#![allow(dead_code)]
use crate::Error;
use core::{
mem::MaybeUninit,
num::NonZeroU32,
ptr::NonNull,
sync::atomic::{fence, AtomicPtr, Ordering},
};
use libc::c_void;
cfg_if! {
if #[cfg(any(target_os = "netbsd", target_os = "openbsd", target_os = "android"))] {
use libc::__errno as errno_location;
} else if #[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "hurd", target_os = "redox", target_os = "dragonfly"))] {
use libc::__errno_location as errno_location;
} else if #[cfg(any(target_os = "solaris", target_os = "illumos"))] {
use libc::___errno as errno_location;
} else if #[cfg(any(target_os = "macos", target_os = "freebsd"))] {
use libc::__error as errno_location;
} else if #[cfg(target_os = "haiku")] {
use libc::_errnop as errno_location;
} else if #[cfg(target_os = "nto")] {
use libc::__get_errno_ptr as errno_location;
} else if #[cfg(any(all(target_os = "horizon", target_arch = "arm"), target_os = "vita"))] {
extern "C" {
// Not provided by libc: https://github.com/rust-lang/libc/issues/1995
fn __errno() -> *mut libc::c_int;
}
use __errno as errno_location;
} else if #[cfg(target_os = "aix")] {
use libc::_Errno as errno_location;
}
}
cfg_if! {
if #[cfg(target_os = "vxworks")] {
use libc::errnoGet as get_errno;
} else {
unsafe fn get_errno() -> libc::c_int { *errno_location() }
}
}
pub fn last_os_error() -> Error {
let errno = unsafe { get_errno() };
if errno > 0 {
Error::from(NonZeroU32::new(errno as u32).unwrap())
} else {
Error::ERRNO_NOT_POSITIVE
}
}
// Fill a buffer by repeatedly invoking a system call. The `sys_fill` function:
// - should return -1 and set errno on failure
// - should return the number of bytes written on success
pub fn sys_fill_exact(
mut buf: &mut [MaybeUninit<u8>],
sys_fill: impl Fn(&mut [MaybeUninit<u8>]) -> libc::ssize_t,
) -> Result<(), Error> {
while !buf.is_empty() {
let res = sys_fill(buf);
match res {
res if res > 0 => buf = buf.get_mut(res as usize..).ok_or(Error::UNEXPECTED)?,
-1 => {
let err = last_os_error();
// We should try again if the call was interrupted.
if err.raw_os_error() != Some(libc::EINTR) {
return Err(err);
}
}
// Negative return codes not equal to -1 should be impossible.
// EOF (ret = 0) should be impossible, as the data we are reading
// should be an infinite stream of random bytes.
_ => return Err(Error::UNEXPECTED),
}
}
Ok(())
}
// A "weak" binding to a C function that may or may not be present at runtime.
// Used for supporting newer OS features while still building on older systems.
// Based off of the DlsymWeak struct in libstd:
// https://github.com/rust-lang/rust/blob/1.61.0/library/std/src/sys/unix/weak.rs#L84
// except that the caller must manually cast self.ptr() to a function pointer.
pub struct Weak {
name: &'static str,
addr: AtomicPtr<c_void>,
}
impl Weak {
// A non-null pointer value which indicates we are uninitialized. This
// constant should ideally not be a valid address of a function pointer.
// However, if by chance libc::dlsym does return UNINIT, there will not
// be undefined behavior. libc::dlsym will just be called each time ptr()
// is called. This would be inefficient, but correct.
// TODO: Replace with core::ptr::invalid_mut(1) when that is stable.
const UNINIT: *mut c_void = 1 as *mut c_void;
// Construct a binding to a C function with a given name. This function is
// unsafe because `name` _must_ be null terminated.
pub const unsafe fn new(name: &'static str) -> Self {
Self {
name,
addr: AtomicPtr::new(Self::UNINIT),
}
}
// Return the address of a function if present at runtime. Otherwise,
// return None. Multiple callers can call ptr() concurrently. It will
// always return _some_ value returned by libc::dlsym. However, the
// dlsym function may be called multiple times.
pub fn ptr(&self) -> Option<NonNull<c_void>> {
// Despite having only a single atomic variable (self.addr), we still
// cannot always use Ordering::Relaxed, as we need to make sure a
// successful call to dlsym() is "ordered before" any data read through
// the returned pointer (which occurs when the function is called).
// Our implementation mirrors that of the one in libstd, meaning that
// the use of non-Relaxed operations is probably unnecessary.
match self.addr.load(Ordering::Relaxed) {
Self::UNINIT => {
let symbol = self.name.as_ptr() as *const _;
let addr = unsafe { libc::dlsym(libc::RTLD_DEFAULT, symbol) };
// Synchronizes with the Acquire fence below
self.addr.store(addr, Ordering::Release);
NonNull::new(addr)
}
addr => {
let func = NonNull::new(addr)?;
fence(Ordering::Acquire);
Some(func)
}
}
}
}
// SAFETY: path must be null terminated, FD must be manually closed.
pub unsafe fn open_readonly(path: &str) -> Result<libc::c_int, Error> {
debug_assert_eq!(path.as_bytes().last(), Some(&0));
loop {
let fd = libc::open(path.as_ptr() as *const _, libc::O_RDONLY | libc::O_CLOEXEC);
if fd >= 0 {
return Ok(fd);
}
let err = last_os_error();
// We should try again if open() was interrupted.
if err.raw_os_error() != Some(libc::EINTR) {
return Err(err);
}
}
}
/// Thin wrapper around the `getrandom()` Linux system call
#[cfg(any(target_os = "android", target_os = "linux"))]
pub fn getrandom_syscall(buf: &mut [MaybeUninit<u8>]) -> libc::ssize_t {
unsafe {
libc::syscall(
libc::SYS_getrandom,
buf.as_mut_ptr() as *mut libc::c_void,
buf.len(),
0,
) as libc::ssize_t
}
}
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