build: rework library bundling

Rework the bundle-libraries.sh implementation to use a more robust approach
for executing host binaries through the shipped ELF loader and libraries.

The previous approach relied on symlinks pointing to a wrapper script which
caused various issues, especially with multicall binaries as the original
argv[0] name was not preserved through the ld.so invocation. Another down-
side was the fact that the actual binaries got moved into another directory
which caused executables to fail looking up resources with paths relative
to the executable location.

The new library wrapper implements the following improvements:

 - Instead of symlinks pointing to a common wrapper, each ELF executable
   is now replaced by a unqiue shell script which retains the original
   program name getting called

 - Instead of letting ld.so invoke the ELF executable directly, launch
   the final ELF binary through a helper program which fixes up the argv[0]
   argument for the target program

 - Support sharing a common location for the bundled libraries instead of
   having one copy in each directory containing wrapped binaries

Finally modify the SDK build to wrap the staging_dir and toolchain binaries
which allows to use the SDK on systems with a different glibc version.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

scripts/bundle-libraries.sh

@@ -2,7 +2,7 @@
 #
 #   Script to install host system binaries along with required libraries.
 #
-#   Copyright (C) 2012-2013 Jo-Philipp Wich <jo@mein.io>
+#   Copyright (C) 2012-2017 Jo-Philipp Wich <jo@mein.io>
 #
 #   This program is free software; you can redistribute it and/or modify
 #   it under the terms of the GNU General Public License as published by
@@ -27,6 +27,13 @@ _cp() {
 	}
 }
 
+_mv() {
+	mv ${VERBOSE:+-v} "$1" "$2" || {
+		echo "mv($1 $2) failed" >&2
+		exit 1
+	}
+}
+
 _md() {
 	mkdir ${VERBOSE:+-v} -p "$1" || {
 		echo "mkdir($1) failed" >&2
@@ -41,6 +48,52 @@ _ln() {
 	}
 }
 
+_relpath() {
+	local base="$(readlink -f "$1")"
+	local dest="$(readlink -f "$2")"
+	local up
+
+	[ -d "$base" ] || base="${base%/*}"
+	[ -d "$dest" ] || dest="${dest%/*}"
+
+	while true; do
+		case "$base"
+			in "$dest"/*)
+				echo "$up/${base#$dest/}"
+				break
+			;;
+			*)
+				dest="${dest%/*}"
+				up="${up:+$up/}.."
+			;;
+		esac
+	done
+}
+
+_wrapper() {
+	cat <<-EOT | ${CC:-gcc} -x c -o "$1" -
+		#include <unistd.h>
+		#include <stdio.h>
+
+		int main(int argc, char **argv) {
+			const char *self   = argv[0];
+			const char *target = argv[1];
+
+			if (argc < 3) {
+				fprintf(stderr, "Usage: %s executable arg0 [args...]\n", self);
+				return 1;
+			}
+
+			return execv(target, argv + 2);
+		}
+	EOT
+
+	[ -x "$1" ] || {
+		echo "compiling wrapper failed" >&2
+		exit 5
+	}
+}
+
 for LDD in ${PATH//://ldd }/ldd; do
 	"$LDD" --version >/dev/null 2>/dev/null && break
 	LDD=""
@@ -49,29 +102,31 @@ done
 [ -n "$LDD" -a -x "$LDD" ] || LDD=
 
 for BIN in "$@"; do
-	[ -n "$BIN" -a -x "$BIN" -a -n "$DIR" ] || {
+	[ -n "$BIN" -a -n "$DIR" ] || {
 		echo "Usage: $0 <destdir> <executable> ..." >&2
 		exit 1
 	}
 
-	[ ! -d "$DIR/bundled/lib" ] && {
+	[ ! -d "$DIR/lib" ] && {
-		_md "$DIR/bundled/lib"
+		_md "$DIR/lib"
-		_md "$DIR/bundled/usr"
+		_md "$DIR/usr"
-		_ln "../lib" "$DIR/bundled/usr/lib"
+		_ln "../lib" "$DIR/usr/lib"
+	}
+
+	[ ! -x "$DIR/lib/runas" ] && {
+		_wrapper "$DIR/lib/runas"
 	}
 
 	LDSO=""
 
-	echo "Bundling ${BIN##*/}"
+	[ -n "$LDD" ] && [ -x "$BIN" ] && file "$BIN" | grep -sqE "ELF.*executable" && {
-	[ -n "$LDD" ] && {
 		for token in $("$LDD" "$BIN" 2>/dev/null); do
 			case "$token" in */*.so*)
 				case "$token" in
 					*ld-*.so*) LDSO="${token##*/}" ;;
-					*) echo " * lib: ${token##*/}" ;;
 				esac
 
-				dest="$DIR/bundled/lib/${token##*/}"
+				dest="$DIR/lib/${token##*/}"
 				ddir="${dest%/*}"
 
 				[ -f "$token" -a ! -f "$dest" ] && {
@@ -82,29 +137,22 @@ for BIN in "$@"; do
 		done
 	}
 
-	_md "$DIR"
-
 	# is a dynamically linked executable
 	if [ -n "$LDSO" ]; then
-		_cp "$BIN" "$DIR/bundled/${BIN##*/}"
+		echo "Bundling ${BIN##*/}"
 
+		RUNDIR="$(readlink -f "$BIN")"; RUNDIR="${RUNDIR%/*}"
 		RUN="${LDSO#ld-}"; RUN="run-${RUN%%.so*}.sh"
+		REL="$(_relpath "$DIR/lib" "$BIN")"
 
-		[ -x "$DIR/bundled/$RUN" ] || {
+		_mv "$BIN" "$RUNDIR/.${BIN##*/}.bin"
-			cat <<-EOF > "$DIR/bundled/$RUN"
-				#!/usr/bin/env bash
-				dir="\$(dirname "\$0")"
-				bin="\$(basename "\$0")"
-				exec -a "\$0" "\$dir/bundled/lib/$LDSO" --library-path "\$dir/bundled/lib" "\$dir/bundled/\$bin" "\$@"
-			EOF
-			chmod ${VERBOSE:+-v} 0755 "$DIR/bundled/$RUN"
-		}
 
-		_ln "./bundled/$RUN" "$DIR/${BIN##*/}"
+		cat <<-EOF > "$BIN"
+			#!/usr/bin/env bash
+			dir="\$(dirname "\$0")"
+			exec "\$dir/${REL:+$REL/}$LDSO" --library-path "\$dir/${REL:+$REL/}" "\$dir/${REL:+$REL/}runas" "\$dir/.${BIN##*/}.bin" "\$0" "\$@"
+		EOF
 
-	# is a static executable or non-elf binary
+		chmod ${VERBOSE:+-v} 0755 "$BIN"
-	else
-		[ -n "$LDD" ] && echo " * not dynamically linked"
-		_cp "$BIN" "$DIR/${BIN##*/}"
 	fi
 done

target/imagebuilder/Makefile

@@ -66,16 +66,20 @@ endif
 		$(PKG_BUILD_DIR)/target/linux/*/patches{,-*}
 	-cp $(KERNEL_BUILD_DIR)/* $(IB_KDIR)/ # don't copy subdirectories here
 	-cp $(LINUX_DIR)/.config $(IB_LDIR)/
-	-$(SCRIPT_DIR)/bundle-libraries.sh $(IB_LDIR)/scripts/dtc \
+	if [ -x $(LINUX_DIR)/scripts/dtc/dtc ]; then \
-	  $(LINUX_DIR)/scripts/dtc/dtc
+		$(INSTALL_DIR) $(IB_LDIR)/scripts/dtc; \
+		$(INSTALL_BIN) $(LINUX_DIR)/scripts/dtc/dtc $(IB_LDIR)/scripts/dtc/dtc; \
+	fi
 	if [ -d $(LINUX_DIR)/arch/$(ARCH)/boot/dts ]; then \
 		$(CP) $(LINUX_DIR)/arch/$(ARCH)/boot/dts/* $(IB_DTSDIR); \
 	fi
 	$(SED) 's,^# REVISION:=.*,REVISION:=$(REVISION),g' $(PKG_BUILD_DIR)/include/version.mk
 	find $(PKG_BUILD_DIR) -name CVS -o -name .git -o -name .svn \
 	  | $(XARGS) rm -rf
-	find $(STAGING_DIR_HOST)/bin -maxdepth 1 -type f -perm -u=x \
+	$(INSTALL_DIR) $(PKG_BUILD_DIR)/staging_dir/host/bin
-	  | $(XARGS) $(SCRIPT_DIR)/bundle-libraries.sh $(PKG_BUILD_DIR)/staging_dir/host/bin/
+	$(CP) $(STAGING_DIR_HOST)/bin/* $(PKG_BUILD_DIR)/staging_dir/host/bin/
+	(cd $(PKG_BUILD_DIR); find staging_dir/host/bin/ $(IB_LDIR)/scripts/dtc/ -type f | \
+		$(XARGS) $(SCRIPT_DIR)/bundle-libraries.sh $(PKG_BUILD_DIR)/staging_dir/host)
 	STRIP=sstrip $(SCRIPT_DIR)/rstrip.sh $(PKG_BUILD_DIR)/staging_dir/host/bin/
 	$(TAR) -cf - -C $(BUILD_DIR) $(IB_NAME) | xz -zc -7e > $@
 

target/sdk/Makefile

@@ -76,6 +76,10 @@ $(BIN_DIR)/$(SDK_NAME).tar.xz: clean
 		$(SDK_DIRS) $(KERNEL_FILES) | \
 		$(TAR) -xf - -C $(SDK_BUILD_DIR)
 
+	(cd $(SDK_BUILD_DIR); find $(STAGING_SUBDIR_HOST)/bin $(STAGING_SUBDIR_HOST)/usr/bin \
+		$(STAGING_SUBDIR_TOOLCHAIN)/bin $(STAGING_SUBDIR_TOOLCHAIN)/*/bin $(STAGING_SUBDIR_TOOLCHAIN)/libexec \
+		-type f | $(XARGS) $(SCRIPT_DIR)/bundle-libraries.sh $(SDK_BUILD_DIR)/$(STAGING_SUBDIR_HOST))
+
 	@-( \
 		find \
 			$(SDK_BUILD_DIR)/$(STAGING_SUBDIR_HOST)/bin \