From 2ff14448863ac1a1dd9533461708e29aae170c2d Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Wed, 17 Apr 2024 14:06:31 +0200 Subject: Adding debian version 1.65.0+dfsg1-2. Signed-off-by: Daniel Baumann --- vendor/getrandom/src/util_libc.rs | 57 ++++++++++++++++++++++++++++++--------- 1 file changed, 45 insertions(+), 12 deletions(-) (limited to 'vendor/getrandom/src/util_libc.rs') diff --git a/vendor/getrandom/src/util_libc.rs b/vendor/getrandom/src/util_libc.rs index 6df1cd7da..d057071a7 100644 --- a/vendor/getrandom/src/util_libc.rs +++ b/vendor/getrandom/src/util_libc.rs @@ -6,8 +6,13 @@ // option. This file may not be copied, modified, or distributed // except according to those terms. #![allow(dead_code)] -use crate::{util::LazyUsize, Error}; -use core::{num::NonZeroU32, ptr::NonNull}; +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"))] { @@ -76,29 +81,57 @@ pub fn sys_fill_exact( // 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. -// F must be a function pointer of type `unsafe extern "C" fn`. Based off of the -// weak! macro in libstd. +// 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: LazyUsize, + addr: AtomicPtr, } 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: LazyUsize::new(), + addr: AtomicPtr::new(Self::UNINIT), } } - // Return a function pointer if present at runtime. Otherwise, return null. - pub fn ptr(&self) -> Option> { - let addr = self.addr.unsync_init(|| unsafe { - libc::dlsym(libc::RTLD_DEFAULT, self.name.as_ptr() as *const _) as usize - }); - NonNull::new(addr as *mut _) + // 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> { + // 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) + } + } } } -- cgit v1.2.3