diff options
Diffstat (limited to 'third_party/rust/getrandom/src/util_libc.rs')
| -rw-r--r-- | third_party/rust/getrandom/src/util_libc.rs | 160 |
1 files changed, 160 insertions, 0 deletions
diff --git a/third_party/rust/getrandom/src/util_libc.rs b/third_party/rust/getrandom/src/util_libc.rs new file mode 100644 index 0000000000..d057071a74 --- /dev/null +++ b/third_party/rust/getrandom/src/util_libc.rs @@ -0,0 +1,160 @@ +// Copyright 2019 Developers of the Rand project. +// +// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or +// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license +// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. +#![allow(dead_code)] +use crate::Error; +use core::{ + 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 = "redox"))] { + 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(all(target_os = "horizon", target_arch = "arm"))] { + 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; + } +} + +cfg_if! { + if #[cfg(target_os = "vxworks")] { + use libc::errnoGet as get_errno; + } else if #[cfg(target_os = "dragonfly")] { + // Until rust-lang/rust#29594 is stable, we cannot get the errno value + // on DragonFlyBSD. So we just return an out-of-range errno. + unsafe fn get_errno() -> libc::c_int { -1 } + } 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 [u8], + sys_fill: impl Fn(&mut [u8]) -> libc::ssize_t, +) -> Result<(), Error> { + while !buf.is_empty() { + let res = sys_fill(buf); + if res < 0 { + 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); + } + } else { + // We don't check for EOF (ret = 0) as the data we are reading + // should be an infinite stream of random bytes. + buf = &mut buf[(res as usize)..]; + } + } + 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) + } + } + } +} + +cfg_if! { + if #[cfg(any(target_os = "linux", target_os = "emscripten"))] { + use libc::open64 as open; + } else { + use libc::open; + } +} + +// 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 = 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); + } + } +} |