Rust - Is the stack size different for debug vs. release mode?

Question

Consider the following program:

fn recursive_call(x: u32) -> u32 {
    println!("x: {:?}", x);
    recursive_call(x +1)
}

fn main() {
    recursive_call(0);
}

When I run cargo build && ./target/debug/recursive_call, this crashes after x: 58152:

x: 58152

thread 'main' has overflowed its stack
fatal runtime error: stack overflow
Aborted (core dumped)

while when I run cargo build --release && ./target/release/recursive_call, this crashes only after x: 104728:

x: 104728

thread 'main' has overflowed its stack
[...]

I wondering where this difference in behavior comes from? Is the stack size different in release vs. debug mode? Or is this because of some compile time optimizations I am missing (if so, what would so optimizations be?)

Answer 1

The stack size is the same for debug and release (and unless you have threads, the stack size is actually fixed by the OS, see eg. ulimit -s on Linux). However the stack usage may be different because in debug mode the compiler adds some data to each stack frame to help debuggers find local variables.

Note that tail-call optimization may cause the compiler to remove the recursion and allow an infinite loop in release mode.

Answer 2

Yep, according to Godbolt on x86-64 the reserved stacksize for the function in debug mode is 120 bytes, with optimizations turned on (-O) it is 72 bytes. That is quite normal.