compiler/rustc_codegen_cranelift/src/constant.rs

   1 //! Handling of `static`s, `const`s and promoted allocations
   2
   3 use rustc_span::DUMMY_SP;
   4
   5 use rustc_data_structures::fx::FxHashSet;
   6 use rustc_errors::ErrorReported;
   7 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
   8 use rustc_middle::mir::interpret::{
   9     read_target_uint, AllocId, Allocation, ConstValue, ErrorHandled, GlobalAlloc, Pointer, Scalar,
  10 };
  11 use rustc_middle::ty::{Const, ConstKind};
  12
  13 use cranelift_codegen::ir::GlobalValueData;
  14 use cranelift_module::*;
  15
  16 use crate::prelude::*;
  17
  18 #[derive(Default)]
  19 pub(crate) struct ConstantCx {
  20     todo: Vec<TodoItem>,
  21     done: FxHashSet<DataId>,
  22 }
  23
  24 #[derive(Copy, Clone, Debug)]
  25 enum TodoItem {
  26     Alloc(AllocId),
  27     Static(DefId),
  28 }
  29
  30 impl ConstantCx {
  31     pub(crate) fn finalize(mut self, tcx: TyCtxt<'_>, module: &mut impl Module) {
  32         //println!("todo {:?}", self.todo);
  33         define_all_allocs(tcx, module, &mut self);
  34         //println!("done {:?}", self.done);
  35         self.done.clear();
  36     }
  37 }
  38
  39 pub(crate) fn check_constants(fx: &mut FunctionCx<'_, '_, impl Module>) {
  40     for constant in &fx.mir.required_consts {
  41         let const_ = fx.monomorphize(&constant.literal);
  42         match const_.val {
  43             ConstKind::Value(_) => {}
  44             ConstKind::Unevaluated(def, ref substs, promoted) => {
  45                 if let Err(err) =
  46                     fx.tcx
  47                         .const_eval_resolve(ParamEnv::reveal_all(), def, substs, promoted, None)
  48                 {
  49                     match err {
  50                         ErrorHandled::Reported(ErrorReported) | ErrorHandled::Linted => {
  51                             fx.tcx
  52                                 .sess
  53                                 .span_err(constant.span, "erroneous constant encountered");
  54                         }
  55                         ErrorHandled::TooGeneric => {
  56                             span_bug!(
  57                                 constant.span,
  58                                 "codgen encountered polymorphic constant: {:?}",
  59                                 err
  60                             );
  61                         }
  62                     }
  63                 }
  64             }
  65             ConstKind::Param(_)
  66             | ConstKind::Infer(_)
  67             | ConstKind::Bound(_, _)
  68             | ConstKind::Placeholder(_)
  69             | ConstKind::Error(_) => unreachable!("{:?}", const_),
  70         }
  71     }
  72 }
  73
  74 pub(crate) fn codegen_static(constants_cx: &mut ConstantCx, def_id: DefId) {
  75     constants_cx.todo.push(TodoItem::Static(def_id));
  76 }
  77
  78 pub(crate) fn codegen_tls_ref<'tcx>(
  79     fx: &mut FunctionCx<'_, 'tcx, impl Module>,
  80     def_id: DefId,
  81     layout: TyAndLayout<'tcx>,
  82 ) -> CValue<'tcx> {
  83     let data_id = data_id_for_static(fx.tcx, &mut fx.cx.module, def_id, false);
  84     let local_data_id = fx.cx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
  85     #[cfg(debug_assertions)]
  86     fx.add_comment(local_data_id, format!("tls {:?}", def_id));
  87     let tls_ptr = fx.bcx.ins().tls_value(fx.pointer_type, local_data_id);
  88     CValue::by_val(tls_ptr, layout)
  89 }
  90
  91 fn codegen_static_ref<'tcx>(
  92     fx: &mut FunctionCx<'_, 'tcx, impl Module>,
  93     def_id: DefId,
  94     layout: TyAndLayout<'tcx>,
  95 ) -> CPlace<'tcx> {
  96     let data_id = data_id_for_static(fx.tcx, &mut fx.cx.module, def_id, false);
  97     let local_data_id = fx.cx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
  98     #[cfg(debug_assertions)]
  99     fx.add_comment(local_data_id, format!("{:?}", def_id));
 100     let global_ptr = fx.bcx.ins().global_value(fx.pointer_type, local_data_id);
 101     assert!(!layout.is_unsized(), "unsized statics aren't supported");
 102     assert!(
 103         matches!(fx.bcx.func.global_values[local_data_id], GlobalValueData::Symbol { tls: false, ..}),
 104         "tls static referenced without Rvalue::ThreadLocalRef"
 105     );
 106     CPlace::for_ptr(crate::pointer::Pointer::new(global_ptr), layout)
 107 }
 108
 109 pub(crate) fn codegen_constant<'tcx>(
 110     fx: &mut FunctionCx<'_, 'tcx, impl Module>,
 111     constant: &Constant<'tcx>,
 112 ) -> CValue<'tcx> {
 113     let const_ = fx.monomorphize(&constant.literal);
 114     let const_val = match const_.val {
 115         ConstKind::Value(const_val) => const_val,
 116         ConstKind::Unevaluated(def, ref substs, promoted) if fx.tcx.is_static(def.did) => {
 117             assert!(substs.is_empty());
 118             assert!(promoted.is_none());
 119
 120             return codegen_static_ref(
 121                 fx,
 122                 def.did,
 123                 fx.layout_of(fx.monomorphize(&constant.literal.ty)),
 124             )
 125             .to_cvalue(fx);
 126         }
 127         ConstKind::Unevaluated(def, ref substs, promoted) => {
 128             match fx
 129                 .tcx
 130                 .const_eval_resolve(ParamEnv::reveal_all(), def, substs, promoted, None)
 131             {
 132                 Ok(const_val) => const_val,
 133                 Err(_) => {
 134                     if promoted.is_none() {
 135                         fx.tcx
 136                             .sess
 137                             .span_err(constant.span, "erroneous constant encountered");
 138                     }
 139                     return crate::trap::trap_unreachable_ret_value(
 140                         fx,
 141                         fx.layout_of(const_.ty),
 142                         "erroneous constant encountered",
 143                     );
 144                 }
 145             }
 146         }
 147         ConstKind::Param(_)
 148         | ConstKind::Infer(_)
 149         | ConstKind::Bound(_, _)
 150         | ConstKind::Placeholder(_)
 151         | ConstKind::Error(_) => unreachable!("{:?}", const_),
 152     };
 153
 154     codegen_const_value(fx, const_val, const_.ty)
 155 }
 156
 157 pub(crate) fn codegen_const_value<'tcx>(
 158     fx: &mut FunctionCx<'_, 'tcx, impl Module>,
 159     const_val: ConstValue<'tcx>,
 160     ty: Ty<'tcx>,
 161 ) -> CValue<'tcx> {
 162     let layout = fx.layout_of(ty);
 163     assert!(!layout.is_unsized(), "sized const value");
 164
 165     if layout.is_zst() {
 166         return CValue::by_ref(
 167             crate::Pointer::dangling(layout.align.pref),
 168             layout,
 169         );
 170     }
 171
 172     match const_val {
 173         ConstValue::Scalar(x) => {
 174             if fx.clif_type(layout.ty).is_none() {
 175                 let (size, align) = (layout.size, layout.align.pref);
 176                 let mut alloc = Allocation::from_bytes(
 177                     std::iter::repeat(0)
 178                         .take(size.bytes_usize())
 179                         .collect::<Vec<u8>>(),
 180                     align,
 181                 );
 182                 let ptr = Pointer::new(AllocId(!0), Size::ZERO); // The alloc id is never used
 183                 alloc.write_scalar(fx, ptr, x.into(), size).unwrap();
 184                 let alloc = fx.tcx.intern_const_alloc(alloc);
 185                 return CValue::by_ref(pointer_for_allocation(fx, alloc), layout);
 186             }
 187
 188             match x {
 189                 Scalar::Int(int) => {
 190                     CValue::const_val(fx, layout, int)
 191                 }
 192                 Scalar::Ptr(ptr) => {
 193                     let alloc_kind = fx.tcx.get_global_alloc(ptr.alloc_id);
 194                     let base_addr = match alloc_kind {
 195                         Some(GlobalAlloc::Memory(alloc)) => {
 196                             fx.cx.constants_cx.todo.push(TodoItem::Alloc(ptr.alloc_id));
 197                             let data_id = data_id_for_alloc_id(
 198                                 &mut fx.cx.module,
 199                                 ptr.alloc_id,
 200                                 alloc.mutability,
 201                             );
 202                             let local_data_id =
 203                                 fx.cx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
 204                             #[cfg(debug_assertions)]
 205                             fx.add_comment(local_data_id, format!("{:?}", ptr.alloc_id));
 206                             fx.bcx.ins().global_value(fx.pointer_type, local_data_id)
 207                         }
 208                         Some(GlobalAlloc::Function(instance)) => {
 209                             let func_id =
 210                                 crate::abi::import_function(fx.tcx, &mut fx.cx.module, instance);
 211                             let local_func_id =
 212                                 fx.cx.module.declare_func_in_func(func_id, &mut fx.bcx.func);
 213                             fx.bcx.ins().func_addr(fx.pointer_type, local_func_id)
 214                         }
 215                         Some(GlobalAlloc::Static(def_id)) => {
 216                             assert!(fx.tcx.is_static(def_id));
 217                             let data_id =
 218                                 data_id_for_static(fx.tcx, &mut fx.cx.module, def_id, false);
 219                             let local_data_id =
 220                                 fx.cx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
 221                             #[cfg(debug_assertions)]
 222                             fx.add_comment(local_data_id, format!("{:?}", def_id));
 223                             fx.bcx.ins().global_value(fx.pointer_type, local_data_id)
 224                         }
 225                         None => bug!("missing allocation {:?}", ptr.alloc_id),
 226                     };
 227                     let val = if ptr.offset.bytes() != 0 {
 228                         fx.bcx
 229                             .ins()
 230                             .iadd_imm(base_addr, i64::try_from(ptr.offset.bytes()).unwrap())
 231                     } else {
 232                         base_addr
 233                     };
 234                     CValue::by_val(val, layout)
 235                 }
 236             }
 237         }
 238         ConstValue::ByRef { alloc, offset } => CValue::by_ref(
 239             pointer_for_allocation(fx, alloc)
 240                 .offset_i64(fx, i64::try_from(offset.bytes()).unwrap()),
 241             layout,
 242         ),
 243         ConstValue::Slice { data, start, end } => {
 244             let ptr = pointer_for_allocation(fx, data)
 245                 .offset_i64(fx, i64::try_from(start).unwrap())
 246                 .get_addr(fx);
 247             let len = fx.bcx.ins().iconst(
 248                 fx.pointer_type,
 249                 i64::try_from(end.checked_sub(start).unwrap()).unwrap(),
 250             );
 251             CValue::by_val_pair(ptr, len, layout)
 252         }
 253     }
 254 }
 255
 256 fn pointer_for_allocation<'tcx>(
 257     fx: &mut FunctionCx<'_, 'tcx, impl Module>,
 258     alloc: &'tcx Allocation,
 259 ) -> crate::pointer::Pointer {
 260     let alloc_id = fx.tcx.create_memory_alloc(alloc);
 261     fx.cx.constants_cx.todo.push(TodoItem::Alloc(alloc_id));
 262     let data_id = data_id_for_alloc_id(&mut fx.cx.module, alloc_id, alloc.mutability);
 263
 264     let local_data_id = fx.cx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
 265     #[cfg(debug_assertions)]
 266     fx.add_comment(local_data_id, format!("{:?}", alloc_id));
 267     let global_ptr = fx.bcx.ins().global_value(fx.pointer_type, local_data_id);
 268     crate::pointer::Pointer::new(global_ptr)
 269 }
 270
 271 fn data_id_for_alloc_id(
 272     module: &mut impl Module,
 273     alloc_id: AllocId,
 274     mutability: rustc_hir::Mutability,
 275 ) -> DataId {
 276     module
 277         .declare_data(
 278             &format!(".L__alloc_{:x}", alloc_id.0),
 279             Linkage::Local,
 280             mutability == rustc_hir::Mutability::Mut,
 281             false,
 282         )
 283         .unwrap()
 284 }
 285
 286 fn data_id_for_static(
 287     tcx: TyCtxt<'_>,
 288     module: &mut impl Module,
 289     def_id: DefId,
 290     definition: bool,
 291 ) -> DataId {
 292     let rlinkage = tcx.codegen_fn_attrs(def_id).linkage;
 293     let linkage = if definition {
 294         crate::linkage::get_static_linkage(tcx, def_id)
 295     } else if rlinkage == Some(rustc_middle::mir::mono::Linkage::ExternalWeak)
 296         || rlinkage == Some(rustc_middle::mir::mono::Linkage::WeakAny)
 297     {
 298         Linkage::Preemptible
 299     } else {
 300         Linkage::Import
 301     };
 302
 303     let instance = Instance::mono(tcx, def_id).polymorphize(tcx);
 304     let symbol_name = tcx.symbol_name(instance).name;
 305     let ty = instance.ty(tcx, ParamEnv::reveal_all());
 306     let is_mutable = if tcx.is_mutable_static(def_id) {
 307         true
 308     } else {
 309         !ty.is_freeze(tcx.at(DUMMY_SP), ParamEnv::reveal_all())
 310     };
 311     let align = tcx
 312         .layout_of(ParamEnv::reveal_all().and(ty))
 313         .unwrap()
 314         .align
 315         .pref
 316         .bytes();
 317
 318     let attrs = tcx.codegen_fn_attrs(def_id);
 319
 320     let data_id = module
 321         .declare_data(
 322             &*symbol_name,
 323             linkage,
 324             is_mutable,
 325             attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL),
 326         )
 327         .unwrap();
 328
 329     if rlinkage.is_some() {
 330         // Comment copied from https://github.com/rust-lang/rust/blob/45060c2a66dfd667f88bd8b94261b28a58d85bd5/src/librustc_codegen_llvm/consts.rs#L141
 331         // Declare an internal global `extern_with_linkage_foo` which
 332         // is initialized with the address of `foo`.  If `foo` is
 333         // discarded during linking (for example, if `foo` has weak
 334         // linkage and there are no definitions), then
 335         // `extern_with_linkage_foo` will instead be initialized to
 336         // zero.
 337
 338         let ref_name = format!("_rust_extern_with_linkage_{}", symbol_name);
 339         let ref_data_id = module
 340             .declare_data(&ref_name, Linkage::Local, false, false)
 341             .unwrap();
 342         let mut data_ctx = DataContext::new();
 343         data_ctx.set_align(align);
 344         let data = module.declare_data_in_data(data_id, &mut data_ctx);
 345         data_ctx.define(
 346             std::iter::repeat(0)
 347                 .take(pointer_ty(tcx).bytes() as usize)
 348                 .collect(),
 349         );
 350         data_ctx.write_data_addr(0, data, 0);
 351         match module.define_data(ref_data_id, &data_ctx) {
 352             // Every time the static is referenced there will be another definition of this global,
 353             // so duplicate definitions are expected and allowed.
 354             Err(ModuleError::DuplicateDefinition(_)) => {}
 355             res => res.unwrap(),
 356         }
 357         ref_data_id
 358     } else {
 359         data_id
 360     }
 361 }
 362
 363 fn define_all_allocs(tcx: TyCtxt<'_>, module: &mut impl Module, cx: &mut ConstantCx) {
 364     while let Some(todo_item) = cx.todo.pop() {
 365         let (data_id, alloc, section_name) = match todo_item {
 366             TodoItem::Alloc(alloc_id) => {
 367                 //println!("alloc_id {}", alloc_id);
 368                 let alloc = match tcx.get_global_alloc(alloc_id).unwrap() {
 369                     GlobalAlloc::Memory(alloc) => alloc,
 370                     GlobalAlloc::Function(_) | GlobalAlloc::Static(_) => unreachable!(),
 371                 };
 372                 let data_id = data_id_for_alloc_id(module, alloc_id, alloc.mutability);
 373                 (data_id, alloc, None)
 374             }
 375             TodoItem::Static(def_id) => {
 376                 //println!("static {:?}", def_id);
 377
 378                 let section_name = tcx
 379                     .codegen_fn_attrs(def_id)
 380                     .link_section
 381                     .map(|s| s.as_str());
 382
 383                 let alloc = tcx.eval_static_initializer(def_id).unwrap();
 384
 385                 let data_id = data_id_for_static(tcx, module, def_id, true);
 386                 (data_id, alloc, section_name)
 387             }
 388         };
 389
 390         //("data_id {}", data_id);
 391         if cx.done.contains(&data_id) {
 392             continue;
 393         }
 394
 395         let mut data_ctx = DataContext::new();
 396         data_ctx.set_align(alloc.align.bytes());
 397
 398         if let Some(section_name) = section_name {
 399             // FIXME set correct segment for Mach-O files
 400             data_ctx.set_segment_section("", &*section_name);
 401         }
 402
 403         let bytes = alloc
 404             .inspect_with_uninit_and_ptr_outside_interpreter(0..alloc.len())
 405             .to_vec();
 406         data_ctx.define(bytes.into_boxed_slice());
 407
 408         for &(offset, (_tag, reloc)) in alloc.relocations().iter() {
 409             let addend = {
 410                 let endianness = tcx.data_layout.endian;
 411                 let offset = offset.bytes() as usize;
 412                 let ptr_size = tcx.data_layout.pointer_size;
 413                 let bytes = &alloc.inspect_with_uninit_and_ptr_outside_interpreter(
 414                     offset..offset + ptr_size.bytes() as usize,
 415                 );
 416                 read_target_uint(endianness, bytes).unwrap()
 417             };
 418
 419             let reloc_target_alloc = tcx.get_global_alloc(reloc).unwrap();
 420             let data_id = match reloc_target_alloc {
 421                 GlobalAlloc::Function(instance) => {
 422                     assert_eq!(addend, 0);
 423                     let func_id = crate::abi::import_function(tcx, module, instance);
 424                     let local_func_id = module.declare_func_in_data(func_id, &mut data_ctx);
 425                     data_ctx.write_function_addr(offset.bytes() as u32, local_func_id);
 426                     continue;
 427                 }
 428                 GlobalAlloc::Memory(target_alloc) => {
 429                     cx.todo.push(TodoItem::Alloc(reloc));
 430                     data_id_for_alloc_id(module, reloc, target_alloc.mutability)
 431                 }
 432                 GlobalAlloc::Static(def_id) => {
 433                     if tcx
 434                         .codegen_fn_attrs(def_id)
 435                         .flags
 436                         .contains(CodegenFnAttrFlags::THREAD_LOCAL)
 437                     {
 438                         tcx.sess.fatal(&format!(
 439                             "Allocation {:?} contains reference to TLS value {:?}",
 440                             alloc, def_id
 441                         ));
 442                     }
 443
 444                     // Don't push a `TodoItem::Static` here, as it will cause statics used by
 445                     // multiple crates to be duplicated between them. It isn't necessary anyway,
 446                     // as it will get pushed by `codegen_static` when necessary.
 447                     data_id_for_static(tcx, module, def_id, false)
 448                 }
 449             };
 450
 451             let global_value = module.declare_data_in_data(data_id, &mut data_ctx);
 452             data_ctx.write_data_addr(offset.bytes() as u32, global_value, addend as i64);
 453         }
 454
 455         module.define_data(data_id, &data_ctx).unwrap();
 456         cx.done.insert(data_id);
 457     }
 458
 459     assert!(cx.todo.is_empty(), "{:?}", cx.todo);
 460 }
 461
 462 pub(crate) fn mir_operand_get_const_val<'tcx>(
 463     fx: &FunctionCx<'_, 'tcx, impl Module>,
 464     operand: &Operand<'tcx>,
 465 ) -> Option<&'tcx Const<'tcx>> {
 466     match operand {
 467         Operand::Copy(_) | Operand::Move(_) => None,
 468         Operand::Constant(const_) => Some(
 469             fx.monomorphize(&const_.literal)
 470                 .eval(fx.tcx, ParamEnv::reveal_all()),
 471         ),
 472     }
 473 }