Discuss: lazy_static use too much stack space

[fan2nd]

There is a little test program.

use lazy_static::lazy_static;
use std::{
    arch::asm,
    sync::atomic::{AtomicUsize, Ordering},
};

static SP_RECORD: AtomicUsize = AtomicUsize::new(0);

fn get_sp() -> usize {
    let sp: usize;
    unsafe {
        #[cfg(target_arch = "x86_64")]
        asm!("lea {}, [rsp]", out(reg) sp);

        #[cfg(target_arch = "aarch64")]
        asm!("mov {}, sp", out(reg) sp);

        #[cfg(target_arch = "riscv64")]
        asm!("mv {}, sp", out(reg) sp);
    }
    sp
}

const LEN: usize = 1024;

lazy_static! {
    static ref TEST_DATA: [usize; LEN] = {
        SP_RECORD.store(get_sp(), Ordering::Relaxed);
        let mut arr = [0; LEN];
        for i in 0..LEN {
            arr[i] = 2 * i;
        }
        arr
    };
}

fn main() {
    let old_sp = get_sp();
    println!("Old SP: 0x{old_sp:x}");
    let first = TEST_DATA[0];
    let new_sp = SP_RECORD.load(Ordering::Relaxed);
    println!("New SP: 0x{new_sp:x}");
    println!("{first}");
    println!("SP difference: {}", old_sp - new_sp);
}

Then this is the result in release mode.

     Removed 58 files, 1.5MiB total
   Compiling spin v0.9.8
   Compiling lazy_static v1.5.0
   Compiling lazy v0.1.0 (/Users/fan/lazy)
    Finished `release` profile [optimized] target(s) in 0.14s
     Running `target/release/lazy`
Old SP: 0x16b1b2990
New SP: 0x16b1b0970
0
SP difference: 8224

I can not understand. The TEST_DATA should in bss section, why this init funtion used the similar space (8224 <> 8*1024) and did not to edit TEST_DATA directly?

lazy_static! {
    static ref TEST_DATA: [usize; LEN] = {
        ……
    };
}
fn __static_ref_initialize() -> [usize; LEN] {
    ……
}

Is this way below better? Try to pass a mutable reference into __static_ref_initialize.

fn __static_ref_initialize(TEST_DATA: &mut [usize; LEN]) {
    ……
}