Backends: SDL3: Fix gamepad memory leak

[cheyao]

The pointer returned by SDL_GetGamepads should be freed (See: https://wiki.libsdl.org/SDL3/SDL_GetGamepads)

Leak Sanitizer log:

Direct leak of 4 byte(s) in 1 object(s) allocated from:
    #0 0x10479f848 in malloc+0x58 (libclang_rt.lsan_osx_dynamic.dylib:x86_64h+0x33848)
    #1 0x1028887a4 in real_malloc+0x14 (libSDL3.0.dylib:x86_64+0x1037a4)
    #2 0x1028889fb in SDL_malloc_REAL+0x2b (libSDL3.0.dylib:x86_64+0x1039fb)
    #3 0x1027ff5ab in SDL_GetJoysticks_REAL+0x6b (libSDL3.0.dylib:x86_64+0x7a5ab)
    #4 0x1027f9312 in SDL_GetGamepads_REAL+0x22 (libSDL3.0.dylib:x86_64+0x74312)
    #5 0x1027bae08 in SDL_GetGamepads+0x18 (libSDL3.0.dylib:x86_64+0x35e08)
    #6 0x101fee382 in ImGui_ImplSDL3_UpdateGamepads() imgui_impl_sdl3.cpp:643
    #7 0x101fee067 in ImGui_ImplSDL3_NewFrame() imgui_impl_sdl3.cpp:727
    #8 0x101d04c9d in Game::gui() game.cpp:243
    #9 0x101d04afa in Game::iterate() game.cpp:157
    #10 0x101d03114 in SDL_AppIterate main.cpp:79
    #11 0x10280e107 in SDL_IterateMainCallbacks+0x47 (libSDL3.0.dylib:x86_64+0x89107)
    #12 0x102a1efb0 in SDL_EnterAppMainCallbacks_REAL+0xa0 (libSDL3.0.dylib:x86_64+0x299fb0)
    #13 0x1027b972e in SDL_EnterAppMainCallbacks+0x3e (libSDL3.0.dylib:x86_64+0x3472e)
    #14 0x101d02de8 in SDL_main SDL_main_impl.h:59
    #15 0x10280e350 in SDL_RunApp_REAL+0x40 (libSDL3.0.dylib:x86_64+0x89350)
    #16 0x1027d0a03 in SDL_RunApp_DEFAULT+0x33 (libSDL3.0.dylib:x86_64+0x4ba03)
    #17 0x1027beb9e in SDL_RunApp+0x2e (libSDL3.0.dylib:x86_64+0x39b9e)
    #18 0x101d0343e in main SDL_main_impl.h:208
    #19 0x7fff20471f3c in start+0x0 (libdyld.dylib:x86_64+0x15f3c)
its<char>, std::__1::allocator<char> > const&>, std::__1::tuple<> >(std::__1::basic_string<char, std

PS. Maybe the pointer should be cast to a non-const pointer when invoking SDL_free?

[ocornut]

This seems to undo #7807 and #7809 (commit eb72b5a)
Also see libsdl-org/SDL@4961af4

It's very confusing because:

• SDL3 is clearly not up to date.
• We previously made the change linked above but the documentations talks about SDL_GetJoysticks(), NOT SDL_GetGamepads(), they never explicitly state how to handle SDL_GetGamespads() in docs/README-migration.md

But the code is calling SDL_GetJoysticks() and reusing that memory:

SDL_JoystickID *SDL_GetGamepads(int *count)
{
    int num_joysticks = 0;
    int num_gamepads = 0;
    SDL_JoystickID *joysticks = SDL_GetJoysticks(&num_joysticks);
    if (joysticks) {
        int i;
        for (i = num_joysticks - 1; i >= 0; --i) {
            if (SDL_IsGamepad(joysticks[i])) {
                ++num_gamepads;
            } else {
                SDL_memmove(&joysticks[i], &joysticks[i+1], (num_gamepads + 1) * sizeof(joysticks[i]));
            }
        }
    }
    if (count) {
        *count = num_gamepads;
    }
    return joysticks;
}

So I think you have an old version of SDL3 and need to update to latest. SDL3 is currently changing very fast.

[cheyao]

Oh ok! Sorry for the false commit!

[ocornut]

You were right as SDL3 actually reverted their logic on July 27, so actually I was the one not up to date here and needing to revert the imgui backend side change! We're pushing this now.

[ocornut]

Merged as 6a73195. Thank you!