARCHS="x86_64 i386" SRCROOT="${PWD}" OBJROOT="${PWD}/obj" SYMROOT="${PWD}/sym" DSTROOT="${PWD}/dst"
sudo ditto "${PWD}/dst/usr/local" "${SDKPATH}/usr/local"
cd ..

# Patch XNU. This corrects a build error and removes an annoying warning.
cat <<"EOF" > ${XNU}.patch
diff --git a/makedefs/MakeInc.def b/makedefs/MakeInc.def
index 8c49bd7..87044b9 100644
--- a/makedefs/MakeInc.def
+++ b/makedefs/MakeInc.def
@@ -149,6 +149,7 @@ WARNFLAGS_STD := \
 	-Wno-used-but-marked-unused \
 	-Wno-variadic-macros \
 	-Wno-vla \
+	-Wno-zero-as-null-pointer-constant \
 	-Wno-zero-length-array
 
 CWARNFLAGS_STD = \
diff --git a/osfmk/i386/cpu_topology.c b/osfmk/i386/cpu_topology.c
index e079e6e..5280788 100644
--- a/osfmk/i386/cpu_topology.c
+++ b/osfmk/i386/cpu_topology.c
@@ -26,6 +26,7 @@
  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  */
 
+#include <stddef.h>
 #include <mach/machine.h>
 #include <mach/processor.h>
 #include <kern/kalloc.h>
EOF
cd ${XNU}
patch -p1 < ../${XNU}.patch
cd ..

# Build XNU. We set BUILD_WERROR to 0 to disable -Werror during build, since
# XNU definitely does not build without errors.
cd ${XNU}
make SDKROOT=macosx ARCH_CONFIGS=X86_64 KERNEL_CONFIGS="RELEASE" BUILD_WERROR=0