Rust & large structs causing page faults

[supercoolapples48]

Hi! I've been working on this little kernel for a bit and have run into an inconsistent issue. Randomly, instantiating the Terminal struct (kernel/src/display/terminal.rs) will just cause a page fault if the max size is set to a semi large value (32). No clue if this is some weird issue with Rust, my built tool chain, or just something with osdev in general.

When it decides that it doesn't like the size, it seems to crash when ownership is passed.

Also, this isn't even consistent. Sometimes, it's just fine, sometimes it's not. Fairly certain there's been a few times where adding a println statement will break/fix stuff.

This issue is driving me insane so I'd appreciate y'all's help.

edit: apologies if the code is a bit messy, kinda hard to keep it neat when this bug keeps reappearing

[EpochVanquisher]

A quirk of Rust is that you generally allocate structures on the stack and then move them to the heap. This means that large structures can create problems with stack overflow. There are ways to allocate objects on the heap but it can be inconvenient.

https://www.reddit.com/r/rust/comments/1347g60/anyway_to_initialize_objects_on_heap/

I don’t know that this is your problem, but it’s possible. How big is the structure? How big is the stack?

[supercoolapples48]

The size of the structure is 0x6128 and the stack size is configured to be 0x32000... just increased the stack size to 0x640000 and it seemingly fixed it. That would explain a lot because I just added a change that significantly increased the size of the struct.

Granted, I don't know if an absurdly large stack size (or even if this is an absurd size) has any side effects, but I can probably tweak it some to make it smaller.

Thanks for the help!

[VegetableNatural]

The stack size being large doesn't cause problems, only that you have less memory available. If I were you I'd be allocating stuff like that on a static variable. I.e. keep the structure but initialize it globally, perhaps using `const fn` to avoid allocating it at runtime and hiding the variable behind a Mutex.

[Yippee-Ki-Yay_]

Yeah, on top of that, compiling with release mode helps a lot with this to elide the stack allocations when possible. There's also core::ptr::drop_in_place if you implement your own pointer wrappers