kpatch: support eu-readelf as alternative to GNU readelf

The kpatch script is used to load live patches on production systems
that may be stripped down, with binutils (which provides readelf) not
installed while elfutils (which provides eu-readelf) is available. Add
a get_module_section_string() helper that auto-detects the available
tool at startup and uses the appropriate invocation for each.

Other readelf usages in the build tooling (kpatch-build, lookup.c,
test infrastructure) are left unchanged, as a compiler toolchain
including binutils can reasonably be expected in a build environment.

Signed-off-by: Stephen Cheng <stephen.cheng@citrix.com>

Author: Stephen Cheng

kpatch/kpatch

@@ -25,6 +25,15 @@
 
 INSTALLDIR=/var/lib/kpatch
 SCRIPTDIR="$(readlink -f "$(dirname "$(type -p "$0")")")"
+if command -v readelf >/dev/null 2>&1; then
+	get_module_section_string() {
+		readelf -p "$2" "$1" | grep '\[.*\]' | awk '{print $3}'
+	}
+else
+	get_module_section_string() {
+		eu-readelf --string-dump="$2" "$1" | awk 'NF>=3 && /^\s*\[/ {print $3; exit}'
+	}
+fi
 VERSION="0.9.11"
 POST_ENABLE_WAIT=15	# seconds
 POST_SIGNAL_WAIT=60	# seconds
@@ -135,7 +144,7 @@ core_loaded () {
 }
 
 get_module_name () {
-	readelf -p .gnu.linkonce.this_module "$1" | grep '\[.*\]' | awk '{print $3}'
+	get_module_section_string "$1" .gnu.linkonce.this_module
 }
 
 init_sysfs_var() {
@@ -159,7 +168,7 @@ verify_module_checksum () {
 	modname="$(get_module_name "$1")"
 	[[ -z "$modname" ]] && return 1
 
-	checksum="$(readelf -p .kpatch.checksum "$1" 2>&1 | grep '\[.*\]' | awk '{print $3}')"
+	checksum="$(get_module_section_string "$1" .kpatch.checksum 2>/dev/null)"
 
 	# Fail checksum match only if both exist and diverge
 	if [[ -n "$checksum" ]] && [[ -e "$SYSFS/${modname}/checksum" ]] ; then