GDScript: Suppress -Wdangling-pointer warning for Linux Arm64 release templates

[Rafael-Petry]

What problem(s) does this PR solve?

• Closes The GDScript module raises a -Wdangling-pointer warning for Linux Arm64 release templates #118150

Additional information

It changes the declaration of the call_level variable to be inside the enter_function method, using the memnew function (it is freed on the exit_function method, using memdelete). It also changes the enter_function's signature, as the call_level pointer is not passed as a parameter anymore.

No AI assistance was used on this PR.

This is also my first PR, so any considerations are very much welcome :)

Tests

• Ran scons target=template_release werror=yes and it finished compiling
• Ran a simple recursion script to make sure no stack underflow/overflow bugs or memory leaks were introduced

[HolonProduction]

What I meant by suppressing in my comment on the issue was actually just applying one of our warning suppression macros e.g. GODOT_GCC_WARNING_IGNORE.

Warnings are meant to help us, but if they do get in the way there is no need to jump through hoops for them. In this case I see no reason to switching to a dedicated heap allocation. The VM code ensures that the lifetime of this pointer does not exceed the lifetime of the stack allocated call level, it's just a bit too complicated for the compiler to recognize.

There might be a point against relying on such complicated contracts, but for the GDScript VM I think it's worth it.

[Rafael-Petry]

I must've missed the existence of these macros while looking through the codebase, this is definitely a more reasonable approach.

Just fixed my changes accordingly. Thanks for the tip!

[NoctemCat]

Maybe runners use older GCC, so that's why it errors? Not fully sure. The error from CI checks:

 ./core/typedefs.h:310:37: error: unknown option after '#pragma GCC diagnostic' kind [-Werror=pragmas]

I think you can try to see if

	GDScriptLanguage::CallLevel call_level;
	GDScriptLanguage::CallLevel* call_level_ptr = &call_level; // Suppress -Wdangling-pointer GCC warning.
	GDScriptLanguage::get_singleton()->enter_function(call_level_ptr, p_instance, this, stack, &ip, &line);

will also suppress it.

[Rafael-Petry]

I tested your idea and it didn't work unfortunately, it raised the initial dangling pointer warning.

You were correct on the version mismatch of the runner though. The build-linux job runs on ubuntu-22.04, which uses gcc-11 by default. The -Wdangling-pointer warning was introduced on gcc-12 (as stated on the GCC Warning History wiki), which explains why the runner fails to recognize it. I also confirmed this is true by compiling on the different versions locally.

Therefore, I think the way to go would be to just check if the GCC version >= 12 before using the suppressing macros, such as:

#if defined(__GNUC__) && !defined(__clang__) && __GNUC__ >= 12
		GODOT_GCC_WARNING_PUSH_AND_IGNORE("-Wdangling-pointer") // The VM ensures call_level is not freed while it is in use, so this warning is a false positive for GCC 12+.
#endif

		_call_stack = call_level;

#if defined(__GNUC__) && !defined(__clang__) && __GNUC__ >= 12
		GODOT_GCC_WARNING_POP
#endif

If that is a good approach, for what I could see, it both fixes the warning issue when compiling with more recent versions of GCC and also doesn't break compilation for older versions.

Thanks!

[HolonProduction]

LGTM to me beside the comment nitpick 👍

Not exactly an expert on this whole gcc macro stuff, but it seems sane to me and passes CI, so it should be fine.

[Repiteo]

Thanks! Congratulations on your first merged contribution! 🎉