build: explicitly whitelist symbols in NetworkManager binary

- this allows the linker to drop unused symbols via link-time optimization
  or with --gc-sections:

    git clean -fdx
    ./autogen.sh --enable-ld-gc --enable-ifcfg-rh --enable-ifupdown \
        --enable-ifnet --enable-ibft --enable-teamdctl --enable-wifi \
        --with-modem-manager-1 --with-ofono --with-more-asserts \
        --with-more-logging
    make -j20
    strip ./src/NetworkManager

  gives 2822840 vs. 2625960 bytes (-7%).

- this also gives more control over the symbols that are used by the
  plugins. Yes, it means if you modify a plugin to use a new symbols,
  you have to extend NetworkManager.ver file.
  You can run the script to create the version file:

    $ ./tools/create-exports-NetworkManager.sh update

  but be sure that your current configuration enables all plugins
  and debugging options to actually use all symbols that are in use.

- If you compile with certain plugins enabled, you could theoretically
  re-compile NetworkManager to expose less symbols. Try:

    $ ./tools/create-exports-NetworkManager.sh build

- note that we have `make check` tests to ensure that all used
  symbols of the plugins can be found. So, it should not be possible
  to accidentally forget to expose a symbol.

1 files changed, 104 insertions, 0 deletions

diff --git a/tools/create-exports-NetworkManager.sh b/tools/create-exports-NetworkManager.sh
new file mode 100755
index 0000000000..f0cdd419f9
--- /dev/null
+++ b/tools/create-exports-NetworkManager.sh
@@ -0,0 +1,104 @@
+#!/bin/bash
+
+set -e
+
+# generates the linker version script src/NetworkManager.ver
+# by looking at the symbols needed by the device and settings
+# plugins. Note that this depends on how NetworkManager and
+# the plugins are build. For example, compiling without
+# --with-more-asserts will yield less symbols.
+#
+# _build re-builds NetworkManager with relevant compile time
+# options to yield the most symbols.
+_build() {
+    git clean -fdx
+    ./autogen.sh --enable-ld-gc --enable-ifcfg-rh --enable-ifupdown \
+        --enable-ifnet --enable-ibft --enable-teamdctl --enable-wifi \
+        --with-modem-manager-1 --with-ofono --with-more-asserts \
+        --with-more-logging
+    make -j20
+}
+
+_sort() {
+    LANG=C sort -u
+}
+
+call_nm() {
+    nm "$1" |
+        sed -n 's/^................ \(.\) \(.*\)$/\1 \2/p'
+}
+
+get_symbols_nm () {
+    call_nm ./src/NetworkManager |
+        sed -n 's/^[tTDR] //p' |
+        _sort
+}
+
+get_symbols_explict() {
+    cat <<EOF | _sort
+_IO_stdin_used
+EOF
+}
+
+get_symbols_missing() {
+    (for f in ./src/settings/plugins/*/.libs/*.so ./src/devices/*/.libs/*.so; do
+        call_nm "$f" |
+            sed -n 's/^\([U]\) \(\(nm_\|nmp_\|_nm\|NM\|_NM\).*\)$/\2/p'
+    done) |
+        _sort |
+        grep -Fx -f <(get_symbols_explict) -v |
+        grep -Fx -f <(get_symbols_nm)
+}
+
+pretty() {
+    sed 's/.*/\t\0;/'
+}
+
+do_build() {
+    do_update
+    touch src/main.c
+    make
+}
+
+do_rebuild() {
+    _build
+    do_build
+}
+
+do_update() {
+    do_generate > ./src/NetworkManager.ver
+}
+
+do_generate() {
+    cd "$(realpath $(dirname "$0"))/.."
+    test -f ./src/NetworkManager
+
+    cat <<EOF
+# this file is generated by $0
+{
+global:
+$(get_symbols_missing | pretty)
+
+$(get_symbols_explict | pretty)
+local:
+	*;
+};
+EOF
+}
+
+
+case "$1" in
+    rebuild)
+        do_rebuild
+        ;;
+    build)
+        do_build
+        ;;
+    update)
+        do_update
+        ;;
+    *)
+        do_generate
+        ;;
+esac
+