445 lines
18 KiB
Rust
445 lines
18 KiB
Rust
// A hack for docs.rs to build documentation that has both windows and linux documentation in the
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// same rustdoc build visible.
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#[cfg(all(libloading_docs, not(unix)))]
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mod unix_imports {}
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#[cfg(any(not(libloading_docs), unix))]
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mod unix_imports {
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pub(super) use std::os::unix::ffi::OsStrExt;
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}
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pub use self::consts::*;
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use self::unix_imports::*;
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use std::ffi::{CStr, OsStr};
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use std::os::raw;
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use std::{fmt, marker, mem, ptr};
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use util::{cstr_cow_from_bytes, ensure_compatible_types};
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mod consts;
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// dl* family of functions did not have enough thought put into it.
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//
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// Whole error handling scheme is done via setting and querying some global state, therefore it is
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// not safe to use dynamic library loading in MT-capable environment at all. Only in POSIX 2008+TC1
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// a thread-local state was allowed for `dlerror`, making the dl* family of functions MT-safe.
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//
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// In practice (as of 2020-04-01) most of the widely used targets use a thread-local for error
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// state and have been doing so for a long time. Regardless the comments in this function shall
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// remain as a documentation for the future generations.
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fn with_dlerror<T, F>(wrap: fn(crate::error::DlDescription) -> crate::Error, closure: F)
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-> Result<T, Option<crate::Error>>
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where F: FnOnce() -> Option<T> {
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// We used to guard all uses of dl* functions with our own mutex. This made them safe to use in
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// MT programs provided the only way a program used dl* was via this library. However, it also
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// had a number of downsides or cases where it failed to handle the problems. For instance,
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// if any other library called `dlerror` internally concurrently with `libloading` things would
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// still go awry.
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//
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// On platforms where `dlerror` is still MT-unsafe, `dlsym` (`Library::get`) can spuriously
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// succeed and return a null pointer for a symbol when the actual symbol look-up operation
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// fails. Instances where the actual symbol _could_ be `NULL` are platform specific. For
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// instance on GNU glibc based-systems (an excerpt from dlsym(3)):
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//
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// > The value of a symbol returned by dlsym() will never be NULL if the shared object is the
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// > result of normal compilation, since a global symbol is never placed at the NULL
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// > address. There are nevertheless cases where a lookup using dlsym() may return NULL as the
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// > value of a symbol. For example, the symbol value may be the result of a GNU indirect
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// > function (IFUNC) resolver function that returns NULL as the resolved value.
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// While we could could call `dlerror` here to clear the previous error value, only the `dlsym`
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// call depends on it being cleared beforehand and only in some cases too. We will instead
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// clear the error inside the dlsym binding instead.
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//
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// In all the other cases, clearing the error here will only be hiding misuse of these bindings
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// or a bug in implementation of dl* family of functions.
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closure().ok_or_else(|| unsafe {
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// This code will only get executed if the `closure` returns `None`.
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let error = dlerror();
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if error.is_null() {
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// In non-dlsym case this may happen when there’re bugs in our bindings or there’s
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// non-libloading user of libdl; possibly in another thread.
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None
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} else {
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// You can’t even rely on error string being static here; call to subsequent dlerror
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// may invalidate or overwrite the error message. Why couldn’t they simply give up the
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// ownership over the message?
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// TODO: should do locale-aware conversion here. OTOH Rust doesn’t seem to work well in
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// any system that uses non-utf8 locale, so I doubt there’s a problem here.
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let message = CStr::from_ptr(error).into();
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Some(wrap(crate::error::DlDescription(message)))
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// Since we do a copy of the error string above, maybe we should call dlerror again to
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// let libdl know it may free its copy of the string now?
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}
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})
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}
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/// A platform-specific counterpart of the cross-platform [`Library`](crate::Library).
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pub struct Library {
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handle: *mut raw::c_void
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}
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unsafe impl Send for Library {}
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// That being said... this section in the volume 2 of POSIX.1-2008 states:
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//
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// > All functions defined by this volume of POSIX.1-2008 shall be thread-safe, except that the
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// > following functions need not be thread-safe.
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//
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// With notable absence of any dl* function other than dlerror in the list. By “this volume”
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// I suppose they refer precisely to the “volume 2”. dl* family of functions are specified
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// by this same volume, so the conclusion is indeed that dl* functions are required by POSIX
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// to be thread-safe. Great!
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//
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// See for more details:
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//
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// * https://github.com/nagisa/rust_libloading/pull/17
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// * http://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_09_01
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unsafe impl Sync for Library {}
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impl Library {
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/// Find and eagerly load a shared library (module).
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///
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/// If the `filename` contains a [path separator], the `filename` is interpreted as a `path` to
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/// a file. Otherwise, platform-specific algorithms are employed to find a library with a
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/// matching file name.
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///
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/// This is equivalent to <code>[Library::open](filename, [RTLD_LAZY] | [RTLD_LOCAL])</code>.
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///
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/// [path separator]: std::path::MAIN_SEPARATOR
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///
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/// # Safety
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///
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/// When a library is loaded, initialisation routines contained within the library are executed.
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/// For the purposes of safety, the execution of these routines is conceptually the same calling an
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/// unknown foreign function and may impose arbitrary requirements on the caller for the call
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/// to be sound.
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///
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/// Additionally, the callers of this function must also ensure that execution of the
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/// termination routines contained within the library is safe as well. These routines may be
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/// executed when the library is unloaded.
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#[inline]
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pub unsafe fn new<P: AsRef<OsStr>>(filename: P) -> Result<Library, crate::Error> {
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Library::open(Some(filename), RTLD_LAZY | RTLD_LOCAL)
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}
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/// Load the `Library` representing the current executable.
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///
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/// [`Library::get`] calls of the returned `Library` will look for symbols in following
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/// locations in order:
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///
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/// 1. The original program image;
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/// 2. Any executable object files (e.g. shared libraries) loaded at program startup;
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/// 3. Any executable object files loaded at runtime (e.g. via other `Library::new` calls or via
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/// calls to the `dlopen` function).
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///
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/// Note that the behaviour of a `Library` loaded with this method is different from that of
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/// Libraries loaded with [`os::windows::Library::this`].
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///
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/// This is equivalent to <code>[Library::open](None, [RTLD_LAZY] | [RTLD_LOCAL])</code>.
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///
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/// [`os::windows::Library::this`]: crate::os::windows::Library::this
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#[inline]
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pub fn this() -> Library {
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unsafe {
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// SAFE: this does not load any new shared library images, no danger in it executing
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// initialiser routines.
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Library::open(None::<&OsStr>, RTLD_LAZY | RTLD_LOCAL).expect("this should never fail")
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}
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}
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/// Find and load an executable object file (shared library).
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///
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/// See documentation for [`Library::this`] for further description of the behaviour
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/// when the `filename` is `None`. Otherwise see [`Library::new`].
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///
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/// Corresponds to `dlopen(filename, flags)`.
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///
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/// # Safety
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///
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/// When a library is loaded, initialisation routines contained within the library are executed.
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/// For the purposes of safety, the execution of these routines is conceptually the same calling an
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/// unknown foreign function and may impose arbitrary requirements on the caller for the call
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/// to be sound.
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///
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/// Additionally, the callers of this function must also ensure that execution of the
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/// termination routines contained within the library is safe as well. These routines may be
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/// executed when the library is unloaded.
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pub unsafe fn open<P>(filename: Option<P>, flags: raw::c_int) -> Result<Library, crate::Error>
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where P: AsRef<OsStr> {
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let filename = match filename {
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None => None,
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Some(ref f) => Some(cstr_cow_from_bytes(f.as_ref().as_bytes())?),
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};
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with_dlerror(|desc| crate::Error::DlOpen { desc }, move || {
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let result = dlopen(match filename {
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None => ptr::null(),
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Some(ref f) => f.as_ptr()
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}, flags);
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// ensure filename lives until dlopen completes
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drop(filename);
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if result.is_null() {
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None
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} else {
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Some(Library {
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handle: result
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})
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}
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}).map_err(|e| e.unwrap_or(crate::Error::DlOpenUnknown))
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}
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unsafe fn get_impl<T, F>(&self, symbol: &[u8], on_null: F) -> Result<Symbol<T>, crate::Error>
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where F: FnOnce() -> Result<Symbol<T>, crate::Error>
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{
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ensure_compatible_types::<T, *mut raw::c_void>()?;
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let symbol = cstr_cow_from_bytes(symbol)?;
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// `dlsym` may return nullptr in two cases: when a symbol genuinely points to a null
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// pointer or the symbol cannot be found. In order to detect this case a double dlerror
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// pattern must be used, which is, sadly, a little bit racy.
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//
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// We try to leave as little space as possible for this to occur, but we can’t exactly
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// fully prevent it.
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match with_dlerror(|desc| crate::Error::DlSym { desc }, || {
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dlerror();
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let symbol = dlsym(self.handle, symbol.as_ptr());
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if symbol.is_null() {
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None
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} else {
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Some(Symbol {
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pointer: symbol,
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pd: marker::PhantomData
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})
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}
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}) {
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Err(None) => on_null(),
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Err(Some(e)) => Err(e),
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Ok(x) => Ok(x)
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}
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}
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/// Get a pointer to a function or static variable by symbol name.
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///
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/// The `symbol` may not contain any null bytes, with the exception of the last byte. Providing a
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/// null terminated `symbol` may help to avoid an allocation.
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///
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/// Symbol is interpreted as-is; no mangling is done. This means that symbols like `x::y` are
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/// most likely invalid.
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///
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/// # Safety
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///
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/// Users of this API must specify the correct type of the function or variable loaded. Using a
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/// `Symbol` with a wrong type is undefined.
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///
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/// # Platform-specific behaviour
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///
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/// Implementation of thread local variables is extremely platform specific and uses of such
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/// variables that work on e.g. Linux may have unintended behaviour on other targets.
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///
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/// On POSIX implementations where the `dlerror` function is not confirmed to be MT-safe (such
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/// as FreeBSD), this function will unconditionally return an error when the underlying `dlsym`
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/// call returns a null pointer. There are rare situations where `dlsym` returns a genuine null
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/// pointer without it being an error. If loading a null pointer is something you care about,
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/// consider using the [`Library::get_singlethreaded`] call.
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#[inline(always)]
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pub unsafe fn get<T>(&self, symbol: &[u8]) -> Result<Symbol<T>, crate::Error> {
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extern crate cfg_if;
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cfg_if::cfg_if! {
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// These targets are known to have MT-safe `dlerror`.
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if #[cfg(any(
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target_os = "linux",
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target_os = "android",
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target_os = "openbsd",
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target_os = "macos",
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target_os = "ios",
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target_os = "solaris",
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target_os = "illumos",
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target_os = "redox",
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target_os = "fuchsia"
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))] {
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self.get_singlethreaded(symbol)
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} else {
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self.get_impl(symbol, || Err(crate::Error::DlSymUnknown))
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}
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}
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}
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/// Get a pointer to function or static variable by symbol name.
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///
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/// The `symbol` may not contain any null bytes, with the exception of the last byte. Providing a
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/// null terminated `symbol` may help to avoid an allocation.
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///
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/// Symbol is interpreted as-is; no mangling is done. This means that symbols like `x::y` are
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/// most likely invalid.
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///
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/// # Safety
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///
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/// Users of this API must specify the correct type of the function or variable loaded.
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///
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/// It is up to the user of this library to ensure that no other calls to an MT-unsafe
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/// implementation of `dlerror` occur during the execution of this function. Failing that, the
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/// behaviour of this function is not defined.
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///
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/// # Platform-specific behaviour
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///
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/// The implementation of thread-local variables is extremely platform specific and uses of such
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/// variables that work on e.g. Linux may have unintended behaviour on other targets.
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#[inline(always)]
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pub unsafe fn get_singlethreaded<T>(&self, symbol: &[u8]) -> Result<Symbol<T>, crate::Error> {
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self.get_impl(symbol, || Ok(Symbol {
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pointer: ptr::null_mut(),
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pd: marker::PhantomData
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}))
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}
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/// Convert the `Library` to a raw handle.
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///
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/// The handle returned by this function shall be usable with APIs which accept handles
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/// as returned by `dlopen`.
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pub fn into_raw(self) -> *mut raw::c_void {
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let handle = self.handle;
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mem::forget(self);
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handle
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}
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/// Convert a raw handle returned by `dlopen`-family of calls to a `Library`.
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///
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/// # Safety
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///
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/// The pointer shall be a result of a successful call of the `dlopen`-family of functions or a
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/// pointer previously returned by `Library::into_raw` call. It must be valid to call `dlclose`
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/// with this pointer as an argument.
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pub unsafe fn from_raw(handle: *mut raw::c_void) -> Library {
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Library {
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handle
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}
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}
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/// Unload the library.
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///
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/// This method might be a no-op, depending on the flags with which the `Library` was opened,
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/// what library was opened or other platform specifics.
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///
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/// You only need to call this if you are interested in handling any errors that may arise when
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/// library is unloaded. Otherwise the implementation of `Drop` for `Library` will close the
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/// library and ignore the errors were they arise.
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///
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/// The underlying data structures may still get leaked if an error does occur.
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pub fn close(self) -> Result<(), crate::Error> {
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let result = with_dlerror(|desc| crate::Error::DlClose { desc }, || {
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if unsafe { dlclose(self.handle) } == 0 {
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Some(())
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} else {
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None
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}
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}).map_err(|e| e.unwrap_or(crate::Error::DlCloseUnknown));
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// While the library is not free'd yet in case of an error, there is no reason to try
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// dropping it again, because all that will do is try calling `dlclose` again. only
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// this time it would ignore the return result, which we already seen failing…
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std::mem::forget(self);
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result
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}
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}
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impl Drop for Library {
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fn drop(&mut self) {
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unsafe {
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dlclose(self.handle);
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}
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}
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}
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impl fmt::Debug for Library {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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f.write_str(&format!("Library@{:p}", self.handle))
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}
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}
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/// Symbol from a library.
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///
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/// A major difference compared to the cross-platform `Symbol` is that this does not ensure that the
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/// `Symbol` does not outlive the `Library` it comes from.
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pub struct Symbol<T> {
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pointer: *mut raw::c_void,
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pd: marker::PhantomData<T>
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}
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impl<T> Symbol<T> {
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/// Convert the loaded `Symbol` into a raw pointer.
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pub fn into_raw(self) -> *mut raw::c_void {
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self.pointer
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}
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}
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impl<T> Symbol<Option<T>> {
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/// Lift Option out of the symbol.
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pub fn lift_option(self) -> Option<Symbol<T>> {
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if self.pointer.is_null() {
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None
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} else {
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Some(Symbol {
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pointer: self.pointer,
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pd: marker::PhantomData,
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})
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}
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}
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}
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unsafe impl<T: Send> Send for Symbol<T> {}
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unsafe impl<T: Sync> Sync for Symbol<T> {}
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impl<T> Clone for Symbol<T> {
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fn clone(&self) -> Symbol<T> {
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Symbol { ..*self }
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}
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}
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impl<T> ::std::ops::Deref for Symbol<T> {
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type Target = T;
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fn deref(&self) -> &T {
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unsafe {
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// Additional reference level for a dereference on `deref` return value.
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&*(&self.pointer as *const *mut _ as *const T)
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}
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}
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}
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impl<T> fmt::Debug for Symbol<T> {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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unsafe {
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let mut info = mem::MaybeUninit::<DlInfo>::uninit();
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if dladdr(self.pointer, info.as_mut_ptr()) != 0 {
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let info = info.assume_init();
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if info.dli_sname.is_null() {
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f.write_str(&format!("Symbol@{:p} from {:?}",
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self.pointer,
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CStr::from_ptr(info.dli_fname)))
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} else {
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f.write_str(&format!("Symbol {:?}@{:p} from {:?}",
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CStr::from_ptr(info.dli_sname), self.pointer,
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CStr::from_ptr(info.dli_fname)))
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}
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} else {
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f.write_str(&format!("Symbol@{:p}", self.pointer))
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}
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}
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}
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}
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// Platform specific things
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#[cfg_attr(any(target_os = "linux", target_os = "android"), link(name="dl"))]
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#[cfg_attr(any(target_os = "freebsd", target_os = "dragonfly"), link(name="c"))]
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extern {
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fn dlopen(filename: *const raw::c_char, flags: raw::c_int) -> *mut raw::c_void;
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fn dlclose(handle: *mut raw::c_void) -> raw::c_int;
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fn dlsym(handle: *mut raw::c_void, symbol: *const raw::c_char) -> *mut raw::c_void;
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fn dlerror() -> *mut raw::c_char;
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fn dladdr(addr: *mut raw::c_void, info: *mut DlInfo) -> raw::c_int;
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}
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#[repr(C)]
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struct DlInfo {
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dli_fname: *const raw::c_char,
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dli_fbase: *mut raw::c_void,
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dli_sname: *const raw::c_char,
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dli_saddr: *mut raw::c_void
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}
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