debug build on M1 CPU: large arrays on stack fail with fatal runtime error: stack overflow

[smoothdeveloper]

I tried this code:

    #[test]
    pub fn notpass() {
        let t = [0f32;526398];
        for i in 1 .. 20 {
            println!("{}", t[i]);
        }
    }

It crashes with

thread 'checkptrcast::tests::notpass' has overflowed its stack
fatal runtime error: stack overflow

when testing without the --release flag.

I'm running on Mac M1 and not tried yet on x64 architecture.

I'm looking to allocate much larger multidimensional array in the actual code and not sure how to proceed to make it work in debug builds.

Not sure if this is related: #40862 and if something could be done to help users troubleshooting this if the limitation in the compiler can't be fixed; maybe it could warn that the stack size is going to blow on the target arch?

warning: a stack allocated array of size X is defined here but it may panic at runtime on the Y target architecture.

or maybe not even compile and provide the user with approaches to replace usage of stack allocated array.

[smoothdeveloper]

Context: I was trying to convert C++ code which deals with a pointer to a class instance member being such large array, although in that code, the array isn't allocated on the stack (class is "newed").

I've been pointed at bytemuck and cast_vec for working around the issue I'm dealing with in the code.

Is it worth it/possible for the compiler to emit a warning?

[hkratz]

@smoothdeveloper You are explicitly creating the array on the stack. The testing framework creates threads for multi-threaded testing and the default stack size for threads created from within Rust is 2 MiB. So this will predictably fail on all architectures.

@rustbot label -O-ARM -O-macos

[Enselic]

Triage: Thanks for reporting. No matter what stack size is default, it will always be too small for someone. In this case it should work to make it bigger with RUST_MIN_SIZE. Let's close this.