scripts/trylink

#!/bin/sh

debug=false

try() {
    printf "%s\n" "Output of:" >$EXE.out
    printf "%s\n" "$*" >>$EXE.out
    printf "%s\n" "==========" >>$EXE.out
    $debug && echo "Trying: $*"
    "$@" >>$EXE.out 2>&1
    exitcode=$?
    cat $EXE.out
    return $exitcode
}

EXE="$1"
CC="$2"
LDFLAGS="$3"
O_FILES="$4"
A_FILES="$5"
LDLIBS="$6"

# Sanitize lib list (dups, extra spaces etc)
LDLIBS=`echo "$LDLIBS" | xargs -n1 | sort | uniq | xargs`

# First link with all libs. If it fails, bail out
echo "Trying libraries: $LDLIBS"
# "lib1 lib2 lib3" -> "-llib1 -llib2 -llib3"
l_list=`echo "$LDLIBS" | sed -e 's/ / -l/g' -e 's/^/-l/' -e 's/^-l$//'`
test "x$l_list" != "x" && l_list="-Wl,--start-group $l_list -Wl,--end-group"
try $CC $LDFLAGS \
	-o $EXE -Wl,-Map -Wl,$EXE.map \
	-Wl,--warn-common -Wl,--sort-common -Wl,--gc-sections \
	-Wl,--start-group $O_FILES $A_FILES -Wl,--end-group \
	$l_list \
	>/dev/null \
|| {
    echo "Failed: $* $l_list"
    cat $EXE.out
    exit 1
}

# Now try to remove each lib and build without it.
# Stop when no lib can be removed.
while test "$LDLIBS"; do
    $debug && echo "Trying libraries: $LDLIBS"
    all_needed=true
    for one in $LDLIBS; do
	without_one=`echo " $LDLIBS " | sed "s/ $one / /g" | xargs`
	# "lib1 lib2 lib3" -> "-llib1 -llib2 -llib3"
	l_list=`echo "$without_one" | sed -e 's/ / -l/g' -e 's/^/-l/' -e 's/^-l$//'`
	test "x$l_list" != "x" && l_list="-Wl,--start-group $l_list -Wl,--end-group"
	$debug && echo "Trying -l options: '$l_list'"
	try $CC $LDFLAGS \
		-o $EXE -Wl,-Map -Wl,$EXE.map \
		-Wl,--warn-common -Wl,--sort-common -Wl,--gc-sections \
		-Wl,--start-group $O_FILES $A_FILES -Wl,--end-group \
		$l_list \
		>/dev/null
	if test $? = 0; then
	    echo "Library $one is not needed"
	    LDLIBS="$without_one"
	    all_needed=false
	else
	    echo "Library $one is needed"
	fi
    done
    # All libs were needed, can't remove any
    $all_needed && break
    # If there is no space char, the list has just one lib.
    # I'm not sure that in this case lib really is 100% needed.
    # Let's try linking without it anyway... thus commented out.
    #{ echo "$LDLIBS" | grep -q ' '; } || break
done

# Make the binary with final, minimal list of libs
echo "Final link with: $LDLIBS"
l_list=`echo "$LDLIBS" | sed -e 's/ / -l/g' -e 's/^/-l/' -e 's/^-l$//'`
test "x$l_list" != "x" && l_list="-Wl,--start-group $l_list -Wl,--end-group -Wl,--verbose"
# --verbose gives us gobs of info to stdout (e.g. linker script used)
if ! test -f busybox_ldscript; then
    try $CC $LDFLAGS \
	    -o $EXE -Wl,-Map -Wl,$EXE.map \
	    -Wl,--warn-common -Wl,--sort-common -Wl,--gc-sections \
	    -Wl,--start-group $O_FILES $A_FILES -Wl,--end-group \
	    $l_list -Wl,--verbose \
	    >/dev/null
else
    echo "Custom linker script 'busybox_ldscript' found, using it"
    # Add SORT_BY_ALIGNMENT to linker script (found in $EXE.out):
    #  .rodata         : { *(.rodata SORT_BY_ALIGNMENT(.rodata.*) .gnu.linkonce.r.*) }
    #  *(.data SORT_BY_ALIGNMENT(.data.*) .gnu.linkonce.d.*)
    #  *(.bss SORT_BY_ALIGNMENT(.bss.*) .gnu.linkonce.b.*)
    # This will eliminate most of the padding (~3kb).
    try $CC $LDFLAGS \
	    -o $EXE -Wl,-Map -Wl,$EXE.map \
	    -Wl,--warn-common -Wl,--sort-common -Wl,--gc-sections \
	    -Wl,--start-group $O_FILES $A_FILES -Wl,--end-group \
	    $l_list -Wl,--verbose \
	    -Wl,-T -Wl,busybox_ldscript \
	    >/dev/null
fi

mkdir 0lib 2>/dev/null
test -d 0lib || exit 1
ln -s libbusybox.so.1.8.0 0lib/libbusybox.so 2>/dev/null

EXE="0lib/libbusybox.so.1.8.0"
try $CC $LDFLAGS \
	-o $EXE -Wl,-Map -Wl,$EXE.map \
	-shared -fPIC -Wl,--enable-new-dtags \
	-Wl,--start-group -Wl,--whole-archive $A_FILES -Wl,--no-whole-archive -Wl,--end-group \
	$l_list -Wl,--verbose \
	-Wl,-soname="libbusybox.so.1.8.0" \
	-Wl,-z,combreloc \
	>/dev/null \
|| {
    echo "Linking $EXE failed"
    exit 1
}
strip -s --remove-section=.note --remove-section=.comment $EXE

EXE="0lib/busybox"
try $CC $LDFLAGS \
	-o $EXE -Wl,-Map -Wl,$EXE.map \
	-Wl,--warn-common -Wl,--sort-common -Wl,--gc-sections \
	-Wl,--start-group $O_FILES -Wl,--end-group \
	$l_list -Wl,--verbose \
	-L"0lib" -lbusybox \
	>/dev/null \
|| {
    echo "Linking $EXE failed"
    exit 1
}
strip -s --remove-section=.note --remove-section=.comment $EXE