diff --git a/.gitignore b/.gitignore
index 1f36a17..fe7ac00 100644
--- a/.gitignore
+++ b/.gitignore
@@ -45,6 +45,7 @@
 
 # Generated folders
 /build
+/build.abi-check
 /Debug
 /Release
 /*/Debug
diff --git a/abi-check.sh b/abi-check.sh
index c3a88d0..a2a24a0 100755
--- a/abi-check.sh
+++ b/abi-check.sh
@@ -1,28 +1,164 @@
-#!/bin/sh
+#!/bin/bash
 
-set -e
+set -e -o pipefail
 
+RUNDIR=$(dirname "$0")
+RUNDIR=$(realpath "${RUNDIR}")
+
+. "${RUNDIR}/reltools/reltools.subr"
 # The 0.17 release is broken
-prev=0.18
-release=0.19
+#prev=0.18
+#release=0.19
 
-# ... clone json-c, abi-compliance-checker, abi-dumper
+prev=$(get_most_recent_relver)
+prevtag=$(get_most_recent_reltag "${prev}")
+release=$(get_ver_descr)
 
-if [ "$1" != "--skip-build" ] ; then
-	mkdir build
-	cd build
-	CFLAGS=-Og cmake -DCMAKE_INSTALL_PREFIX=~/json-c-installs/json-c-${release} ..
-	make && make test && make install
+ACCDIR=${RUNDIR}/../abi-compliance-checker
+ACC=${ACCDIR}/abi-compliance-checker.pl
+REPORTDIR=${ACCDIR}
+INSTBASE=${HOME}/json-c-installs
+
+usage()
+{
+	local exitval="$1" ; shift
+	local errmsg="$1"
+	if [ $exitval -ne 0 ] ; then
+		exec 1>&2
+	fi
+	if [ -n "$errmsg" ] ; then
+		echo "ERROR: $errmsg" 1>&2
+	fi
+	cat <<EOF
+Usage: $0 [--help] [--rebuild-old] [--rebuild-new] [--regen]
+          [--buildold] [--prev <tag>]
+          [-R <reportdir>] [-I <instdir>]
+  Build two versions of json-c and compare them with abi-compliance-checker
+
+  --rebuild-old - Re-build the previous version
+  --rebuild-new - Re-build the current version
+  --regen       - Always re-generate the ABI dumps
+  --buildold - Build the previous version if not yet done
+               By default, an old build must already exist.
+  --prev     - Specify an alternate old tag to compare against
+  --clean    - Rebuild and regen everything
+  -R         - Where to place output reports (${REPORTDIR})
+  -I         - Where to install json-c builds to (${INSTBASE})
+
+  Previous release: ${prev} (${prevtag})
+  Current version:  ${release}
+EOF
+	exit "$exitval"
+}
+
+REBUILD_NEW=0
+REBUILD_OLD=0
+BUILD_OLD=0
+REGEN_ABI_DUMPS=0
+
+while [ $# -gt 0 ] ; do
+	case "$1" in
+	--clean)
+		BUILD_OLD=1
+		REGEN_ABI_DUMPS=1
+		REBUILD_NEW=1
+		REBUILD_OLD=1
+		;;
+	--rebuild-new)
+		REBUILD_NEW=1
+		;;
+	--rebuild-old)
+		REBUILD_OLD=1
+		;;
+	--regen)
+		REGEN_ABI_DUMPS=1
+		;;
+	--buildold)
+		BUILD_OLD=1
+		;;
+	--prev)
+		prev="$2"
+		prevtag=$(get_most_recent_reltag "${prev}")
+		shift
+		;;
+	-R)
+		REPORTDIR="$2"
+		shift
+		;;
+	-I)
+		INSTBASE="$2"
+		shift
+		;;
+	-h|--help)
+		usage 0
+		;;
+	*)
+		usage 1 "Unknown args: $*"
+		;;
+	esac
+	shift
+done
+
+if [ ! -d "${ACCDIR}" ]; then
+	echo "Cloning abi-compliance-checker into ${ACCDIR}"
+	git clone https://github.com/lvc/abi-compliance-checker "${ACCDIR}"
 fi
 
-# Assume the old version has already been built
+if ! type -P perl > /dev/null ; then
+	echo "perl install needed: apt-get install perl, yum install perl, etc..." 1>&2
+	exit 1
+fi
+
+# ===============================
+
+build_new()
+{
+	local BUILD_DEST=${INSTBASE}/json-c-${release}
+	if [ ! -d "${BUILD_DEST}" ] || [ "${REBUILD_NEW}" -eq 1 ] ; then
+		echo "Building $(pwd) (${release}) into ${BUILD_DEST}"
+		rm -rf build.abi-check
+		mkdir -p build.abi-check/${release}
+		(
+			cd build.abi-check/${release}
+			CFLAGS=-Og cmake -DCMAKE_INSTALL_PREFIX="${BUILD_DEST}" ../..
+			make && make test
+			rm -rf "${BUILD_DEST}"
+			make install
+		)
+	fi
+}
+
+build_old()
+{
+	local BUILD_DEST=${INSTBASE}/json-c-${prev}
+	if [ ! -d "${BUILD_DEST}" ] && [ "${BUILD_OLD}" -eq 0 ] ; then
+		echo "ERROR: ${INSTBASE}/json-c-${prev} does not exist, pass --buildold to build it." 1>&2
+		exit 1
+	fi
+	if [ ! -d "${BUILD_DEST}" ] || [ "${REBUILD_OLD}" -eq 1 ] ; then
+		rm -rf "build.abi-check/${prev}"
+		git clone "${RUNDIR}" "build.abi-check/${prev}"
+		(
+			cd "build.abi-check/${prev}"
+			git -c advice.detachedHead=false checkout "${prevtag}"
+			echo "Building $(pwd) (${prevtag}) into ${BUILD_DEST}"
+			mkdir build.abi-check
+			cd build.abi-check
+			CFLAGS=-Og cmake -DCMAKE_INSTALL_PREFIX="${BUILD_DEST}" ..
+			make && make test
+			rm -rf "${BUILD_DEST}"
+			make install
+		)
+	fi
+}
 
-cd ~/abi-compliance-checker
 mkxml()
 {
+	local INSTREL
+	INSTREL=$(realpath --relative-to="${REPORTDIR}" "${INSTBASE}")
 	ver="$1"
-	if [ ! -e ../json-c-installs/json-c-${ver}/lib64 ] ; then
-		ln -s lib ../json-c-installs/json-c-${ver}/lib64
+	if [ ! -e "${INSTBASE}/json-c-${ver}/lib64" ] ; then
+		ln -s lib "${INSTBASE}/json-c-${ver}/lib64"
 	fi
 cat <<EOF > json-c-${ver}.xml
 <foo>
@@ -31,20 +167,48 @@ cat <<EOF > json-c-${ver}.xml
 </version>
 
 <headers>
-../json-c-installs/json-c-${ver}/include/json-c
+${INSTREL}/json-c-${ver}/include/json-c
 </headers>
 
 <libs>
-../json-c-installs/json-c-${ver}/lib64/libjson-c.so
+${INSTREL}/json-c-${ver}/lib64/libjson-c.so
 </libs>
 </foo>
 EOF
 }
+
+abidump()
+{
+	local libver="$1" ; shift
+
+	local dumppath="./ABI-${libver}.dump"
+	if [ "${REGEN_ABI_DUMPS}" -eq 1 ] ; then
+		rm -f "${dumppath}"
+	fi
+	if [ ! -e "${dumppath}" ] ; then
+		perl "${ACC}" -lib json-c -dump json-c-${libver}.xml -dump-path "${dumppath}"
+	else
+		echo "ABI dump already exists at ${dumppath}"
+	fi
+}
+
+# ===============================
+
+mkdir -p "${REPORTDIR}"
+
+build_old
+build_new
+
+cd "${REPORTDIR}"
 mkxml ${release}
 mkxml ${prev}
 
-perl abi-compliance-checker.pl -lib json-c -dump json-c-${prev}.xml -dump-path ./ABI-${prev}.dump
-perl abi-compliance-checker.pl -lib json-c -dump json-c-${release}.xml -dump-path ./ABI-${release}.dump
-perl abi-compliance-checker.pl -l json-c -old ABI-${prev}.dump -new ABI-${release}.dump
+echo "=== Generating ABI dumps ==="
+abidump ${prev}
+abidump ${release}
 
-echo "look in compat_reports/json-c/..."
+echo "=== Comparing ABIs ==="
+perl "${ACC}" -l json-c -old ABI-${prev}.dump -new ABI-${release}.dump
+
+echo
+echo "Look in $(pwd)/compat_reports/json-c/${prev}_to_${release}"
diff --git a/reltools/reltools.subr b/reltools/reltools.subr
index 51b7432..f78684f 100644
--- a/reltools/reltools.subr
+++ b/reltools/reltools.subr
@@ -5,8 +5,9 @@ JSON_C_TOP=${rt_RUNDIR}/..
 
 get_most_recent_reltag()
 {
+	local PATTERN="json-c-${1}*"
 	local RELTAG
-	RELTAG=$(git tag | tail -1)
+	RELTAG=$(git tag --list "${PATTERN}" | tail -1)
 	echo "${RELTAG}"
 }
 get_most_recent_relver()