How much stack space should Windows reserve for stack overflow exceptions?

[ChrisDenton]

We reserve some stack space for handling stack overflow exceptions. Our exception handler just prints a stack overflow message along with the thread name. Currently we reserve ~20kb of stack:

https://github.com/rust-lang/rust/blob/903d2976fdb6ceeb65526b7555d8d1e6f8c02134/library/std/src/sys/pal/windows/stack_overflow.rs#L8C59-L8C65

This number is somewhat arbitrary and was chosen over a decade ago, pre-1.0, when Rust was a very different language. That said, we set the main thread to have a stack size of 1mb by default so 20kb is just a few percent of it. Still, sometimes every byte counts and I think it would be useful to have some kind of rationale for the number (e.g. is, say, 4kb not enough?).

[ChrisDenton]

We currently use 8KiB of stack space for UTF-8 to UTF-16 conversion when printing to the console.

rust/library/std/src/sys/pal/windows/stdio.rs

Line 61 in 903d297

const MAX_BUFFER_SIZE: usize = 8192;

rust/library/std/src/sys/pal/windows/stdio.rs

Line 171 in 903d297

let mut utf16 = [MaybeUninit::<u16>::uninit(); MAX_BUFFER_SIZE / 2];

So either we need at least 8 KiB + some_number or else we should not use so much stack space when panicking. Probably the latter would be good.

[jyn514]

that buffer is only used when writing to the console, right? and it’s ok to do partial writes and have the caller retry. so we could probably chop the size down pretty significantly if we’re willing to make printing it the console slightly slower.

[ChrisDenton]

Yeah, we could even just use a smaller buffer when printing runtime messages.