Auto merge of rust-lang#90716 - euclio:libloading, r=cjgillot

replace dynamic library module with libloading

This PR deletes the `rustc_metadata::dynamic_lib` module in favor of the popular and better tested [`libloading` crate](https://github.com/nagisa/rust_libloading/).

We don't benefit from `libloading`'s symbol lifetimes since we end up leaking the loaded library in all cases, but the call-sites look much nicer by improving error handling and abstracting away some transmutes. We also can remove `rustc_metadata`'s direct dependencies on `libc` and `winapi`.

This PR also adds an exception for `libloading` (and its license) to tidy, so this will need sign-off from the compiler team.

Author: bors

Cargo.lock

@@ -1926,6 +1926,16 @@ dependencies = [
  "pkg-config",
 ]
 
+[[package]]
+name = "libloading"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c0cf036d15402bea3c5d4de17b3fce76b3e4a56ebc1f577be0e7a72f7c607cf0"
+dependencies = [
+ "cfg-if 1.0.0",
+ "winapi",
+]
+
 [[package]]
 name = "libm"
 version = "0.1.4"
@@ -3694,6 +3704,7 @@ dependencies = [
  "bitflags",
  "cstr",
  "libc",
+ "libloading",
  "measureme 10.0.0",
  "rustc-demangle",
  "rustc_arena",
@@ -3978,6 +3989,7 @@ name = "rustc_interface"
 version = "0.0.0"
 dependencies = [
  "libc",
+ "libloading",
  "rustc-rayon",
  "rustc-rayon-core",
  "rustc_ast",
@@ -4090,7 +4102,7 @@ dependencies = [
 name = "rustc_metadata"
 version = "0.0.0"
 dependencies = [
- "libc",
+ "libloading",
  "odht",
  "rustc_ast",
  "rustc_attr",
@@ -4110,7 +4122,6 @@ dependencies = [
  "smallvec",
  "snap",
  "tracing",
- "winapi",
 ]
 
 [[package]]
@@ -4283,6 +4294,7 @@ dependencies = [
 name = "rustc_plugin_impl"
 version = "0.0.0"
 dependencies = [
+ "libloading",
  "rustc_ast",
  "rustc_errors",
  "rustc_hir",

compiler/rustc_codegen_llvm/Cargo.toml

@@ -11,6 +11,7 @@ doctest = false
 bitflags = "1.0"
 cstr = "0.2"
 libc = "0.2"
+libloading = "0.7.1"
 measureme = "10.0.0"
 tracing = "0.1"
 rustc_middle = { path = "../rustc_middle" }

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -1,9 +1,9 @@
 use crate::back::write::create_informational_target_machine;
 use crate::{llvm, llvm_util};
 use libc::c_int;
+use libloading::Library;
 use rustc_codegen_ssa::target_features::supported_target_features;
 use rustc_data_structures::fx::FxHashSet;
-use rustc_metadata::dynamic_lib::DynamicLibrary;
 use rustc_middle::bug;
 use rustc_session::config::PrintRequest;
 use rustc_session::Session;
@@ -13,7 +13,6 @@ use std::ffi::{CStr, CString};
 use tracing::debug;
 
 use std::mem;
-use std::path::Path;
 use std::ptr;
 use std::slice;
 use std::str;
@@ -120,14 +119,14 @@ unsafe fn configure_llvm(sess: &Session) {
 
     llvm::LLVMInitializePasses();
 
+    // Register LLVM plugins by loading them into the compiler process.
     for plugin in &sess.opts.debugging_opts.llvm_plugins {
-        let path = Path::new(plugin);
-        let res = DynamicLibrary::open(path);
-        match res {
-            Ok(_) => debug!("LLVM plugin loaded succesfully {} ({})", path.display(), plugin),
-            Err(e) => bug!("couldn't load plugin: {}", e),
-        }
-        mem::forget(res);
+        let lib = Library::new(plugin).unwrap_or_else(|e| bug!("couldn't load plugin: {}", e));
+        debug!("LLVM plugin loaded successfully {:?} ({})", lib, plugin);
+
+        // Intentionally leak the dynamic library. We can't ever unload it
+        // since the library can make things that will live arbitrarily long.
+        mem::forget(lib);
     }
 
     rustc_llvm::initialize_available_targets();

compiler/rustc_interface/Cargo.toml

@@ -8,6 +8,7 @@ doctest = false
 
 [dependencies]
 libc = "0.2"
+libloading = "0.7.1"
 tracing = "0.1"
 rustc-rayon-core = "0.3.1"
 rayon = { version = "0.3.1", package = "rustc-rayon" }

compiler/rustc_interface/src/util.rs

@@ -1,3 +1,4 @@
+use libloading::Library;
 use rustc_ast::mut_visit::{visit_clobber, MutVisitor, *};
 use rustc_ast::ptr::P;
 use rustc_ast::{self as ast, AttrVec, BlockCheckMode};
@@ -7,7 +8,6 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::jobserver;
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::registry::Registry;
-use rustc_metadata::dynamic_lib::DynamicLibrary;
 #[cfg(parallel_compiler)]
 use rustc_middle::ty::tls;
 use rustc_parse::validate_attr;
@@ -39,6 +39,9 @@ use std::sync::{Arc, Mutex};
 use std::thread;
 use tracing::info;
 
+/// Function pointer type that constructs a new CodegenBackend.
+pub type MakeBackendFn = fn() -> Box<dyn CodegenBackend>;
+
 /// Adds `target_feature = "..."` cfgs for a variety of platform
 /// specific features (SSE, NEON etc.).
 ///
@@ -211,28 +214,24 @@ pub fn setup_callbacks_and_run_in_thread_pool_with_globals<F: FnOnce() -> R + Se
     })
 }
 
-fn load_backend_from_dylib(path: &Path) -> fn() -> Box<dyn CodegenBackend> {
-    let lib = DynamicLibrary::open(path).unwrap_or_else(|err| {
-        let err = format!("couldn't load codegen backend {:?}: {:?}", path, err);
+fn load_backend_from_dylib(path: &Path) -> MakeBackendFn {
+    let lib = unsafe { Library::new(path) }.unwrap_or_else(|err| {
+        let err = format!("couldn't load codegen backend {:?}: {}", path, err);
         early_error(ErrorOutputType::default(), &err);
     });
-    unsafe {
-        match lib.symbol("__rustc_codegen_backend") {
-            Ok(f) => {
-                mem::forget(lib);
-                mem::transmute::<*mut u8, _>(f)
-            }
-            Err(e) => {
-                let err = format!(
-                    "couldn't load codegen backend as it \
-                                   doesn't export the `__rustc_codegen_backend` \
-                                   symbol: {:?}",
-                    e
-                );
-                early_error(ErrorOutputType::default(), &err);
-            }
-        }
-    }
+
+    let backend_sym = unsafe { lib.get::<MakeBackendFn>(b"__rustc_codegen_backend") }
+        .unwrap_or_else(|e| {
+            let err = format!("couldn't load codegen backend: {}", e);
+            early_error(ErrorOutputType::default(), &err);
+        });
+
+    // Intentionally leak the dynamic library. We can't ever unload it
+    // since the library can make things that will live arbitrarily long.
+    let backend_sym = unsafe { backend_sym.into_raw() };
+    mem::forget(lib);
+
+    *backend_sym
 }
 
 /// Get the codegen backend based on the name and specified sysroot.
@@ -380,10 +379,7 @@ fn sysroot_candidates() -> Vec<PathBuf> {
     }
 }
 
-pub fn get_codegen_sysroot(
-    maybe_sysroot: &Option<PathBuf>,
-    backend_name: &str,
-) -> fn() -> Box<dyn CodegenBackend> {
+pub fn get_codegen_sysroot(maybe_sysroot: &Option<PathBuf>, backend_name: &str) -> MakeBackendFn {
     // For now we only allow this function to be called once as it'll dlopen a
     // few things, which seems to work best if we only do that once. In
     // general this assertion never trips due to the once guard in `get_codegen_backend`,

compiler/rustc_metadata/Cargo.toml

@@ -7,7 +7,7 @@ edition = "2021"
 doctest = false
 
 [dependencies]
-libc = "0.2"
+libloading = "0.7.1"
 odht = { version = "0.3.1", features = ["nightly"] }
 snap = "1"
 tracing = "0.1"
@@ -27,6 +27,3 @@ rustc_ast = { path = "../rustc_ast" }
 rustc_expand = { path = "../rustc_expand" }
 rustc_span = { path = "../rustc_span" }
 rustc_session = { path = "../rustc_session" }
-
-[target.'cfg(windows)'.dependencies]
-winapi = { version = "0.3", features = ["errhandlingapi", "libloaderapi"] }

compiler/rustc_metadata/src/creader.rs

@@ -1,6 +1,5 @@
 //! Validates all used crates and extern libraries and loads their metadata
 
-use crate::dynamic_lib::DynamicLibrary;
 use crate::locator::{CrateError, CrateLocator, CratePaths};
 use crate::rmeta::{CrateDep, CrateMetadata, CrateNumMap, CrateRoot, MetadataBlob};
 
@@ -676,25 +675,19 @@ impl<'a> CrateLoader<'a> {
     ) -> Result<&'static [ProcMacro], CrateError> {
         // Make sure the path contains a / or the linker will search for it.
         let path = env::current_dir().unwrap().join(path);
-        let lib = match DynamicLibrary::open(&path) {
-            Ok(lib) => lib,
-            Err(s) => return Err(CrateError::DlOpen(s)),
-        };
+        let lib = unsafe { libloading::Library::new(path) }
+            .map_err(|err| CrateError::DlOpen(err.to_string()))?;
 
-        let sym = self.sess.generate_proc_macro_decls_symbol(stable_crate_id);
-        let decls = unsafe {
-            let sym = match lib.symbol(&sym) {
-                Ok(f) => f,
-                Err(s) => return Err(CrateError::DlSym(s)),
-            };
-            *(sym as *const &[ProcMacro])
-        };
+        let sym_name = self.sess.generate_proc_macro_decls_symbol(stable_crate_id);
+        let sym = unsafe { lib.get::<*const &[ProcMacro]>(sym_name.as_bytes()) }
+            .map_err(|err| CrateError::DlSym(err.to_string()))?;
 
         // Intentionally leak the dynamic library. We can't ever unload it
         // since the library can make things that will live arbitrarily long.
+        let sym = unsafe { sym.into_raw() };
         std::mem::forget(lib);
 
-        Ok(decls)
+        Ok(unsafe { **sym })
     }
 
     fn inject_panic_runtime(&mut self, krate: &ast::Crate) {