provide an exported symbols list to linker for Apple Mach-O targets

[sezero]

As the $subject says, we should provide an exported symbols list to
linker for Apple Mach-O targets, in order to prevent prevent third-
party symbols from leaking into our library: such may be the case if
we statically link a vendored library to us, e.g. libjxl which leaks
libjxl and brotli symbols into SDL_image.
Reference issue: libsdl-org/libjxl#2

We can generate an exports file at cmake configuration time from the
existing version script file, like below:

set(sdlimage_exports)
file(STRINGS "${CMAKE_CURRENT_SOURCE_DIR}/src/SDL_image.sym" sdlimage_exports_strings)
foreach(sdlimage_export_string ${sdlimage_exports_strings})
  string(STRIP "${sdlimage_export_string}" sdlimage_export_string)
  string(REGEX REPLACE "\;" "" sdlimage_export_string "${sdlimage_export_string}")
  if(sdlimage_export_string MATCHES "IMG_.*")
     # Prepend '_' to symbol name for Mach-O
     set(sdlimage_exports "${sdlimage_exports}_${sdlimage_export_string}\n")
  endif()
endforeach()
file(WRITE "${CMAKE_CURRENT_BINARY_DIR}/SDL_image.exports" "${sdlimage_exports}")

# then add:
#
#    -Wl,-exported_symbols_list,'${CMAKE_CURRENT_BINARY_DIR}/SDL_image.exports'
#
# to linker flags

If we do this, we should do it similary in SDL_mixer and SDL_ttf, too.

Leaving implementation to @madebr

/cc @slouken
/cc @elevenfive

[madebr]

@elevenfive

Does creating a src/SDL_image.exports with the contents at the bottom of this post, and adding the following to the bottom of CMakeLists.txt change anything with your libjxl issues?

if(APPLE)
    target_sources(SDL3_image-shared PRIVATE src/SDL_image.exports)
endif()

`src/SDL_image.exports`

Output of:

cat src/SDL_image.sym | grep IMG_ | cut "-d;" -f 1  | awk '{$1=$1;print "_" $1}'

src/SDL_image.exports

_IMG_FreeAnimation
_IMG_Version
_IMG_Load
_IMG_LoadAVIF_IO
_IMG_LoadAnimation
_IMG_LoadAnimationTyped_IO
_IMG_LoadAnimation_IO
_IMG_LoadBMP_IO
_IMG_LoadCUR_IO
_IMG_LoadGIFAnimation_IO
_IMG_LoadGIF_IO
_IMG_LoadICO_IO
_IMG_LoadJPG_IO
_IMG_LoadJXL_IO
_IMG_LoadLBM_IO
_IMG_LoadPCX_IO
_IMG_LoadPNG_IO
_IMG_LoadPNM_IO
_IMG_LoadQOI_IO
_IMG_LoadSVG_IO
_IMG_LoadSizedSVG_IO
_IMG_LoadTGA_IO
_IMG_LoadTIF_IO
_IMG_LoadTexture
_IMG_LoadTextureTyped_IO
_IMG_LoadTexture_IO
_IMG_LoadTyped_IO
_IMG_LoadWEBPAnimation_IO
_IMG_LoadWEBP_IO
_IMG_LoadXCF_IO
_IMG_LoadXPM_IO
_IMG_LoadXV_IO
_IMG_Load_IO
_IMG_ReadXPMFromArray
_IMG_ReadXPMFromArrayToRGB888
_IMG_SaveJPG
_IMG_SaveJPG_IO
_IMG_SavePNG
_IMG_SavePNG_IO
_IMG_SaveAVIF
_IMG_SaveAVIF_IO
_IMG_isAVIF
_IMG_isBMP
_IMG_isCUR
_IMG_isGIF
_IMG_isICO
_IMG_isJPG
_IMG_isJXL
_IMG_isLBM
_IMG_isPCX
_IMG_isPNG
_IMG_isPNM
_IMG_isQOI
_IMG_isSVG
_IMG_isTIF
_IMG_isWEBP
_IMG_isXCF
_IMG_isXPM
_IMG_isXV
_IMG_SaveTGA
_IMG_SaveTGA_IO
_IMG_SaveGIF
_IMG_SaveGIF_IO
_IMG_SaveWEBP
_IMG_SaveWEBP_IO
_IMG_SaveBMP
_IMG_SaveBMP_IO
_IMG_Save
_IMG_SaveTyped_IO
_IMG_CreateAnimationEncoder
_IMG_CreateAnimationEncoder_IO
_IMG_CreateAnimationEncoderWithProperties
_IMG_AddAnimationEncoderFrame
_IMG_CloseAnimationEncoder
_IMG_LoadAPNGAnimation_IO
_IMG_LoadAVIFAnimation_IO
_IMG_CreateAnimationDecoder
_IMG_CreateAnimationDecoder_IO
_IMG_CreateAnimationDecoderWithProperties
_IMG_GetAnimationDecoderFrame
_IMG_ResetAnimationDecoder
_IMG_CloseAnimationDecoder
_IMG_GetAnimationDecoderProperties
_IMG_GetAnimationDecoderStatus
_IMG_GetClipboardImage
_IMG_CreateAnimatedCursor
_IMG_SaveCUR
_IMG_SaveCUR_IO
_IMG_SaveICO
_IMG_SaveICO_IO
_IMG_SaveAnimation
_IMG_SaveAnimationTyped_IO
_IMG_SaveANIAnimation_IO
_IMG_SaveAPNGAnimation_IO
_IMG_SaveAVIFAnimation_IO
_IMG_SaveGIFAnimation_IO
_IMG_SaveWEBPAnimation_IO

[madebr]

@elevenfive

I'm also not sure how to add the exports file to the linker. Please verify if it is actually used during linking.

If not, do the following instead (of target_sources):

if(APPLE)
  target_link_options(SDL3_image-shared PRIVATE "-Wl,-exported_symbols_list,${PROJECT_SOURCE_DIR}/src/SDL_image.exports")
  set_property(TARGET SDL3_image-shared APPEND PROPERTY LINK_DEPENDS "${PROJECT_SOURCE_DIR}/src/SDL_image.exports")
endif()

[sezero]

not sure how to add the exports file to the linker.

??

Do it like what you already do for version script, no?? E.g. like:

diff --git a/CMakeLists.txt b/CMakeLists.txt
index a2f52d6..284e64e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -336,18 +336,22 @@ if(NOT ANDROID)
         VERSION "${SO_VERSION}"
     )
     if(APPLE)
         cmake_minimum_required(VERSION 3.17...3.28)
         set_target_properties(${sdl3_image_target_name} PROPERTIES
             MACHO_COMPATIBILITY_VERSION "${DYLIB_COMPAT_VERSION}"
             MACHO_CURRENT_VERSION "${DYLIB_CURRENT_VERSION}"
         )
         sdl_no_deprecated_errors(${sdl3_image_target_name})
+        set_property(TARGET ${sdl3_image_target_name} APPEND PROPERTY LINK_DEPENDS
+            "/path/to/SDL_image.exports")
+        target_link_options(${sdl3_image_target_name} PRIVATE
+            "-Wl,-exported_symbols_list,'/path/to/SDL_image.exports'")
     endif()
 endif()
 if(SDLIMAGE_BUILD_SHARED_LIBS)
     if(WIN32)
         set_target_properties(${sdl3_image_target_name} PROPERTIES
             PREFIX ""
             DLL_NAME_WITH_SOVERSION FALSE
         )
     endif()

[madebr]

not sure how to add the exports file to the linker.

??

I now see the suggested link options. Thanks, I'll create a pr tomorrow :)

[sezero]

I now see the suggested link options. Thanks, I'll create a pr tomorrow :)

Should we generate the exports file at configuration time, or should we add it to the source tree and bear a burden of maintaining two files? The latter case is useful for the Xcode project files..

[madebr]

I now see the suggested link options. Thanks, I'll create a pr tomorrow :)

Should we generate the exports file at configuration time, or should we add it to the source tree and bear a burden of maintaining two files? The latter case is useful for the Xcode project files..

I'm thinking about re-using logic from SDL's gendynapy.py.

[sezero]

I'm thinking about re-using logic from SDL's gendynapy.py.

OK. Here are the exports files I generated, in case they help: exports_files.zip