Add (and require) version scripts for everything.

Author: DanAlbert

README.md

@@ -86,6 +86,25 @@ above:
 5. Android Studio can warn you and auto-fix common mistakes in class names and
    function signatures.
 
+### Version scripts
+
+All of the app libraries shown here are built using a version script. This is a
+file that explicitly lists which symbols should be exported from the library,
+and hides all the others. Version scripts function similarly to
+`-fvisibility=hidden`, but can go a step further and are capable of hiding
+symbols in static libraries that are used by your app. Hiding as many symbols as
+possible results in smaller binaries that load faster, as there are fewer
+relocations required and LTO can do a better job. There are no good reasons to
+not use a version script for your NDK code. See the NDK documentation on
+[controlling symbol visibility] for more information.
+
+You can find these in each sample as the `lib<name>.map.txt` file (where
+`<name>` is the name of the library passed to `add_app_library()` in the
+`CMakeLists.txt` file). The build plumbing that uses the version scripts is in
+the definition of `add_app_library()` in `cmake/AppLibrary.cmake`.
+
+[controlling symbol visibility]: https://developer.android.com/ndk/guides/symbol-visibility
+
 ## Additional documentation
 
 - [Add Native Code to Your Project](https://developer.android.com/studio/projects/add-native-code.html)

audio-echo/app/src/main/cpp/libecho.map.txt

@@ -0,0 +1,6 @@
+LIBECHO {
+  global:
+    JNI_OnLoad;
+  local:
+    *;
+};

bitmap-plasma/app/src/main/cpp/libplasma.map.txt

@@ -0,0 +1,6 @@
+LIBPLASMA {
+  global:
+    JNI_OnLoad;
+  local:
+    *;
+};

camera/basic/src/main/cpp/libndk_camera.map.txt

@@ -0,0 +1,7 @@
+LIBNDK_CAMERA {
+  global:
+    ANativeActivity_onCreate;
+    JNI_OnLoad;
+  local:
+    *;
+};

camera/texture-view/src/main/cpp/libcamera_textureview.map.txt

@@ -0,0 +1,6 @@
+LIBCAMERA_TEXTUREVIEW {
+  global:
+    JNI_OnLoad;
+  local:
+    *;
+};

cmake/AppLibrary.cmake

@@ -3,7 +3,7 @@ include_guard()
 # Wrapper for add_library which enables common options we want for all
 # libraries.
 function(add_app_library name)
-    cmake_parse_arguments(PARSE_ARGV 1 arg "" "" "")
+    cmake_parse_arguments(PARSE_ARGV 1 arg "NO_VERSION_SCRIPT" "" "")
     add_library(${name} ${arg_UNPARSED_ARGUMENTS})
 
     target_compile_options(${name}
@@ -12,4 +12,17 @@ function(add_app_library name)
         -Wextra
         -Werror
     )
+
+    if(NOT arg_NO_VERSION_SCRIPT)
+        target_link_options(${name}
+            PRIVATE
+            -Wl,--no-undefined-version
+            -Wl,--version-script,${CMAKE_SOURCE_DIR}/lib${name}.map.txt
+        )
+
+        set_target_properties(${name}
+            PROPERTIES
+            LINK_DEPENDS ${CMAKE_SOURCE_DIR}/lib${name}.map.txt
+        )
+    endif()
 endfunction()

endless-tunnel/app/src/main/cpp/libgame.map.txt

@@ -0,0 +1,6 @@
+LIBGAME {
+  global:
+    ANativeActivity_onCreate;
+  local:
+    *;
+};

exceptions/app/src/main/cpp/libexceptions.map.txt

@@ -0,0 +1,6 @@
+LIBEXCEPTIONS {
+  global:
+    JNI_OnLoad;
+  local:
+    *;
+};

gles3jni/app/src/main/cpp/libgles3jni.map.txt

@@ -0,0 +1,6 @@
+LIBGLES3JNI {
+  global:
+    JNI_OnLoad;
+  local:
+    *;
+};

hello-gl2/app/src/main/cpp/libgl2jni.map.txt

@@ -0,0 +1,6 @@
+LIBGL2JNI {
+  global:
+    JNI_OnLoad;
+  local:
+    *;
+};