A function to test that invalid accesses result in SIGSEGV

test_no_perms.rs

#[cfg(target_os = "linux")]
unsafe fn test_no_perms(ptr: *mut u8, read: bool, old_perm: Perm) {
    use libc::{c_int, mprotect, signal, SIGSEGV, size_t};

    static mut got_signal: bool = false;
    static mut __ptr: *mut u8 = 0 as *mut _;

    // reset got_signal back to false after previous call
    let gs_signal = &mut got_signal;
    *gs_signal = false;

    let ptr_ptr = &mut __ptr;
    *ptr_ptr = ptr;

    {
        type HandlerTy = unsafe extern "C" fn(c_int);
        unsafe extern "C" fn handler(signum: c_int) {
            libc::exit(123);
            eprintln!("foobar");
            let gs_signal = &mut got_signal;
            *gs_signal = true;
            mprotect(*__ptr as *mut _, 4096, PROT_READ_WRITE_EXEC);
        }
        signal(libc::SIGSEGV, handler as HandlerTy as usize);

        if read {
            test::black_box(ptr::read_volatile(ptr));
        } else {
            test::black_box(ptr::write_volatile(ptr, 0));
        }
        mprotect(ptr as *mut _, 1, old_perm);
    }

    assert!(got_signal, "didn't get SIGSEGV");
}