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Bug 4273

Summary: Android: nativeRunMain(): Couldn’t find function SDL_main in library
Product: SDL Reporter: ZZ <registrirayme>
Component: mainAssignee: Sam Lantinga <slouken>
Status: RESOLVED INVALID QA Contact: Sam Lantinga <slouken>
Severity: blocker    
Priority: P1 CC: sylvain.becker
Version: 2.0.8   
Hardware: ARM   
OS: Android (All)   

Description ZZ 2018-09-26 06:20:23 UTC 
I have an issue similar to the one described here on Android:
https://github.com/urho3d/Urho3D/issues/2267

I have main() in a static library which I link to the main .so. I tried different variants but whenever the static library (with main()) is linked to a dynamic library I get the error message:
nativeRunMain(): Couldn’t find function SDL_main in library

The proposed solution in that engine in the link above doesn't work for me:
extern "C" __attribute__((visibility("default"))) int SDL_main(int argc, char** argv); \
int SDL_main(int argc, char** argv) \
Comment 1 Sylvain 2018-09-27 10:34:59 UTC 
Could this be the same at bug #4002 ?
I would say no, because in that case this is the library which cannot be found.

use objdump on your build libraries:

objdump -T build/intermediates/ndkBuild/release/obj/local/arm64-v8a/libmain.so | grep main

gives:

00000000000ca508 g    DF .text	0000000000000128  Base        SDL_main
Comment 2 ZZ 2018-09-28 04:57:40 UTC 
I don't think that the above bug is anything like this one. From what I've read is that SDL_main get's stripped as unused during linking.
My project has the following structure:
1. executable
2. engine library (dynamic)
3. sdl library (dynamic)
4. a static library that containts int main() (thus contains SDL_main)
In that configuration compiled with MSVC and Clang on Windows, and GCC on Linux it works. On Android on the other hand I get the above error message.

The workaround I found was to compile libraries 2 and 3 as static and to link them to the executable like that (I use CMake):
target_link_libraries (${PROJECT_NAME}
  # Prevent SDL_main from being stripped when linked in a static library
  $<$<PLATFORM_ID:Android>:-Wl,--whole-archive>
  Engine_main
  $<$<PLATFORM_ID:Android>:-Wl,--no-whole-archive>
)
Comment 3 ZZ 2018-09-28 05:09:13 UTC 
I missed an important bit of information. I am using NDK r18 and the target arm64-v8a.
While the above workaround helps it is not optimal because it limits flexibility.
Comment 4 Sam Lantinga 2018-09-28 08:12:08 UTC 
Yes, if you have a static library, you're only guaranteed to link in the functions that are actually referenced by your executable.

One way to guarantee that you pull it in is to have a static function pointer in your executable that points to the function.