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