#!/bin/bash

# kpatch build script

# 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 currently only works on Fedora and will need to be adapted to
# work on other distros.

# This script:
# - Downloads the kernel src rpm for the currently running kernel
# - 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="$PWD"
LOGFILE="/tmp/kpatch-build-$(date +%s).log"
TOOLSDIR="$(readlink -f $(dirname $0))"
ARCHVERSION="$(uname -r)"
DISTROVERSION="${ARCHVERSION%*.*}"
CPUS="$(grep -c ^processor /proc/cpuinfo)"
LOCALVERSION="$(uname -r)"
LOCALVERSION="-${LOCALVERSION##*-}"
KSRCDIR="$HOME/.kpatch/$ARCHVERSION"
KSRCDIR_DIR="$(dirname $KSRCDIR)"
TEMPDIR=
STRIPCMD="strip -d --keep-file-symbols"
APPLIEDPATCHFILE="applied-patch"

die() {
	if [[ -z $1 ]]; then
		echo "ERROR: kpatch build failed. Check $LOGFILE for more details." >&2
	else
		echo "ERROR: $1" >&2
	fi
	exit 1
}

find_data_dir() {
	# git repo
	DATADIR="$(readlink -f $TOOLSDIR/../kmod)"
	[[ -e "$DATADIR" ]] && return

	# installation path
	DATADIR="$(readlink -f $TOOLSDIR/../../share/kpatch)"
	[[ -e "$DATADIR" ]] && return

	return 1
}

if [[ "$#" -ne 1 ]]; then
	echo "usage: $0 patchfile" >&2
	exit 2
fi

PATCHFILE="$(readlink -f $1)"
if [[ ! -f "$PATCHFILE" ]]; then
	echo "ERROR: patch file $PATCHFILE not found" >&2
	exit 3
fi

PATCHNAME="$(basename $PATCHFILE)"
if [[ "$PATCHNAME" =~ \.patch ]] || [[ "$PATCHNAME" =~ \.diff ]]; then
	PATCHNAME="${PATCHNAME%.*}"
fi

TEMPDIR="$(mktemp -d)" || die "mktemp failed"

trap "rm -rf $TEMPDIR" EXIT INT TERM

if [[ -d "$KSRCDIR" ]]; then
	echo "Using cache at $KSRCDIR"
	cd "$KSRCDIR" || die
	if [[ -f "$APPLIEDPATCHFILE" ]]; then
		patch -R -p1 < "$APPLIEDPATCHFILE" || die "the kpatch cache is corrupted. \"rm -rf $KSRCDIR\" and try again"
		rm -f "$APPLIEDPATCHFILE"
	fi
	make "-j$CPUS" vmlinux >> "$LOGFILE" 2>&1 || die
else
	rpm -q --quiet rpmdevtools || die "rpmdevtools not installed"
	rpm -q --quiet yum-utils || die "yum-utils not installed"

	echo "Downloading kernel source for $ARCHVERSION"
	yumdownloader --source --destdir "$TEMPDIR" "kernel-$ARCHVERSION" >> "$LOGFILE" 2>&1 || die

	echo "Unpacking kernel source"
	rpmdev-setuptree >> "$LOGFILE" 2>&1 || die
	rpm -ivh "$TEMPDIR/kernel-$DISTROVERSION.src.rpm" >> "$LOGFILE" 2>&1 || die
	rpmbuild -bp "--target=$(uname -m)" "$HOME/rpmbuild/SPECS/kernel.spec" >> "$LOGFILE" 2>&1 ||
		die "rpmbuild -bp failed.  you may need to run 'yum-builddep kernel' first."
	mkdir -p "$KSRCDIR_DIR"
	mv "$HOME"/rpmbuild/BUILD/kernel-*/linux-"$ARCHVERSION" "$KSRCDIR" >> "$LOGFILE" 2>&1 || die

	echo "Building original kernel"
	cd "$KSRCDIR"
	echo "$LOCALVERSION" > localversion || die
	make "-j$CPUS" vmlinux >> "$LOGFILE" 2>&1 || die
fi

find_data_dir || (echo "can't find data dir" >&2 && die)

cp -LR "$DATADIR/patch" "$TEMPDIR" || die
cp vmlinux "$TEMPDIR" || die

echo "Building patched kernel"
cp "$PATCHFILE" "$APPLIEDPATCHFILE" || die
patch -p1 < "$APPLIEDPATCHFILE" >> "$LOGFILE" 2>&1 || die
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 1
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
	$STRIPCMD "$i" >> "$LOGFILE" 2>&1 || die
	mkdir -p "$TEMPDIR/patched/$(dirname $i)"
	cp -f "$i" "$TEMPDIR/patched/$i" || die
	
done
patch -R -p1 < "$APPLIEDPATCHFILE" >> "$LOGFILE" 2>&1
rm -f "$APPLIEDPATCHFILE"
mkdir "$TEMPDIR/orig"
for i in $(cat $TEMPDIR/changed_objs); do
	rm -f "$i"
	KCFLAGS="-ffunction-sections -fdata-sections" make "$i" >> "$LOGFILE" 2>&1 || die
	$STRIPCMD -d "$i" >> "$LOGFILE" 2>&1 || die
	mkdir -p "$TEMPDIR/orig/$(dirname $i)"
	cp -f "$i" "$TEMPDIR/orig/$i" || die
done

echo "Extracting new and modified ELF sections"
cd "$TEMPDIR/orig"
FILES="$(find * -type f)"
cd "$TEMPDIR"
mkdir output
for i in $FILES; do
	mkdir -p "output/$(dirname $i)"
	"$TOOLSDIR"/create-diff-object "orig/$i" "patched/$i" "output/$i" >> "$LOGFILE" 2>&1 || die
done

echo "Building patch module: kpatch-$PATCHNAME.ko"
cd "$TEMPDIR/output"
ld -r -o ../patch/output.o $FILES >> "$LOGFILE" 2>&1 || die
cd "$TEMPDIR/patch"
"$TOOLSDIR"/add-patches-section output.o ../vmlinux >> "$LOGFILE" 2>&1 || die
KPATCH_BUILD="$KSRCDIR" KPATCH_NAME="$PATCHNAME" make >> "$LOGFILE" 2>&1 || die
$STRIPCMD "kpatch-$PATCHNAME.ko" >> "$LOGFILE" 2>&1 || die
"$TOOLSDIR"/link-vmlinux-syms "kpatch-$PATCHNAME.ko" ../vmlinux >> "$LOGFILE" 2>&1 || die

cp -f "$TEMPDIR/patch/kpatch-$PATCHNAME.ko" "$BASE" || die

rm -f "$LOGFILE"

echo "SUCCESS"