compiler/rustc_codegen_cranelift/src/driver/jit.rs

   1 //! The JIT driver uses [`cranelift_jit`] to JIT execute programs without writing any object
   2 //! files.
   3
   4 use std::cell::RefCell;
   5 use std::ffi::CString;
   6 use std::lazy::SyncOnceCell;
   7 use std::os::raw::{c_char, c_int};
   8 use std::sync::{mpsc, Mutex};
   9
  10 use cranelift_codegen::binemit::{NullStackMapSink, NullTrapSink};
  11 use rustc_codegen_ssa::CrateInfo;
  12 use rustc_middle::mir::mono::MonoItem;
  13 use rustc_session::Session;
  14 use rustc_span::Symbol;
  15
  16 use cranelift_jit::{JITBuilder, JITModule};
  17
  18 use crate::{prelude::*, BackendConfig};
  19 use crate::{CodegenCx, CodegenMode};
  20
  21 struct JitState {
  22     backend_config: BackendConfig,
  23     jit_module: JITModule,
  24 }
  25
  26 thread_local! {
  27     static LAZY_JIT_STATE: RefCell<Option<JitState>> = const { RefCell::new(None) };
  28 }
  29
  30 /// The Sender owned by the rustc thread
  31 static GLOBAL_MESSAGE_SENDER: SyncOnceCell<Mutex<mpsc::Sender<UnsafeMessage>>> =
  32     SyncOnceCell::new();
  33
  34 /// A message that is sent from the jitted runtime to the rustc thread.
  35 /// Senders are responsible for upholding `Send` semantics.
  36 enum UnsafeMessage {
  37     /// Request that the specified `Instance` be lazily jitted.
  38     ///
  39     /// Nothing accessible through `instance_ptr` may be moved or mutated by the sender after
  40     /// this message is sent.
  41     JitFn {
  42         instance_ptr: *const Instance<'static>,
  43         trampoline_ptr: *const u8,
  44         tx: mpsc::Sender<*const u8>,
  45     },
  46 }
  47 unsafe impl Send for UnsafeMessage {}
  48
  49 impl UnsafeMessage {
  50     /// Send the message.
  51     fn send(self) -> Result<(), mpsc::SendError<UnsafeMessage>> {
  52         thread_local! {
  53             /// The Sender owned by the local thread
  54             static LOCAL_MESSAGE_SENDER: mpsc::Sender<UnsafeMessage> =
  55                 GLOBAL_MESSAGE_SENDER
  56                     .get().unwrap()
  57                     .lock().unwrap()
  58                     .clone();
  59         }
  60         LOCAL_MESSAGE_SENDER.with(|sender| sender.send(self))
  61     }
  62 }
  63
  64 fn create_jit_module<'tcx>(
  65     tcx: TyCtxt<'tcx>,
  66     backend_config: &BackendConfig,
  67     hotswap: bool,
  68 ) -> (JITModule, CodegenCx<'tcx>) {
  69     let crate_info = CrateInfo::new(tcx, "dummy_target_cpu".to_string());
  70     let imported_symbols = load_imported_symbols_for_jit(tcx.sess, crate_info);
  71
  72     let isa = crate::build_isa(tcx.sess, backend_config);
  73     let mut jit_builder = JITBuilder::with_isa(isa, cranelift_module::default_libcall_names());
  74     jit_builder.hotswap(hotswap);
  75     crate::compiler_builtins::register_functions_for_jit(&mut jit_builder);
  76     jit_builder.symbols(imported_symbols);
  77     let mut jit_module = JITModule::new(jit_builder);
  78
  79     let mut cx = crate::CodegenCx::new(
  80         tcx,
  81         backend_config.clone(),
  82         jit_module.isa(),
  83         false,
  84         Symbol::intern("dummy_cgu_name"),
  85     );
  86
  87     crate::allocator::codegen(tcx, &mut jit_module, &mut cx.unwind_context);
  88     crate::main_shim::maybe_create_entry_wrapper(
  89         tcx,
  90         &mut jit_module,
  91         &mut cx.unwind_context,
  92         true,
  93         true,
  94     );
  95
  96     (jit_module, cx)
  97 }
  98
  99 pub(crate) fn run_jit(tcx: TyCtxt<'_>, backend_config: BackendConfig) -> ! {
 100     if !tcx.sess.opts.output_types.should_codegen() {
 101         tcx.sess.fatal("JIT mode doesn't work with `cargo check`");
 102     }
 103
 104     if !tcx.sess.crate_types().contains(&rustc_session::config::CrateType::Executable) {
 105         tcx.sess.fatal("can't jit non-executable crate");
 106     }
 107
 108     let (mut jit_module, mut cx) = create_jit_module(
 109         tcx,
 110         &backend_config,
 111         matches!(backend_config.codegen_mode, CodegenMode::JitLazy),
 112     );
 113
 114     let (_, cgus) = tcx.collect_and_partition_mono_items(());
 115     let mono_items = cgus
 116         .iter()
 117         .map(|cgu| cgu.items_in_deterministic_order(tcx).into_iter())
 118         .flatten()
 119         .collect::<FxHashMap<_, (_, _)>>()
 120         .into_iter()
 121         .collect::<Vec<(_, (_, _))>>();
 122
 123     super::time(tcx, backend_config.display_cg_time, "codegen mono items", || {
 124         super::predefine_mono_items(tcx, &mut jit_module, &mono_items);
 125         for (mono_item, _) in mono_items {
 126             match mono_item {
 127                 MonoItem::Fn(inst) => match backend_config.codegen_mode {
 128                     CodegenMode::Aot => unreachable!(),
 129                     CodegenMode::Jit => {
 130                         cx.tcx.sess.time("codegen fn", || {
 131                             crate::base::codegen_fn(&mut cx, &mut jit_module, inst)
 132                         });
 133                     }
 134                     CodegenMode::JitLazy => codegen_shim(&mut cx, &mut jit_module, inst),
 135                 },
 136                 MonoItem::Static(def_id) => {
 137                     crate::constant::codegen_static(tcx, &mut jit_module, def_id);
 138                 }
 139                 MonoItem::GlobalAsm(item_id) => {
 140                     let item = tcx.hir().item(item_id);
 141                     tcx.sess.span_fatal(item.span, "Global asm is not supported in JIT mode");
 142                 }
 143             }
 144         }
 145     });
 146
 147     if !cx.global_asm.is_empty() {
 148         tcx.sess.fatal("Inline asm is not supported in JIT mode");
 149     }
 150
 151     tcx.sess.abort_if_errors();
 152
 153     jit_module.finalize_definitions();
 154     unsafe { cx.unwind_context.register_jit(&jit_module) };
 155
 156     println!(
 157         "Rustc codegen cranelift will JIT run the executable, because -Cllvm-args=mode=jit was passed"
 158     );
 159
 160     let args = std::iter::once(&*tcx.crate_name(LOCAL_CRATE).as_str().to_string())
 161         .chain(backend_config.jit_args.iter().map(|arg| &**arg))
 162         .map(|arg| CString::new(arg).unwrap())
 163         .collect::<Vec<_>>();
 164
 165     let start_sig = Signature {
 166         params: vec![
 167             AbiParam::new(jit_module.target_config().pointer_type()),
 168             AbiParam::new(jit_module.target_config().pointer_type()),
 169         ],
 170         returns: vec![AbiParam::new(jit_module.target_config().pointer_type() /*isize*/)],
 171         call_conv: jit_module.target_config().default_call_conv,
 172     };
 173     let start_func_id = jit_module.declare_function("main", Linkage::Import, &start_sig).unwrap();
 174     let finalized_start: *const u8 = jit_module.get_finalized_function(start_func_id);
 175
 176     LAZY_JIT_STATE.with(|lazy_jit_state| {
 177         let mut lazy_jit_state = lazy_jit_state.borrow_mut();
 178         assert!(lazy_jit_state.is_none());
 179         *lazy_jit_state = Some(JitState { backend_config, jit_module });
 180     });
 181
 182     let f: extern "C" fn(c_int, *const *const c_char) -> c_int =
 183         unsafe { ::std::mem::transmute(finalized_start) };
 184
 185     let (tx, rx) = mpsc::channel();
 186     GLOBAL_MESSAGE_SENDER.set(Mutex::new(tx)).unwrap();
 187
 188     // Spawn the jitted runtime in a new thread so that this rustc thread can handle messages
 189     // (eg to lazily JIT further functions as required)
 190     std::thread::spawn(move || {
 191         let mut argv = args.iter().map(|arg| arg.as_ptr()).collect::<Vec<_>>();
 192
 193         // Push a null pointer as a terminating argument. This is required by POSIX and
 194         // useful as some dynamic linkers use it as a marker to jump over.
 195         argv.push(std::ptr::null());
 196
 197         let ret = f(args.len() as c_int, argv.as_ptr());
 198         std::process::exit(ret);
 199     });
 200
 201     // Handle messages
 202     loop {
 203         match rx.recv().unwrap() {
 204             // lazy JIT compilation request - compile requested instance and return pointer to result
 205             UnsafeMessage::JitFn { instance_ptr, trampoline_ptr, tx } => {
 206                 tx.send(jit_fn(instance_ptr, trampoline_ptr))
 207                     .expect("jitted runtime hung up before response to lazy JIT request was sent");
 208             }
 209         }
 210     }
 211 }
 212
 213 #[no_mangle]
 214 extern "C" fn __clif_jit_fn(
 215     instance_ptr: *const Instance<'static>,
 216     trampoline_ptr: *const u8,
 217 ) -> *const u8 {
 218     // send the JIT request to the rustc thread, with a channel for the response
 219     let (tx, rx) = mpsc::channel();
 220     UnsafeMessage::JitFn { instance_ptr, trampoline_ptr, tx }
 221         .send()
 222         .expect("rustc thread hung up before lazy JIT request was sent");
 223
 224     // block on JIT compilation result
 225     rx.recv().expect("rustc thread hung up before responding to sent lazy JIT request")
 226 }
 227
 228 fn jit_fn(instance_ptr: *const Instance<'static>, trampoline_ptr: *const u8) -> *const u8 {
 229     rustc_middle::ty::tls::with(|tcx| {
 230         // lift is used to ensure the correct lifetime for instance.
 231         let instance = tcx.lift(unsafe { *instance_ptr }).unwrap();
 232
 233         LAZY_JIT_STATE.with(|lazy_jit_state| {
 234             let mut lazy_jit_state = lazy_jit_state.borrow_mut();
 235             let lazy_jit_state = lazy_jit_state.as_mut().unwrap();
 236             let jit_module = &mut lazy_jit_state.jit_module;
 237             let backend_config = lazy_jit_state.backend_config.clone();
 238
 239             let name = tcx.symbol_name(instance).name;
 240             let sig = crate::abi::get_function_sig(tcx, jit_module.isa().triple(), instance);
 241             let func_id = jit_module.declare_function(name, Linkage::Export, &sig).unwrap();
 242
 243             let current_ptr = jit_module.read_got_entry(func_id);
 244
 245             // If the function's GOT entry has already been updated to point at something other
 246             // than the shim trampoline, don't re-jit but just return the new pointer instead.
 247             // This does not need synchronization as this code is executed only by a sole rustc
 248             // thread.
 249             if current_ptr != trampoline_ptr {
 250                 return current_ptr;
 251             }
 252
 253             jit_module.prepare_for_function_redefine(func_id).unwrap();
 254
 255             let mut cx = crate::CodegenCx::new(
 256                 tcx,
 257                 backend_config,
 258                 jit_module.isa(),
 259                 false,
 260                 Symbol::intern("dummy_cgu_name"),
 261             );
 262             tcx.sess.time("codegen fn", || crate::base::codegen_fn(&mut cx, jit_module, instance));
 263
 264             assert!(cx.global_asm.is_empty());
 265             jit_module.finalize_definitions();
 266             unsafe { cx.unwind_context.register_jit(&jit_module) };
 267             jit_module.get_finalized_function(func_id)
 268         })
 269     })
 270 }
 271
 272 fn load_imported_symbols_for_jit(
 273     sess: &Session,
 274     crate_info: CrateInfo,
 275 ) -> Vec<(String, *const u8)> {
 276     use rustc_middle::middle::dependency_format::Linkage;
 277
 278     let mut dylib_paths = Vec::new();
 279
 280     let data = &crate_info
 281         .dependency_formats
 282         .iter()
 283         .find(|(crate_type, _data)| *crate_type == rustc_session::config::CrateType::Executable)
 284         .unwrap()
 285         .1;
 286     for &cnum in &crate_info.used_crates {
 287         let src = &crate_info.used_crate_source[&cnum];
 288         match data[cnum.as_usize() - 1] {
 289             Linkage::NotLinked | Linkage::IncludedFromDylib => {}
 290             Linkage::Static => {
 291                 let name = &crate_info.crate_name[&cnum];
 292                 let mut err = sess.struct_err(&format!("Can't load static lib {}", name.as_str()));
 293                 err.note("rustc_codegen_cranelift can only load dylibs in JIT mode.");
 294                 err.emit();
 295             }
 296             Linkage::Dynamic => {
 297                 dylib_paths.push(src.dylib.as_ref().unwrap().0.clone());
 298             }
 299         }
 300     }
 301
 302     let mut imported_symbols = Vec::new();
 303     for path in dylib_paths {
 304         use object::{Object, ObjectSymbol};
 305         let lib = libloading::Library::new(&path).unwrap();
 306         let obj = std::fs::read(path).unwrap();
 307         let obj = object::File::parse(&*obj).unwrap();
 308         imported_symbols.extend(obj.dynamic_symbols().filter_map(|symbol| {
 309             let name = symbol.name().unwrap().to_string();
 310             if name.is_empty() || !symbol.is_global() || symbol.is_undefined() {
 311                 return None;
 312             }
 313             if name.starts_with("rust_metadata_") {
 314                 // The metadata is part of a section that is not loaded by the dynamic linker in
 315                 // case of cg_llvm.
 316                 return None;
 317             }
 318             let dlsym_name = if cfg!(target_os = "macos") {
 319                 // On macOS `dlsym` expects the name without leading `_`.
 320                 assert!(name.starts_with('_'), "{:?}", name);
 321                 &name[1..]
 322             } else {
 323                 &name
 324             };
 325             let symbol: libloading::Symbol<'_, *const u8> =
 326                 unsafe { lib.get(dlsym_name.as_bytes()) }.unwrap();
 327             Some((name, *symbol))
 328         }));
 329         std::mem::forget(lib)
 330     }
 331
 332     sess.abort_if_errors();
 333
 334     imported_symbols
 335 }
 336
 337 fn codegen_shim<'tcx>(cx: &mut CodegenCx<'tcx>, module: &mut JITModule, inst: Instance<'tcx>) {
 338     let tcx = cx.tcx;
 339
 340     let pointer_type = module.target_config().pointer_type();
 341
 342     let name = tcx.symbol_name(inst).name;
 343     let sig = crate::abi::get_function_sig(tcx, module.isa().triple(), inst);
 344     let func_id = module.declare_function(name, Linkage::Export, &sig).unwrap();
 345
 346     let instance_ptr = Box::into_raw(Box::new(inst));
 347
 348     let jit_fn = module
 349         .declare_function(
 350             "__clif_jit_fn",
 351             Linkage::Import,
 352             &Signature {
 353                 call_conv: module.target_config().default_call_conv,
 354                 params: vec![AbiParam::new(pointer_type), AbiParam::new(pointer_type)],
 355                 returns: vec![AbiParam::new(pointer_type)],
 356             },
 357         )
 358         .unwrap();
 359
 360     cx.cached_context.clear();
 361     let trampoline = &mut cx.cached_context.func;
 362     trampoline.signature = sig.clone();
 363
 364     let mut builder_ctx = FunctionBuilderContext::new();
 365     let mut trampoline_builder = FunctionBuilder::new(trampoline, &mut builder_ctx);
 366
 367     let trampoline_fn = module.declare_func_in_func(func_id, trampoline_builder.func);
 368     let jit_fn = module.declare_func_in_func(jit_fn, trampoline_builder.func);
 369     let sig_ref = trampoline_builder.func.import_signature(sig);
 370
 371     let entry_block = trampoline_builder.create_block();
 372     trampoline_builder.append_block_params_for_function_params(entry_block);
 373     let fn_args = trampoline_builder.func.dfg.block_params(entry_block).to_vec();
 374
 375     trampoline_builder.switch_to_block(entry_block);
 376     let instance_ptr = trampoline_builder.ins().iconst(pointer_type, instance_ptr as u64 as i64);
 377     let trampoline_ptr = trampoline_builder.ins().func_addr(pointer_type, trampoline_fn);
 378     let jitted_fn = trampoline_builder.ins().call(jit_fn, &[instance_ptr, trampoline_ptr]);
 379     let jitted_fn = trampoline_builder.func.dfg.inst_results(jitted_fn)[0];
 380     let call_inst = trampoline_builder.ins().call_indirect(sig_ref, jitted_fn, &fn_args);
 381     let ret_vals = trampoline_builder.func.dfg.inst_results(call_inst).to_vec();
 382     trampoline_builder.ins().return_(&ret_vals);
 383
 384     module
 385         .define_function(
 386             func_id,
 387             &mut cx.cached_context,
 388             &mut NullTrapSink {},
 389             &mut NullStackMapSink {},
 390         )
 391         .unwrap();
 392 }