large stack arrays cause segfaults in safe code (even with ulimit unlimited) #34877
Description
Note, first make sure to set ulimit -s unlimited before running the program below.
Something like the following has problems with bad ASM stack offsets/accesses being generated due to 32-bit overflow.
Looks like this is something known in LLVM: https://groups.google.com/forum/#!topic/llvm-dev/g4sF46a47_w
This also only seems to cause segfaults in --release mode
Note however, it's not entirely clear how to easily get a directly heap allocated, large fixed size array without resorting to unsafe, box syntax, or using the vec hack.
I suspect this will come up often as a result, since many people and beginners will attempt to stack allocate a large object only to have it segfault.
Various values can be tweaked to make it not segfault in release or debug, in an entirely unintuitive way, which lends the language a less user friendly feeling, along with violating the principle of least surprise in many cases, imho.
#![feature(box_syntax)]
use std::ops::Index;
use std::ops::IndexMut;
use std::boxed::Box;
// causes problems
//const SIZE: usize = 1300;
const SIZE: usize = 1255;
const BOUND: usize = SIZE;
pub const ARR_SIZE: usize = SIZE * SIZE * BOUND;
struct Arr {
arr: [[[u8; SIZE]; SIZE]; BOUND]
}
impl Arr {
pub fn create () -> Arr {
let x = [0u8; SIZE];
let y = [x; SIZE];
let z = [y; BOUND];
// won't cause problems in release
// Arr { arr: [[[1u8; SIZE]; SIZE]; SIZE] }
Arr { arr: z }
}
}
impl Index<usize> for Arr {
type Output = [[u8; SIZE]; SIZE];
fn index(&self, _index: usize) -> &Self::Output {
&self.arr[_index]
}
}
impl IndexMut<usize> for Arr {
fn index_mut(&mut self, _index: usize) -> &mut [[u8; SIZE]; SIZE] {
&mut self.arr[_index]
}
}
fn main() {
// let mut arr = box Arr::create();
let mut arr = Arr::create();
for i in 0..BOUND {
for j in 0..SIZE {
for k in 0..SIZE {
arr[i][j][k] = (i+j+k) as u8;
}
}
}
/*
for i in 0..SIZE {
for j in 0..SIZE {
for k in 0..SIZE {
println!("{}", arr[i][j][k])
}
}
}
*/
println!("res: {}", arr[1][0][0]);
println!("res: {}", arr[1][SIZE-1][SIZE-1]);
println!("res: {}", arr[1][SIZE-1][SIZE-1]);
}