CharString variable declaration in GDNative code causes crash when that method is called from GDScript

[todd-koeck]

Godot version

3.5.1.stable

System information

WIndows 10

Issue description

When a CharString variable is declared in a C++ method called by GDScript, Godot will crash shortly after, possibly during, the return from the called C++ method.

I think this was crashing under linux as well, but most of my testing and debugging of this crash was performed under windoze.

I ran into the problem on another project where I was initially using a CharString to convert a Godot::String to a C/C++ string before I found String::alloc_c_string(). However, I left the CharString declaration in that code and was getting random crashes on the first call, unless I had a print() statement immediately before it in the calling GDScript code. Once I removed the declaration of the unused CharString variable, the crashes stopped.

To verify that removing the CharString variable declaration was really a fix, I added one to the GDNative C++ Example code. That code now crashes as well.

Steps to reproduce

Start with the GDExample class in the GDNative C++ Example tutorial. Declare a CharString variable in the _process() method:

void GDExample::_process(float delta) {
  CharString cs;                          // <------- Added this line
  time_passed += speed * delta;

  Vector2 new_position = Vector2(
				 (real_t) (amplitude + (amplitude * sin(time_passed * 2.0))),
				 (real_t) (amplitude + (amplitude * cos(time_passed * 1.5)))
				 );

  set_position(new_position);
}

Build the code.

Run the main.tscn scene.

It should crash.

Minimal reproduction project

GDNative C++ Example

[todd-koeck]

The GDNative C++ Example crashes under linux (debian 11.3) as well. However, I get a backtrace there, which I didn't when it crashed under windoze.

================================================================
handle_crash: Program crashed with signal 11
Engine version: Godot Engine v3.5.1.stable.official (6fed1ffa313c6760fa88b368ae580378daaef0f0)
Dumping the backtrace.

Please include this when reporting the bug on: https://github.com/godotengine/godot/issues
[1] /lib/x86_64-linux-gnu/libc.so.6(+0x3bd60) [0x7fc1e4717d60] (??:0)
[2] .../Godot_v3.5.1-stable_x11.64() [0x10dbfb8] (??:0)
[3] godot::CharString::~CharString() (??:0)
[4] godot::GDExample::_process(float) (??:0)
[5] godot_variant godot::__wrapped_method<godot::GDExample, void, float>(void*, void*, void*, int, godot_variant**) (??:0)
[6] .../Godot_v3.5.1-stable_x11.64() [0xed8298] (??:0)
[7] .../Godot_v3.5.1-stable_x11.64() [0x1f835ef] (??:0)
[8] .../Godot_v3.5.1-stable_x11.64() [0x24bc7d0] (??:0)
[9] .../Godot_v3.5.1-stable_x11.64() [0x1fad99e] (??:0)
[10] .../Godot_v3.5.1-stable_x11.64() [0x1fe3429] (??:0)
[11] .../Godot_v3.5.1-stable_x11.64() [0xa91d0a] (??:0)
[12] .../Godot_v3.5.1-stable_x11.64() [0xa0240d] (??:0)
[13] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xea) [0x7fc1e4702d0a] (??:0)
[14] .../Godot_v3.5.1-stable_x11.64() [0xa14e0e] (??:0)
-- END OF BACKTRACE --
================================================================

[Zylann]

Note: godotengine/godot-cpp#842