#/bin/bash

# kpatch build script for Fedora

# This script takes a patch based on the version of the kernel
# currently running and creates a kernel module that will
# replace modified functions in the kernel such that the
# patched code takes effect.

# This script contains Fedora specific nuances and will probably
# not work on other distributions; however, it does serve as a tutorial
# on the various steps involved and should be adaptable to other
# distributions.

# This script:
# - Installs the required yum/rpm tools
# - Downloads the kernel src rpm for the currently running kernel
# - Installs the build dependencies for the src rpm
# - Unpacks and prepares the src rpm for building
# - Builds the base kernel (vmlinux)
# - Builds the patched kernel and monitors changed objects
# - Builds the patched objects with gcc flags -f[function|data]-sections
# - Runs kpatch tools to create and link the patch kernel module

BASE=$PWD
LOGFILE=$PWD/kpatch-build.log
KPATCHPATH=/usr/local/share/kpatch
ARCHVERSION=$(uname -r)
DISTROVERSION=${ARCHVERSION%*.*}
CPUS=$(grep -c ^processor /proc/cpuinfo)
LOCALVERSION=$(uname -r)
LOCALVERSION=-${LOCALVERSION##*-}

cleanup() {
	rm -Rf kernel-$DISTROVERSION.src.rpm rpmbuild $LOGFILE $TEMPDIR > /dev/null 2>/dev/null
}

die() {
	echo "kpatch encountered an error"
	exit 1
}

if [ $# -ne 1 ]
then
	echo "kpatch patchfile"
	exit 2
fi

PATCHFILE=$(readlink -f $1)
if [ ! -e $PATCHFILE ]
then
	echo "patch file not found"
	exit 3
fi

cleanup

echo "Verifying required development tools"
yum install rpmdevtools yum-utils || die

echo "Downloading kernel source for $ARCHVERSION"
yumdownloader --source kernel-$ARCHVERSION || die

echo "Verifying build dependencies for kernel package"
yum-builddep kernel-$DISTROVERSION.src.rpm || die

echo "Unpacking kernel source"
rpmdev-setuptree >> $LOGFILE 2>&1 || die
rpm -Uvh kernel-$DISTROVERSION.src.rpm >> $LOGFILE 2>&1 || die
cd ~/rpmbuild/SPECS || die
rpmbuild -bp --target=$(uname -m) kernel.spec >> $LOGFILE 2>&1 || die
cd ~/rpmbuild/BUILD/kernel-* || die
cd linux-$ARCHVERSION || die
BUILD=$PWD
echo $LOCALVERSION > localversion

echo "Building the base kernel"
make -j$CPUS vmlinux >> $LOGFILE 2>&1 || die
TEMPDIR=`mktemp -d` || die
cp -R $KPATCHPATH/* $TEMPDIR || die
cp vmlinux $TEMPDIR || die

echo "Building the patched kernel"
patch -p1 < $PATCHFILE >> $LOGFILE 2>&1
make -j$CPUS vmlinux > $TEMPDIR/patched_build.log 2>&1 || die

echo "Detecting changed objects"
grep CC $TEMPDIR/patched_build.log | grep -v init/version.o | awk '{print $2}' >> $TEMPDIR/changed_objs
if [ $? -ne 0 ]
then
	echo "No changed objects"
	exit 0
fi

echo "Rebuilding changed objects"
mkdir $TEMPDIR/patched
for i in $(cat $TEMPDIR/changed_objs)
do
	rm -f $i
	KCFLAGS="-ffunction-sections -fdata-sections" make $i >> $LOGFILE 2>&1 || die
	strip -d $i
	cp -f $i $TEMPDIR/patched/
	
done
patch -R -p1 < $PATCHFILE >> $LOGFILE 2>&1
mkdir $TEMPDIR/base
for i in $(cat $TEMPDIR/changed_objs)
do
	rm -f $i
	KCFLAGS="-ffunction-sections -fdata-sections" make $i >> $LOGFILE 2>&1 || die
	strip -d $i
	cp -f $i $TEMPDIR/base/
done

echo "Extracting new and modified ELF sections"
cd $TEMPDIR
mkdir output
for i in base/* 
do
	FILE=`basename $i`
	./tools/create-diff-object base/$FILE patched/$FILE output/$FILE >> $LOGFILE 2>&1
done

echo "Building hotfix module"
ld -r -o output.o output/* >> $LOGFILE 2>&1 || die
./tools/add-patches-section output.o vmlinux >> $LOGFILE 2>&1 || die
KPATCH_BUILD=$BUILD make >> $LOGFILE 2>&1 || die
strip -d kpatch-patch.ko >> $LOGFILE 2>&1 || die
./tools/link-vmlinux-syms kpatch-patch.ko vmlinux >> $LOGFILE 2>&1 || die

echo "Patch generation complete"
cp -f $TEMPDIR/kpatch-patch.ko $BASE
echo "Cleaning up"
cleanup
echo "Done"