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