c34fbfaad3
This commit applies rustfmt with rust-lang/rust's default settings to files in src/libstd/sys *that are not involved in any currently open PR* to minimize merge conflicts. THe list of files involved in open PRs was determined by querying GitHub's GraphQL API with this script: https://gist.github.com/dtolnay/aa9c34993dc051a4f344d1b10e4487e8 With the list of files from the script in outstanding_files, the relevant commands were: $ find src/libstd/sys -name '*.rs' \ | xargs rustfmt --edition=2018 --unstable-features --skip-children $ rg libstd/sys outstanding_files | xargs git checkout -- Repeating this process several months apart should get us coverage of most of the rest of the files. To confirm no funny business: $ git checkout $THIS_COMMIT^ $ git show --pretty= --name-only $THIS_COMMIT \ | xargs rustfmt --edition=2018 --unstable-features --skip-children $ git diff $THIS_COMMIT # there should be no difference
56 lines
2 KiB
Rust
56 lines
2 KiB
Rust
//! Support for "weak linkage" to symbols on Unix
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//!
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//! Some I/O operations we do in libstd require newer versions of OSes but we
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//! need to maintain binary compatibility with older releases for now. In order
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//! to use the new functionality when available we use this module for
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//! detection.
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//!
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//! One option to use here is weak linkage, but that is unfortunately only
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//! really workable on Linux. Hence, use dlsym to get the symbol value at
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//! runtime. This is also done for compatibility with older versions of glibc,
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//! and to avoid creating dependencies on GLIBC_PRIVATE symbols. It assumes that
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//! we've been dynamically linked to the library the symbol comes from, but that
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//! is currently always the case for things like libpthread/libc.
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//!
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//! A long time ago this used weak linkage for the __pthread_get_minstack
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//! symbol, but that caused Debian to detect an unnecessarily strict versioned
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//! dependency on libc6 (#23628).
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use crate::ffi::CStr;
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use crate::marker;
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use crate::mem;
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use crate::sync::atomic::{AtomicUsize, Ordering};
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pub struct Weak<F> {
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name: &'static str,
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addr: AtomicUsize,
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_marker: marker::PhantomData<F>,
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}
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impl<F> Weak<F> {
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pub const fn new(name: &'static str) -> Weak<F> {
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Weak { name, addr: AtomicUsize::new(1), _marker: marker::PhantomData }
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}
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pub fn get(&self) -> Option<F> {
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assert_eq!(mem::size_of::<F>(), mem::size_of::<usize>());
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unsafe {
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if self.addr.load(Ordering::SeqCst) == 1 {
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self.addr.store(fetch(self.name), Ordering::SeqCst);
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}
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match self.addr.load(Ordering::SeqCst) {
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0 => None,
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addr => Some(mem::transmute_copy::<usize, F>(&addr)),
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}
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}
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}
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}
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unsafe fn fetch(name: &str) -> usize {
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let name = match CStr::from_bytes_with_nul(name.as_bytes()) {
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Ok(cstr) => cstr,
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Err(..) => return 0,
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};
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assert!(false, "FIXME: fetch");
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libc::dlsym(libc::RTLD_DEFAULT, name.as_ptr()) as usize
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}
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