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use crate::ffi::CStr;
use crate::marker;
use crate::mem;
use crate::sync::atomic::{AtomicUsize, Ordering};
macro_rules! weak {
    (fn $name:ident($($t:ty),*) -> $ret:ty) => (
        static $name: crate::sys::weak::Weak<unsafe extern fn($($t),*) -> $ret> =
            crate::sys::weak::Weak::new(concat!(stringify!($name), '\0'));
    )
}
pub struct Weak<F> {
    name: &'static str,
    addr: AtomicUsize,
    _marker: marker::PhantomData<F>,
}
impl<F> Weak<F> {
    pub const fn new(name: &'static str) -> Weak<F> {
        Weak { name, addr: AtomicUsize::new(1), _marker: marker::PhantomData }
    }
    pub fn get(&self) -> Option<F> {
        assert_eq!(mem::size_of::<F>(), mem::size_of::<usize>());
        unsafe {
            if self.addr.load(Ordering::SeqCst) == 1 {
                self.addr.store(fetch(self.name), Ordering::SeqCst);
            }
            match self.addr.load(Ordering::SeqCst) {
                0 => None,
                addr => Some(mem::transmute_copy::<usize, F>(&addr)),
            }
        }
    }
}
unsafe fn fetch(name: &str) -> usize {
    let name = match CStr::from_bytes_with_nul(name.as_bytes()) {
        Ok(cstr) => cstr,
        Err(..) => return 0,
    };
    libc::dlsym(libc::RTLD_DEFAULT, name.as_ptr()) as usize
}
#[cfg(not(target_os = "linux"))]
macro_rules! syscall {
    (fn $name:ident($($arg_name:ident: $t:ty),*) -> $ret:ty) => (
        unsafe fn $name($($arg_name: $t),*) -> $ret {
            use super::os;
            weak! { fn $name($($t),*) -> $ret }
            if let Some(fun) = $name.get() {
                fun($($arg_name),*)
            } else {
                os::set_errno(libc::ENOSYS);
                -1
            }
        }
    )
}
#[cfg(target_os = "linux")]
macro_rules! syscall {
    (fn $name:ident($($arg_name:ident: $t:ty),*) -> $ret:ty) => (
        unsafe fn $name($($arg_name:$t),*) -> $ret {
            
            
            use libc::*;
            syscall(
                concat_idents!(SYS_, $name),
                $($arg_name as c_long),*
            ) as $ret
        }
    )
}