#!/bin/ksh
#
#  check_sym -- compare the symbols and external function references in two
#	versions of a shared library
#
#  SYNOPSIS
#	check_sym [-ch] [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.
#
#	check_sym uses fixed names in /tmp for its intermediate files,
#	as they contain useful details for those trying to understand
#	what changed.  If any of them cannot be created by the user,
#	the command will fail.  The files can be cleaned up using
#	the -c option.
#
#
#	The *basic* rules of thumb for library versions are: if you
#	 * stop exporting a symbol, or
#	 * change the size of a data symbol (not reported by check_sym)
#	 * 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
#	Should report changes in the size of exported data objects.
#

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 != "" ]]
}

cpu=$(uname -p)
if [[ $cpu = mips64* ]]
then
	file_list=/tmp/{D{,S,W,Y},J,S,U,d,j,r,s}{1,2}
else
	file_list=/tmp/{D{,S,W},J,S,U,d,j,r,s}{1,2}
fi

if [[ $1 = "-h" ]]
then
	echo "usage: $0 [-ch] [old [new]]"
	exit 0
elif [[ $1 = "-c" ]]
then
	rm -f $file_list
	exit 0
fi

# 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
	if [[ ! -f $1 ]]
	then
		echo "$1 doesn't exist" >&2
		exit 1
	fi
	new=$1
	shift
else
	# Dig info out of the just built library
	. ./shlib_version
	new=obj/${lib}.so.${major}.${minor}
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/\[<other>: [0-9a-f]*\]//'
}

# precreate all the files we'll use, but with noclobber set to avoid
# symlink attacks
set -C
files=
trap 'rm -f $files' 1 2 15 ERR
for i in $file_list
do
	rm -f $i
	3>$i
	files="$files $i"
done
set +C

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

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


if [[ $cpu = mips64* ]]
then
	readelf -d $old >/tmp/DY1
	readelf -d $new >/tmp/DY2
else
	rm -f /tmp/DY[12]
fi

jump_slots() { 
	case $cpu in
	hppa*)	awk '/IPLT/ && $5 != ""{print $5}' /tmp/r$1
		;;
	mips*)	gotsym=$(awk '$2 ~ /MIPS_GOTSYM/{print $3}' /tmp/DY$1)
		# the $(($foo)) is to convert hex to decimal
		awk -v g=$(($gotsym)) \
			'/^Symbol table ..symtab/{exit}
			$1+0 >= g && $4 == "FUNC" {print $8}' /tmp/s$1
		;;
	*)	awk '/JU*MP_SL/ && $5 != ""{print $5}' /tmp/r$1
		;;
	esac | sort -o /tmp/j$1
}

dynamic_sym() {
	# truncate the output files, to guarantee they exist
	>/tmp/U$1 >/tmp/DS$1 >/tmp/DW$1 >/tmp/D$1
	awk -v s=$1 '/^Symbol table ..symtab/{exit}
		! /^ *[1-9]/   {next}
		$7 == "UND"    {print $8 | ("sort -o /tmp/U" s); next }
		$5 == "GLOBAL" {print $8 | ("sort -o /tmp/DS" s) }
		$5 == "WEAK"   {print $8 | ("sort -o /tmp/DW" s) }
		$5 != "LOCAL"  {print $8 | ("sort -o /tmp/D" s) }
		{print $4, $5, $6, $8}' /tmp/s$1 | sort -o /tmp/d$1
#	awk -v s=$1 '$2 == "GLOBAL" {print $4 | ("sort -o /tmp/DS" s) }
#		     $2 == "WEAK"   {print $4 | ("sort -o /tmp/DW" s) }
#		     $1 != "SECTION"{print $4}' /tmp/d$1 | sort -o /tmp/D$1
}

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

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 $i
	comm -23 /tmp/j$i /tmp/U$i >/tmp/J$i
done

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

if false; then
	printf "\nReloc counts:\nbefore:\n" 
	grep ^R /tmp/r1
	printf "\nafter:\n"
	grep ^R /tmp/r2
fi

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