build: add symbol versioning for SDL

If a program built against one version of SDL is run in an
environment where there is an earlier version of the SDL .so library
installed, the result varies depending on platform configuration; in
the best case, it won't start at all, at worst it aborts in the
middle of the user doing "something important" (systems implementing
lazy symbol resolution). verdefs on the other hand are always checked
on startup.

The dependency information present in programs and shared libraries
is not only of value to the dynamic linker, but also to a
distribution's package management. If the dynamic linker is able to
tell that a program is not runnable per the above, a package manager
is able to come to the same conclusion — and block the installation
of a nonfunctional program+library ensemble.

Because there are a lot more symbols than there are libraries (I am
going to throw in "10^4 to 1 or worse"), package managers generally
do not evaluate symbols, but only e.g. the SONAME, NEEDED and VERNEED
fields/blocks. Because the SONAME is the same between two SDL
versions like 2.0.24, and 2.0.26, everything rests on having verdefs.

This patch proposes the addition of verdefs.

Android.mk

@@ -80,7 +80,7 @@ LOCAL_CFLAGS += -Wno-unused-parameter -Wno-sign-compare
 
 LOCAL_LDLIBS := -ldl -lGLESv1_CM -lGLESv2 -lOpenSLES -llog -landroid
 
-LOCAL_LDFLAGS := -Wl,--no-undefined
+LOCAL_LDFLAGS := -Wl,--no-undefined -Wl,--version-script=$(LOCAL_PATH)/src/dynapi/SDL_dynapi.sym
 
 ifeq ($(NDK_DEBUG),1)
     cmd-strip :=

CMakeLists.txt

@@ -276,6 +276,15 @@ if(WINDOWS)
   set(CMAKE_SHARED_LIBRARY_PREFIX "")
 endif()
 
+check_linker_flag(C "-Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/src/dynapi/SDL_dynapi.sym" HAVE_WL_VERSION_SCRIPT)
+if(HAVE_WL_VERSION_SCRIPT)
+  list(APPEND EXTRA_LDFLAGS_BUILD "-Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/src/dynapi/SDL_dynapi.sym")
+else()
+  if((LINUX AND LIBC_IS_GLIBC) OR ANDROID)
+    message(FATAL_ERROR "Linker does not support '-Wl,--version-script=xxx.sym'. This is required on the current host platform (${SDL_CMAKE_PLATFORM}).")
+  endif()
+endif()
+
 # Emscripten toolchain has a nonempty default value for this, and the checks
 # in this file need to change that, so remember the original value, and
 # restore back to that afterwards. For check_function_exists() to work in
@@ -3182,6 +3191,8 @@ if(SDL_SHARED)
   # alias target for in-tree builds
   add_library(SDL3::SDL3 ALIAS SDL3)
   set_target_properties(SDL3 PROPERTIES POSITION_INDEPENDENT_CODE TRUE)
+  set_target_properties(SDL3 PROPERTIES LINK_DEPENDS "${CMAKE_CURRENT_SOURCE_DIR}/src/dynapi/SDL_dynapi.sym")
+  set_target_properties(SDL3 PROPERTIES INTERFACE_LINK_DEPENDS "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src/dynapi/SDL_dynapi.sym>")
   if(NOT SDL_LIBC)
     if(MSVC AND SDL_CPU_X86)
       # FIXME: should be added for all architectures (missing symbols for ARM)

cmake/macros.cmake

@@ -110,6 +110,26 @@ else()
   endif()
 endif()
 
+if(CMAKE_VERSION VERSION_LESS 3.18)
+  function(check_linker_flag LANG FLAG VAR)
+    cmake_push_check_state()
+    list(APPEND CMAKE_REQUIRED_LINK_OPTIONS ${FLAG} )
+    if(LANG STREQUAL "C")
+      include(CheckCSourceCompiles)
+      check_c_source_compiles("int main(int argc,char*argv[]){(void)argc;(void)argv;return 0;}" ${VAR} FAIL_REGEX "warning")
+    elseif(LANG STREQUAL "CXX")
+      include(CheckCXXSourceCompiles)
+      check_cxx_source_compiles("int main(int argc,char*argv[]){(void)argc;(void)argv;return 0;}" ${VAR} FAIL_REGEX "warning")
+    else()
+      message(FATAL_ERROR "Unsupported language: ${LANG}")
+    endif()
+    cmake_pop_check_state()
+  endfunction()
+else()
+  cmake_policy(SET CMP0057 NEW)  # Support new if() IN_LIST operator. (used inside check_linker_flag, used in CMake 3.18)
+  include(CheckLinkerFlag)
+endif()
+
 if(APPLE)
   check_language(OBJC)
   if(NOT CMAKE_OBJC_COMPILER)

src/dynapi/gendynapi.pl

@@ -33,6 +33,7 @@ use File::Basename;
 chdir(dirname(__FILE__) . '/../..');
 my $sdl_dynapi_procs_h = "src/dynapi/SDL_dynapi_procs.h";
 my $sdl_dynapi_overrides_h = "src/dynapi/SDL_dynapi_overrides.h";
+my $sdl_dynapi_sym = "src/dynapi/SDL_dynapi.sym";
 
 my %existing = ();
 if (-f $sdl_dynapi_procs_h) {
@@ -48,6 +49,10 @@ if (-f $sdl_dynapi_procs_h) {
 open(SDL_DYNAPI_PROCS_H, '>>', $sdl_dynapi_procs_h) or die("Can't open $sdl_dynapi_procs_h: $!\n");
 open(SDL_DYNAPI_OVERRIDES_H, '>>', $sdl_dynapi_overrides_h) or die("Can't open $sdl_dynapi_overrides_h: $!\n");
 
+open(SDL_DYNAPI_SYM, '<', $sdl_dynapi_sym) or die("Can't open $sdl_dynapi_sym: $!\n");
+read(SDL_DYNAPI_SYM, my $sdl_dynapi_sym_contents, -s SDL_DYNAPI_SYM);
+close(SDL_DYNAPI_SYM);
+
 opendir(HEADERS, 'include/SDL3') or die("Can't open include dir: $!\n");
 while (my $d = readdir(HEADERS)) {
     next if not $d =~ /\.h\Z/;
@@ -76,6 +81,8 @@ while (my $d = readdir(HEADERS)) {
 
             next if $existing{$fn};   # already slotted into the jump table.
 
+            $sdl_dynapi_sym_contents =~ s/# extra symbols go here/$fn;\n    # extra symbols go here/;
+
             my @params = split(',', $7);
 
             #print("rc == '$rc', fn == '$fn', params == '$params'\n");
@@ -144,4 +151,8 @@ closedir(HEADERS);
 close(SDL_DYNAPI_PROCS_H);
 close(SDL_DYNAPI_OVERRIDES_H);
 
+open(SDL_DYNAPI_SYM, '>', $sdl_dynapi_sym) or die("Can't open $sdl_dynapi_sym: $!\n");
+print SDL_DYNAPI_SYM $sdl_dynapi_sym_contents;
+close(SDL_DYNAPI_SYM);
+
 # vi: set ts=4 sw=4 expandtab: