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By default, put intermediate files in a temp dir and remove it on
completion.  To leave files in /tmp, use new -k option.

#!/bin/ksh
#  $OpenBSD: check_sym,v 1.11 2022/01/03 03:40:48 guenther Exp $
#
# Copyright (c) 2016,2019,2022 Philip Guenther <guenther@openbsd.org>
#
# Permission to use, copy, modify, and distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
#
#
#  check_sym -- compare the symbols and external function references in two
#	versions of a shared library
#
#  SYNOPSIS
#	check_sym [-chkv] [old [new]]
#
#  DESCRIPTION
#	Library developers need to be aware when they have changed the
#	ABI of a library.  To assist them, check_sym examines two versions
#	of a shared library and reports changes to the following:
#	 * the set of exported symbols and their strengths
#	 * the set of undefined symbols referenced
#	 * the set of lazily-resolved functions (PLT)
#
#	In each case, additions and removals are reported; for exported
#	symbols it also reports when a symbol is weakened or strengthened.
#
#	The shared libraries to compare can be specified on the
#	command-line.  Otherwise, check_sym expects to be run from the
#	source directory of a library with a shlib_version file specifying
#	the version being built and the new library in the obj subdirectory.
#	If the old library to compare against wasn't specified either then
#	check_sym will take the highest version of that library in the
#	*current* directory, or the highest version of that library in
#	/usr/lib if it wasn't present in the current directory.
#
#	By default, check_sym places all its intermediate files in a
#	temporary directory and removed it on exit.  They contain useful
#	details for understanding what changed, so if the -k option is used
#	they will instead be placed in /tmp/ and left behind.  If any of
#	them cannot be created by the user, the command will fail.  The
#	files left behind by the -k option can be cleaned up by invoking
#	check_syms with the -c option.
#
#	The -v option enables verbose output.
#
#	The *basic* rules of thumb for library versions are: if you
#	 * stop exporting a symbol, or
#	 * change the size of a data symbol
#	 * start exporting a symbol that an inter-dependent library needs
#	then you need to bump the MAJOR version of the library.
#
#	Otherwise, if you:
#	 * start exporting a symbol
#	then you need to bump the MINOR version of the library.
#
#  SEE ALSO
#	readelf(1), elf(5)
#
#  AUTHORS
#	Philip Guenther <guenther@openbsd.org>
#
#  CAVEATS
#	The elf format is infinitely extendable, but check_sym only
#	handles a few weirdnesses.  Running it on or against new archs
#	may result in meaningless results.
#
#  BUGS
#	While the author stills find the intermediate files useful,
#	most people won't.  By default they should be placed in a
#	temp directory and removed.
#

get_lib_name()
{
	sed -n 's/^[ 	]*LIB[ 	]*=[ 	]*\([^ 	]*\).*/\1/p' "$@"
}

pick_highest()
{
	old=
	omaj=-1
	omin=0
	for i
	do
		[[ -f $i ]] || continue
		maj=${i%.*}; maj=${maj##*.}
		min=${i##*.}
		if [[ $maj -gt $omaj || ( $maj -eq $omaj && $min -gt $omin ) ]]
		then
			old=$i
			omaj=$maj
			omin=$min
		fi
	done
	[[ $old != "" ]]
}

usage()
{
	usage="usage: check_sym [-chkv] [old [new]]"
	if [[ $# -gt 0 ]]
	then
		echo "check_sym: $@
$usage" >&2
		exit 1
	fi
	echo "$usage"
	exit 0
}

unset odir
file_list={D{,S,W,O},J,S,U,d,j,r,s}{1,2}

keep_temp=false
verbose=false
while getopts :chkv opt "$@"
do
	case $opt in
	c)	rm -f /tmp/$file_list
		exit 0;;
	h)	usage;;
	k)	keep_temp=true;;
	v)	verbose=true;;
	\?)	usage "unknown option -- $OPTARG";;
	esac
done
shift $((OPTIND - 1))
[[ $# -gt 2 ]] && usage "too many arguments"

# Old library?
if [[ $1 = ?(*/)lib*.so* ]]
then
	if [[ ! -f $1 ]]
	then
		echo "$1 doesn't exist" >&2
		exit 1
	fi
	old=$1
	lib=${old##*/}
	lib=${lib%%.so.*}
	shift
else
	# try determining it from the current directory
	if [[ -f Makefile ]] && lib=$(get_lib_name Makefile) &&
	   [[ $lib != "" ]]
	then
		lib=lib$lib
	else
		lib=libc
	fi

	# Is there a copy of that lib in the current directory?
	# If so, use the highest numbered one
	if ! pick_highest $lib.so.* && ! pick_highest /usr/lib/$lib.so.*
	then
		echo "unable to find $lib.so.*" >&2
		exit 1
	fi
fi

# New library?
if [[ $1 = ?(*/)lib*.so* ]]
then
	new=$1
	shift
else
	# Dig info out of the just built library
	. ./shlib_version
	new=obj/${lib}.so.${major}.${minor}
fi
if [[ ! -f $new ]]
then
	echo "$new doesn't exist" >&2
	exit 1
fi

# Filter the output of readelf -s to be easier to parse by removing a
# field that only appears on some symbols: [<other>: 88]
# Not really arch-specific, but I've only seen it on alpha
filt_symtab() {
	sed 's/\[<other>: [0-9a-f]*\]//'
}

if $keep_temp
then
	# precreate all the files we'll use, but with noclobber set to avoid
	# symlink attacks
	odir=/tmp
	files=
	trap 'ret=$?; rm -f $files; exit $ret' 1 2 15 ERR
else
	trap 'ret=$?; rm -rf "$odir"; exit $ret' 0 1 2 15 ERR
	odir=$(mktemp -dt check_sym.XXXXXXXXXX)
fi
set -C
for i in $odir/$file_list
do
	rm -f $i
	3>$i
	files="$files $i"
done
set +C

readelf -rW $old > $odir/r1
readelf -rW $new > $odir/r2

readelf -sW $old | filt_symtab > $odir/s1
readelf -sW $new | filt_symtab > $odir/s2


case $(readelf -h $new | grep '^ *Machine:') in
*MIPS*)	cpu=mips64;;
*HPPA*)	cpu=hppa;;
*)	cpu=dontcare;;
esac

if [[ $cpu = mips64 ]]
then
	gotsym1=$(readelf -d $old | awk '$2 ~ /MIPS_GOTSYM/{print $3}')
	gotsym2=$(readelf -d $new | awk '$2 ~ /MIPS_GOTSYM/{print $3}')
fi

# Now that we're done accessing $old and $new (which could be
# relative paths), chdir into our work directory, whatever it is
cd $odir

jump_slots() { 
	case $cpu in
	hppa)	awk '/IPLT/ && $5 != ""{print $5}' r$1
		;;
	mips64)	# the $((gotsym$1)) converts hex to decimal
		awk -v g=$((gotsym$1)) \
			'/^Symbol table ..symtab/{exit}
			$6 == "PROTECTED" { next }
			$1+0 >= g && $4 == "FUNC" {print $8}' s$1
		;;
	*)	awk '/JU*MP_SL/ && $5 != ""{print $5}' r$1
		;;
	esac | sort -o j$1
}

dynamic_sym() {
	awk -v s=$1 '/^Symbol table ..symtab/{exit}
		! /^ *[1-9]/   {next}
		$7 == "UND"    {print $8 | ("sort -o U" s); next }
		$5 == "GLOBAL" {print $8 | ("sort -o DS" s) }
		$5 == "WEAK"   {print $8 | ("sort -o DW" s) }
		$5 != "LOCAL"  {print $8 | ("sort -o D" s) }
		$5 != "LOCAL" && $4 == "OBJECT" {
				print $8, $3 | ("sort -o DO" s) }
		{print $4, $5, $6, $8}' s$1 | sort -o d$1
}

static_sym() { 
	awk '/^Symbol table ..symtab/{s=1}
	     /LOCAL/{next}
	     s&&/^ *[1-9]/{print $4, $5, $6, $8}' s$1 | sort -o S$1
}

data_sym_changes() {
	join "$@" | awk '$2 != $3 { print $1 " " $2 " --> " $3 }'
}

output_if_not_empty() {
	leader=$1
	shift
	if "$@" | grep -q .
	then
		echo "$leader"
		"$@" | sed 's:^:	:'
		echo
	fi
}


for i in 1 2
do
	jump_slots $i
	dynamic_sym $i
	static_sym $i
	comm -23 j$i U$i >J$i
done

echo "$old --> $new"
if cmp -s d[12] && cmp -s DO[12]
then
	printf "No dynamic export changes\n"
else
	printf "Dynamic export changes:\n"
	output_if_not_empty "added:" comm -13 D[12]
	output_if_not_empty "removed:" comm -23 D[12]
	output_if_not_empty "weakened:" comm -12 DS1 DW2
	output_if_not_empty "strengthened:" comm -12 DW1 DS2
	output_if_not_empty "data object sizes changes:" \
					data_sym_changes DO[12]
fi
if ! cmp -s U[12]
then
	printf "External reference changes:\n"
	output_if_not_empty "added:" comm -13 U[12]
	output_if_not_empty "removed:" comm -23 U[12]
fi

if $verbose; then
	printf "\nReloc counts:\nbefore:\n" 
	grep ^R r1
	printf "\nafter:\n"
	grep ^R r2
fi

output_if_not_empty "PLT added:" comm -13 J1 J2
output_if_not_empty "PLT removed:" comm -23 J1 J2