src/driver/jit.rs

   1 //! The JIT driver uses [`cranelift_simplejit`] to JIT execute programs without writing any object
   2 //! files.
   3
   4 use std::cell::RefCell;
   5 use std::ffi::CString;
   6 use std::os::raw::{c_char, c_int};
   7
   8 use cranelift_codegen::binemit::{NullStackMapSink, NullTrapSink};
   9 use rustc_codegen_ssa::CrateInfo;
  10 use rustc_middle::mir::mono::MonoItem;
  11 use rustc_session::config::EntryFnType;
  12
  13 use cranelift_jit::{JITBuilder, JITModule};
  14
  15 use crate::{prelude::*, BackendConfig};
  16 use crate::{CodegenCx, CodegenMode};
  17
  18 thread_local! {
  19     pub static BACKEND_CONFIG: RefCell<Option<BackendConfig>> = RefCell::new(None);
  20     pub static CURRENT_MODULE: RefCell<Option<JITModule>> = RefCell::new(None);
  21 }
  22
  23 pub(super) fn run_jit(tcx: TyCtxt<'_>, backend_config: BackendConfig) -> ! {
  24     if !tcx.sess.opts.output_types.should_codegen() {
  25         tcx.sess.fatal("JIT mode doesn't work with `cargo check`.");
  26     }
  27
  28     let imported_symbols = load_imported_symbols_for_jit(tcx);
  29
  30     let isa = crate::build_isa(tcx.sess, &backend_config);
  31     let mut jit_builder = JITBuilder::with_isa(isa, cranelift_module::default_libcall_names());
  32     jit_builder.hotswap(matches!(backend_config.codegen_mode, CodegenMode::JitLazy));
  33     crate::compiler_builtins::register_functions_for_jit(&mut jit_builder);
  34     jit_builder.symbols(imported_symbols);
  35     let mut jit_module = JITModule::new(jit_builder);
  36     assert_eq!(pointer_ty(tcx), jit_module.target_config().pointer_type());
  37
  38     let (_, cgus) = tcx.collect_and_partition_mono_items(LOCAL_CRATE);
  39     let mono_items = cgus
  40         .iter()
  41         .map(|cgu| cgu.items_in_deterministic_order(tcx).into_iter())
  42         .flatten()
  43         .collect::<FxHashMap<_, (_, _)>>()
  44         .into_iter()
  45         .collect::<Vec<(_, (_, _))>>();
  46
  47     let mut cx = crate::CodegenCx::new(tcx, backend_config.clone(), &mut jit_module, false);
  48
  49     super::time(tcx, backend_config.display_cg_time, "codegen mono items", || {
  50         super::predefine_mono_items(&mut cx, &mono_items);
  51         for (mono_item, _) in mono_items {
  52             match mono_item {
  53                 MonoItem::Fn(inst) => match backend_config.codegen_mode {
  54                     CodegenMode::Aot => unreachable!(),
  55                     CodegenMode::Jit => {
  56                         cx.tcx.sess.time("codegen fn", || crate::base::codegen_fn(&mut cx, inst));
  57                     }
  58                     CodegenMode::JitLazy => codegen_shim(&mut cx, inst),
  59                 },
  60                 MonoItem::Static(def_id) => {
  61                     crate::constant::codegen_static(&mut cx, def_id);
  62                 }
  63                 MonoItem::GlobalAsm(item_id) => {
  64                     let item = cx.tcx.hir().item(item_id);
  65                     tcx.sess.span_fatal(item.span, "Global asm is not supported in JIT mode");
  66                 }
  67             }
  68         }
  69     });
  70
  71     let (global_asm, _debug, mut unwind_context) =
  72         tcx.sess.time("finalize CodegenCx", || cx.finalize());
  73     jit_module.finalize_definitions();
  74
  75     if !global_asm.is_empty() {
  76         tcx.sess.fatal("Inline asm is not supported in JIT mode");
  77     }
  78
  79     crate::allocator::codegen(tcx, &mut jit_module, &mut unwind_context);
  80
  81     tcx.sess.abort_if_errors();
  82
  83     jit_module.finalize_definitions();
  84     let _unwind_register_guard = unsafe { unwind_context.register_jit(&jit_module) };
  85
  86     println!(
  87         "Rustc codegen cranelift will JIT run the executable, because -Cllvm-args=mode=jit was passed"
  88     );
  89
  90     let args = std::iter::once(&*tcx.crate_name(LOCAL_CRATE).as_str().to_string())
  91         .chain(backend_config.jit_args.iter().map(|arg| &**arg))
  92         .map(|arg| CString::new(arg).unwrap())
  93         .collect::<Vec<_>>();
  94     let mut argv = args.iter().map(|arg| arg.as_ptr()).collect::<Vec<_>>();
  95
  96     // Push a null pointer as a terminating argument. This is required by POSIX and
  97     // useful as some dynamic linkers use it as a marker to jump over.
  98     argv.push(std::ptr::null());
  99
 100     BACKEND_CONFIG.with(|tls_backend_config| {
 101         assert!(tls_backend_config.borrow_mut().replace(backend_config).is_none())
 102     });
 103
 104     let (main_def_id, entry_ty) = tcx.entry_fn(LOCAL_CRATE).unwrap();
 105     let instance = Instance::mono(tcx, main_def_id.to_def_id()).polymorphize(tcx);
 106
 107     match entry_ty {
 108         EntryFnType::Main => {
 109             // FIXME set program arguments somehow
 110
 111             let main_sig = Signature {
 112                 params: vec![],
 113                 returns: vec![],
 114                 call_conv: CallConv::triple_default(&crate::target_triple(tcx.sess)),
 115             };
 116             let main_func_id = jit_module
 117                 .declare_function(tcx.symbol_name(instance).name, Linkage::Import, &main_sig)
 118                 .unwrap();
 119             let finalized_main: *const u8 = jit_module.get_finalized_function(main_func_id);
 120
 121             CURRENT_MODULE.with(|current_module| {
 122                 assert!(current_module.borrow_mut().replace(jit_module).is_none())
 123             });
 124
 125             let f: extern "C" fn() = unsafe { ::std::mem::transmute(finalized_main) };
 126             f();
 127             std::process::exit(0);
 128         }
 129         EntryFnType::Start => {
 130             let start_sig = Signature {
 131                 params: vec![
 132                     AbiParam::new(jit_module.target_config().pointer_type()),
 133                     AbiParam::new(jit_module.target_config().pointer_type()),
 134                 ],
 135                 returns: vec![AbiParam::new(
 136                     jit_module.target_config().pointer_type(), /*isize*/
 137                 )],
 138                 call_conv: CallConv::triple_default(&crate::target_triple(tcx.sess)),
 139             };
 140             let start_func_id = jit_module
 141                 .declare_function(tcx.symbol_name(instance).name, Linkage::Import, &start_sig)
 142                 .unwrap();
 143             let finalized_start: *const u8 = jit_module.get_finalized_function(start_func_id);
 144
 145             CURRENT_MODULE.with(|current_module| {
 146                 assert!(current_module.borrow_mut().replace(jit_module).is_none())
 147             });
 148
 149             let f: extern "C" fn(c_int, *const *const c_char) -> c_int =
 150                 unsafe { ::std::mem::transmute(finalized_start) };
 151             let ret = f(args.len() as c_int, argv.as_ptr());
 152             std::process::exit(ret);
 153         }
 154     }
 155 }
 156
 157 #[no_mangle]
 158 extern "C" fn __clif_jit_fn(instance_ptr: *const Instance<'static>) -> *const u8 {
 159     rustc_middle::ty::tls::with(|tcx| {
 160         // lift is used to ensure the correct lifetime for instance.
 161         let instance = tcx.lift(unsafe { *instance_ptr }).unwrap();
 162
 163         CURRENT_MODULE.with(|jit_module| {
 164             let mut jit_module = jit_module.borrow_mut();
 165             let jit_module = jit_module.as_mut().unwrap();
 166             let backend_config =
 167                 BACKEND_CONFIG.with(|backend_config| backend_config.borrow().clone().unwrap());
 168
 169             let name = tcx.symbol_name(instance).name.to_string();
 170             let sig = crate::abi::get_function_sig(tcx, jit_module.isa().triple(), instance);
 171             let func_id = jit_module.declare_function(&name, Linkage::Export, &sig).unwrap();
 172             jit_module.prepare_for_function_redefine(func_id).unwrap();
 173
 174             let mut cx = crate::CodegenCx::new(tcx, backend_config, jit_module, false);
 175             tcx.sess.time("codegen fn", || crate::base::codegen_fn(&mut cx, instance));
 176
 177             let (global_asm, _debug_context, unwind_context) = cx.finalize();
 178             assert!(global_asm.is_empty());
 179             jit_module.finalize_definitions();
 180             std::mem::forget(unsafe { unwind_context.register_jit(&jit_module) });
 181             jit_module.get_finalized_function(func_id)
 182         })
 183     })
 184 }
 185
 186 fn load_imported_symbols_for_jit(tcx: TyCtxt<'_>) -> Vec<(String, *const u8)> {
 187     use rustc_middle::middle::dependency_format::Linkage;
 188
 189     let mut dylib_paths = Vec::new();
 190
 191     let crate_info = CrateInfo::new(tcx);
 192     let formats = tcx.dependency_formats(LOCAL_CRATE);
 193     let data = &formats
 194         .iter()
 195         .find(|(crate_type, _data)| *crate_type == rustc_session::config::CrateType::Executable)
 196         .unwrap()
 197         .1;
 198     for &(cnum, _) in &crate_info.used_crates_dynamic {
 199         let src = &crate_info.used_crate_source[&cnum];
 200         match data[cnum.as_usize() - 1] {
 201             Linkage::NotLinked | Linkage::IncludedFromDylib => {}
 202             Linkage::Static => {
 203                 let name = tcx.crate_name(cnum);
 204                 let mut err =
 205                     tcx.sess.struct_err(&format!("Can't load static lib {}", name.as_str()));
 206                 err.note("rustc_codegen_cranelift can only load dylibs in JIT mode.");
 207                 err.emit();
 208             }
 209             Linkage::Dynamic => {
 210                 dylib_paths.push(src.dylib.as_ref().unwrap().0.clone());
 211             }
 212         }
 213     }
 214
 215     let mut imported_symbols = Vec::new();
 216     for path in dylib_paths {
 217         use object::{Object, ObjectSymbol};
 218         let lib = libloading::Library::new(&path).unwrap();
 219         let obj = std::fs::read(path).unwrap();
 220         let obj = object::File::parse(&obj).unwrap();
 221         imported_symbols.extend(obj.dynamic_symbols().filter_map(|symbol| {
 222             let name = symbol.name().unwrap().to_string();
 223             if name.is_empty() || !symbol.is_global() || symbol.is_undefined() {
 224                 return None;
 225             }
 226             if name.starts_with("rust_metadata_") {
 227                 // The metadata is part of a section that is not loaded by the dynamic linker in
 228                 // case of cg_llvm.
 229                 return None;
 230             }
 231             let dlsym_name = if cfg!(target_os = "macos") {
 232                 // On macOS `dlsym` expects the name without leading `_`.
 233                 assert!(name.starts_with('_'), "{:?}", name);
 234                 &name[1..]
 235             } else {
 236                 &name
 237             };
 238             let symbol: libloading::Symbol<'_, *const u8> =
 239                 unsafe { lib.get(dlsym_name.as_bytes()) }.unwrap();
 240             Some((name, *symbol))
 241         }));
 242         std::mem::forget(lib)
 243     }
 244
 245     tcx.sess.abort_if_errors();
 246
 247     imported_symbols
 248 }
 249
 250 fn codegen_shim<'tcx>(cx: &mut CodegenCx<'_, 'tcx>, inst: Instance<'tcx>) {
 251     let tcx = cx.tcx;
 252
 253     let pointer_type = cx.module.target_config().pointer_type();
 254
 255     let name = tcx.symbol_name(inst).name.to_string();
 256     let sig = crate::abi::get_function_sig(tcx, cx.module.isa().triple(), inst);
 257     let func_id = cx.module.declare_function(&name, Linkage::Export, &sig).unwrap();
 258
 259     let instance_ptr = Box::into_raw(Box::new(inst));
 260
 261     let jit_fn = cx
 262         .module
 263         .declare_function(
 264             "__clif_jit_fn",
 265             Linkage::Import,
 266             &Signature {
 267                 call_conv: cx.module.target_config().default_call_conv,
 268                 params: vec![AbiParam::new(pointer_type)],
 269                 returns: vec![AbiParam::new(pointer_type)],
 270             },
 271         )
 272         .unwrap();
 273
 274     let mut trampoline = Function::with_name_signature(ExternalName::default(), sig.clone());
 275     let mut builder_ctx = FunctionBuilderContext::new();
 276     let mut trampoline_builder = FunctionBuilder::new(&mut trampoline, &mut builder_ctx);
 277
 278     let jit_fn = cx.module.declare_func_in_func(jit_fn, trampoline_builder.func);
 279     let sig_ref = trampoline_builder.func.import_signature(sig);
 280
 281     let entry_block = trampoline_builder.create_block();
 282     trampoline_builder.append_block_params_for_function_params(entry_block);
 283     let fn_args = trampoline_builder.func.dfg.block_params(entry_block).to_vec();
 284
 285     trampoline_builder.switch_to_block(entry_block);
 286     let instance_ptr = trampoline_builder.ins().iconst(pointer_type, instance_ptr as u64 as i64);
 287     let jitted_fn = trampoline_builder.ins().call(jit_fn, &[instance_ptr]);
 288     let jitted_fn = trampoline_builder.func.dfg.inst_results(jitted_fn)[0];
 289     let call_inst = trampoline_builder.ins().call_indirect(sig_ref, jitted_fn, &fn_args);
 290     let ret_vals = trampoline_builder.func.dfg.inst_results(call_inst).to_vec();
 291     trampoline_builder.ins().return_(&ret_vals);
 292
 293     cx.module
 294         .define_function(
 295             func_id,
 296             &mut Context::for_function(trampoline),
 297             &mut NullTrapSink {},
 298             &mut NullStackMapSink {},
 299         )
 300         .unwrap();
 301 }