src/shims/foreign_items.rs

   1 use std::{
   2     convert::{TryFrom, TryInto},
   3     iter,
   4 };
   5
   6 use log::trace;
   7
   8 use rustc_apfloat::Float;
   9 use rustc_ast::expand::allocator::AllocatorKind;
  10 use rustc_hir::{
  11     def::DefKind,
  12     def_id::{CrateNum, DefId, LOCAL_CRATE},
  13 };
  14 use rustc_middle::middle::{
  15     codegen_fn_attrs::CodegenFnAttrFlags, dependency_format::Linkage,
  16     exported_symbols::ExportedSymbol,
  17 };
  18 use rustc_middle::mir;
  19 use rustc_middle::ty;
  20 use rustc_session::config::CrateType;
  21 use rustc_span::{symbol::sym, Symbol};
  22 use rustc_target::{
  23     abi::{Align, Size},
  24     spec::abi::Abi,
  25 };
  26
  27 use super::backtrace::EvalContextExt as _;
  28 use crate::*;
  29
  30 /// Returned by `emulate_foreign_item_by_name`.
  31 pub enum EmulateByNameResult<'mir, 'tcx> {
  32     /// The caller is expected to jump to the return block.
  33     NeedsJumping,
  34     /// Jumping has already been taken care of.
  35     AlreadyJumped,
  36     /// A MIR body has been found for the function
  37     MirBody(&'mir mir::Body<'tcx>),
  38     /// The item is not supported.
  39     NotSupported,
  40 }
  41
  42 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
  43 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
  44     /// Returns the minimum alignment for the target architecture for allocations of the given size.
  45     fn min_align(&self, size: u64, kind: MiriMemoryKind) -> Align {
  46         let this = self.eval_context_ref();
  47         // List taken from `libstd/sys_common/alloc.rs`.
  48         let min_align = match this.tcx.sess.target.arch.as_str() {
  49             "x86" | "arm" | "mips" | "powerpc" | "powerpc64" | "asmjs" | "wasm32" => 8,
  50             "x86_64" | "aarch64" | "mips64" | "s390x" | "sparc64" => 16,
  51             arch => bug!("Unsupported target architecture: {}", arch),
  52         };
  53         // Windows always aligns, even small allocations.
  54         // Source: <https://support.microsoft.com/en-us/help/286470/how-to-use-pageheap-exe-in-windows-xp-windows-2000-and-windows-server>
  55         // But jemalloc does not, so for the C heap we only align if the allocation is sufficiently big.
  56         if kind == MiriMemoryKind::WinHeap || size >= min_align {
  57             return Align::from_bytes(min_align).unwrap();
  58         }
  59         // We have `size < min_align`. Round `size` *down* to the next power of two and use that.
  60         fn prev_power_of_two(x: u64) -> u64 {
  61             let next_pow2 = x.next_power_of_two();
  62             if next_pow2 == x {
  63                 // x *is* a power of two, just use that.
  64                 x
  65             } else {
  66                 // x is between two powers, so next = 2*prev.
  67                 next_pow2 / 2
  68             }
  69         }
  70         Align::from_bytes(prev_power_of_two(size)).unwrap()
  71     }
  72
  73     fn malloc(
  74         &mut self,
  75         size: u64,
  76         zero_init: bool,
  77         kind: MiriMemoryKind,
  78     ) -> InterpResult<'tcx, Pointer<Option<Tag>>> {
  79         let this = self.eval_context_mut();
  80         if size == 0 {
  81             Ok(Pointer::null())
  82         } else {
  83             let align = this.min_align(size, kind);
  84             let ptr = this.memory.allocate(Size::from_bytes(size), align, kind.into())?;
  85             if zero_init {
  86                 // We just allocated this, the access is definitely in-bounds.
  87                 this.memory.write_bytes(ptr.into(), iter::repeat(0u8).take(size as usize)).unwrap();
  88             }
  89             Ok(ptr.into())
  90         }
  91     }
  92
  93     fn free(&mut self, ptr: Pointer<Option<Tag>>, kind: MiriMemoryKind) -> InterpResult<'tcx> {
  94         let this = self.eval_context_mut();
  95         if !this.ptr_is_null(ptr)? {
  96             this.memory.deallocate(ptr, None, kind.into())?;
  97         }
  98         Ok(())
  99     }
 100
 101     fn realloc(
 102         &mut self,
 103         old_ptr: Pointer<Option<Tag>>,
 104         new_size: u64,
 105         kind: MiriMemoryKind,
 106     ) -> InterpResult<'tcx, Pointer<Option<Tag>>> {
 107         let this = self.eval_context_mut();
 108         let new_align = this.min_align(new_size, kind);
 109         if this.ptr_is_null(old_ptr)? {
 110             if new_size == 0 {
 111                 Ok(Pointer::null())
 112             } else {
 113                 let new_ptr =
 114                     this.memory.allocate(Size::from_bytes(new_size), new_align, kind.into())?;
 115                 Ok(new_ptr.into())
 116             }
 117         } else {
 118             if new_size == 0 {
 119                 this.memory.deallocate(old_ptr, None, kind.into())?;
 120                 Ok(Pointer::null())
 121             } else {
 122                 let new_ptr = this.memory.reallocate(
 123                     old_ptr,
 124                     None,
 125                     Size::from_bytes(new_size),
 126                     new_align,
 127                     kind.into(),
 128                 )?;
 129                 Ok(new_ptr.into())
 130             }
 131         }
 132     }
 133
 134     /// Lookup the body of a function that has `link_name` as the symbol name.
 135     fn lookup_exported_symbol(
 136         &mut self,
 137         link_name: Symbol,
 138     ) -> InterpResult<'tcx, Option<&'mir mir::Body<'tcx>>> {
 139         let this = self.eval_context_mut();
 140         let tcx = this.tcx.tcx;
 141
 142         // If the result was cached, just return it.
 143         if let Some(instance) = this.machine.exported_symbols_cache.get(&link_name) {
 144             return instance.map(|instance| this.load_mir(instance.def, None)).transpose();
 145         }
 146
 147         // Find it if it was not cached.
 148         let mut instance_and_crate: Option<(ty::Instance<'_>, CrateNum)> = None;
 149         // `dependency_formats` includes all the transitive informations needed to link a crate,
 150         // which is what we need here since we need to dig out `exported_symbols` from all transitive
 151         // dependencies.
 152         let dependency_formats = tcx.dependency_formats(());
 153         let dependency_format = dependency_formats
 154             .iter()
 155             .find(|(crate_type, _)| *crate_type == CrateType::Executable)
 156             .expect("interpreting a non-executable crate");
 157         for cnum in
 158             iter::once(LOCAL_CRATE).chain(dependency_format.1.iter().enumerate().filter_map(
 159                 |(num, &linkage)| (linkage != Linkage::NotLinked).then_some(CrateNum::new(num + 1)),
 160             ))
 161         {
 162             // We can ignore `_export_level` here: we are a Rust crate, and everything is exported
 163             // from a Rust crate.
 164             for &(symbol, _export_level) in tcx.exported_symbols(cnum) {
 165                 if let ExportedSymbol::NonGeneric(def_id) = symbol {
 166                     let attrs = tcx.codegen_fn_attrs(def_id);
 167                     let symbol_name = if let Some(export_name) = attrs.export_name {
 168                         export_name
 169                     } else if attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE) {
 170                         tcx.item_name(def_id)
 171                     } else {
 172                         // Skip over items without an explicitly defined symbol name.
 173                         continue;
 174                     };
 175                     if symbol_name == link_name {
 176                         if let Some((original_instance, original_cnum)) = instance_and_crate {
 177                             // Make sure we are consistent wrt what is 'first' and 'second'.
 178                             let original_span = tcx.def_span(original_instance.def_id()).data();
 179                             let span =  tcx.def_span(def_id).data();
 180                             if original_span < span {
 181                                 throw_machine_stop!(TerminationInfo::MultipleSymbolDefinitions {
 182                                     link_name,
 183                                     first: original_span,
 184                                     first_crate: tcx.crate_name(original_cnum),
 185                                     second: span,
 186                                     second_crate: tcx.crate_name(cnum),
 187                                 });
 188                             } else {
 189                                 throw_machine_stop!(TerminationInfo::MultipleSymbolDefinitions {
 190                                     link_name,
 191                                     first: span,
 192                                     first_crate: tcx.crate_name(cnum),
 193                                     second: original_span,
 194                                     second_crate: tcx.crate_name(original_cnum),
 195                                 });
 196                             }
 197                         }
 198                         if !matches!(tcx.def_kind(def_id), DefKind::Fn | DefKind::AssocFn) {
 199                             throw_ub_format!(
 200                                 "attempt to call an exported symbol that is not defined as a function"
 201                             );
 202                         }
 203                         instance_and_crate = Some((ty::Instance::mono(tcx, def_id), cnum));
 204                     }
 205                 }
 206             }
 207         }
 208
 209         let instance = instance_and_crate.map(|ic| ic.0);
 210         // Cache it and load its MIR, if found.
 211         this.machine.exported_symbols_cache.try_insert(link_name, instance).unwrap();
 212         instance.map(|instance| this.load_mir(instance.def, None)).transpose()
 213     }
 214
 215     /// Emulates calling a foreign item, failing if the item is not supported.
 216     /// This function will handle `goto_block` if needed.
 217     /// Returns Ok(None) if the foreign item was completely handled
 218     /// by this function.
 219     /// Returns Ok(Some(body)) if processing the foreign item
 220     /// is delegated to another function.
 221     fn emulate_foreign_item(
 222         &mut self,
 223         def_id: DefId,
 224         abi: Abi,
 225         args: &[OpTy<'tcx, Tag>],
 226         ret: Option<(&PlaceTy<'tcx, Tag>, mir::BasicBlock)>,
 227         unwind: StackPopUnwind,
 228     ) -> InterpResult<'tcx, Option<&'mir mir::Body<'tcx>>> {
 229         let this = self.eval_context_mut();
 230         let attrs = this.tcx.get_attrs(def_id);
 231         let link_name = this
 232             .tcx
 233             .sess
 234             .first_attr_value_str_by_name(&attrs, sym::link_name)
 235             .unwrap_or_else(|| this.tcx.item_name(def_id));
 236         let tcx = this.tcx.tcx;
 237
 238         // First: functions that diverge.
 239         let (dest, ret) = match ret {
 240             None =>
 241                 match &*link_name.as_str() {
 242                     "miri_start_panic" => {
 243                         // `check_shim` happens inside `handle_miri_start_panic`.
 244                         this.handle_miri_start_panic(abi, link_name, args, unwind)?;
 245                         return Ok(None);
 246                     }
 247                     // This matches calls to the foreign item `panic_impl`.
 248                     // The implementation is provided by the function with the `#[panic_handler]` attribute.
 249                     "panic_impl" => {
 250                         // We don't use `check_shim` here because we are just forwarding to the lang
 251                         // item. Argument count checking will be performed when the returned `Body` is
 252                         // called.
 253                         this.check_abi_and_shim_symbol_clash(abi, Abi::Rust, link_name)?;
 254                         let panic_impl_id = tcx.lang_items().panic_impl().unwrap();
 255                         let panic_impl_instance = ty::Instance::mono(tcx, panic_impl_id);
 256                         return Ok(Some(&*this.load_mir(panic_impl_instance.def, None)?));
 257                     }
 258                     #[rustfmt::skip]
 259                     | "exit"
 260                     | "ExitProcess"
 261                     => {
 262                         let exp_abi = if link_name.as_str() == "exit" {
 263                             Abi::C { unwind: false }
 264                         } else {
 265                             Abi::System { unwind: false }
 266                         };
 267                         let &[ref code] = this.check_shim(abi, exp_abi, link_name, args)?;
 268                         // it's really u32 for ExitProcess, but we have to put it into the `Exit` variant anyway
 269                         let code = this.read_scalar(code)?.to_i32()?;
 270                         throw_machine_stop!(TerminationInfo::Exit(code.into()));
 271                     }
 272                     "abort" => {
 273                         let &[] =
 274                             this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 275                         throw_machine_stop!(TerminationInfo::Abort(
 276                             "the program aborted execution".to_owned()
 277                         ))
 278                     }
 279                     _ => {
 280                         if let Some(body) = this.lookup_exported_symbol(link_name)? {
 281                             return Ok(Some(body));
 282                         }
 283                         this.handle_unsupported(format!(
 284                             "can't call (diverging) foreign function: {}",
 285                             link_name
 286                         ))?;
 287                         return Ok(None);
 288                     }
 289                 },
 290             Some(p) => p,
 291         };
 292
 293         // Second: functions that return.
 294         match this.emulate_foreign_item_by_name(link_name, abi, args, dest, ret)? {
 295             EmulateByNameResult::NeedsJumping => {
 296                 trace!("{:?}", this.dump_place(**dest));
 297                 this.go_to_block(ret);
 298             }
 299             EmulateByNameResult::AlreadyJumped => (),
 300             EmulateByNameResult::MirBody(mir) => return Ok(Some(mir)),
 301             EmulateByNameResult::NotSupported => {
 302                 if let Some(body) = this.lookup_exported_symbol(link_name)? {
 303                     return Ok(Some(body));
 304                 }
 305
 306                 this.handle_unsupported(format!("can't call foreign function: {}", link_name))?;
 307                 return Ok(None);
 308             }
 309         }
 310
 311         Ok(None)
 312     }
 313
 314     /// Emulates calling the internal __rust_* allocator functions
 315     fn emulate_allocator(
 316         &mut self,
 317         symbol: Symbol,
 318         default: impl FnOnce(&mut MiriEvalContext<'mir, 'tcx>) -> InterpResult<'tcx>,
 319     ) -> InterpResult<'tcx, EmulateByNameResult<'mir, 'tcx>> {
 320         let this = self.eval_context_mut();
 321
 322         let allocator_kind = if let Some(allocator_kind) = this.tcx.allocator_kind(()) {
 323             allocator_kind
 324         } else {
 325             // in real code, this symbol does not exist without an allocator
 326             return Ok(EmulateByNameResult::NotSupported);
 327         };
 328
 329         match allocator_kind {
 330             AllocatorKind::Global => {
 331                 let body = this
 332                     .lookup_exported_symbol(symbol)?
 333                     .expect("symbol should be present if there is a global allocator");
 334
 335                 Ok(EmulateByNameResult::MirBody(body))
 336             }
 337             AllocatorKind::Default => {
 338                 default(this)?;
 339                 Ok(EmulateByNameResult::NeedsJumping)
 340             }
 341         }
 342     }
 343
 344     /// Emulates calling a foreign item using its name.
 345     fn emulate_foreign_item_by_name(
 346         &mut self,
 347         link_name: Symbol,
 348         abi: Abi,
 349         args: &[OpTy<'tcx, Tag>],
 350         dest: &PlaceTy<'tcx, Tag>,
 351         ret: mir::BasicBlock,
 352     ) -> InterpResult<'tcx, EmulateByNameResult<'mir, 'tcx>> {
 353         let this = self.eval_context_mut();
 354
 355         // Here we dispatch all the shims for foreign functions. If you have a platform specific
 356         // shim, add it to the corresponding submodule.
 357         match &*link_name.as_str() {
 358             // Miri-specific extern functions
 359             "miri_static_root" => {
 360                 let &[ref ptr] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 361                 let ptr = this.read_pointer(ptr)?;
 362                 let (alloc_id, offset, _) = this.memory.ptr_get_alloc(ptr)?;
 363                 if offset != Size::ZERO {
 364                     throw_unsup_format!("pointer passed to miri_static_root must point to beginning of an allocated block");
 365                 }
 366                 this.machine.static_roots.push(alloc_id);
 367             }
 368
 369             // Obtains a Miri backtrace. See the README for details.
 370             "miri_get_backtrace" => {
 371                 // `check_shim` happens inside `handle_miri_get_backtrace`.
 372                 this.handle_miri_get_backtrace(abi, link_name, args, dest)?;
 373             }
 374
 375             // Resolves a Miri backtrace frame. See the README for details.
 376             "miri_resolve_frame" => {
 377                 // `check_shim` happens inside `handle_miri_resolve_frame`.
 378                 this.handle_miri_resolve_frame(abi, link_name, args, dest)?;
 379             }
 380
 381
 382             // Standard C allocation
 383             "malloc" => {
 384                 let &[ref size] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 385                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
 386                 let res = this.malloc(size, /*zero_init:*/ false, MiriMemoryKind::C)?;
 387                 this.write_pointer(res, dest)?;
 388             }
 389             "calloc" => {
 390                 let &[ref items, ref len] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 391                 let items = this.read_scalar(items)?.to_machine_usize(this)?;
 392                 let len = this.read_scalar(len)?.to_machine_usize(this)?;
 393                 let size =
 394                     items.checked_mul(len).ok_or_else(|| err_ub_format!("overflow during calloc size computation"))?;
 395                 let res = this.malloc(size, /*zero_init:*/ true, MiriMemoryKind::C)?;
 396                 this.write_pointer(res, dest)?;
 397             }
 398             "free" => {
 399                 let &[ref ptr] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 400                 let ptr = this.read_pointer(ptr)?;
 401                 this.free(ptr, MiriMemoryKind::C)?;
 402             }
 403             "realloc" => {
 404                 let &[ref old_ptr, ref new_size] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 405                 let old_ptr = this.read_pointer(old_ptr)?;
 406                 let new_size = this.read_scalar(new_size)?.to_machine_usize(this)?;
 407                 let res = this.realloc(old_ptr, new_size, MiriMemoryKind::C)?;
 408                 this.write_pointer(res, dest)?;
 409             }
 410
 411             // Rust allocation
 412             "__rust_alloc" => {
 413                 let &[ref size, ref align] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 414                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
 415                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 416
 417                 return this.emulate_allocator(Symbol::intern("__rg_alloc"), |this| {
 418                     Self::check_alloc_request(size, align)?;
 419
 420                     let ptr = this.memory.allocate(
 421                         Size::from_bytes(size),
 422                         Align::from_bytes(align).unwrap(),
 423                         MiriMemoryKind::Rust.into(),
 424                     )?;
 425
 426                     this.write_pointer(ptr, dest)
 427                 });
 428             }
 429             "__rust_alloc_zeroed" => {
 430                 let &[ref size, ref align] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 431                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
 432                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 433
 434                 return this.emulate_allocator(Symbol::intern("__rg_alloc_zeroed"), |this| {
 435                     Self::check_alloc_request(size, align)?;
 436
 437                     let ptr = this.memory.allocate(
 438                         Size::from_bytes(size),
 439                         Align::from_bytes(align).unwrap(),
 440                         MiriMemoryKind::Rust.into(),
 441                     )?;
 442
 443                     // We just allocated this, the access is definitely in-bounds.
 444                     this.memory.write_bytes(ptr.into(), iter::repeat(0u8).take(usize::try_from(size).unwrap())).unwrap();
 445                     this.write_pointer(ptr, dest)
 446                 });
 447             }
 448             "__rust_dealloc" => {
 449                 let &[ref ptr, ref old_size, ref align] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 450                 let ptr = this.read_pointer(ptr)?;
 451                 let old_size = this.read_scalar(old_size)?.to_machine_usize(this)?;
 452                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 453
 454                 return this.emulate_allocator(Symbol::intern("__rg_dealloc"), |this| {
 455                     // No need to check old_size/align; we anyway check that they match the allocation.
 456                     this.memory.deallocate(
 457                         ptr,
 458                         Some((Size::from_bytes(old_size), Align::from_bytes(align).unwrap())),
 459                         MiriMemoryKind::Rust.into(),
 460                     )
 461                 });
 462             }
 463             "__rust_realloc" => {
 464                 let &[ref ptr, ref old_size, ref align, ref new_size] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 465                 let ptr = this.read_pointer(ptr)?;
 466                 let old_size = this.read_scalar(old_size)?.to_machine_usize(this)?;
 467                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 468                 let new_size = this.read_scalar(new_size)?.to_machine_usize(this)?;
 469                 // No need to check old_size; we anyway check that they match the allocation.
 470
 471                 return this.emulate_allocator(Symbol::intern("__rg_realloc"), |this| {
 472                     Self::check_alloc_request(new_size, align)?;
 473
 474                     let align = Align::from_bytes(align).unwrap();
 475                     let new_ptr = this.memory.reallocate(
 476                         ptr,
 477                         Some((Size::from_bytes(old_size), align)),
 478                         Size::from_bytes(new_size),
 479                         align,
 480                         MiriMemoryKind::Rust.into(),
 481                     )?;
 482                     this.write_pointer(new_ptr, dest)
 483                 });
 484             }
 485
 486             // C memory handling functions
 487             "memcmp" => {
 488                 let &[ref left, ref right, ref n] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 489                 let left = this.read_pointer(left)?;
 490                 let right = this.read_pointer(right)?;
 491                 let n = Size::from_bytes(this.read_scalar(n)?.to_machine_usize(this)?);
 492
 493                 let result = {
 494                     let left_bytes = this.memory.read_bytes(left, n)?;
 495                     let right_bytes = this.memory.read_bytes(right, n)?;
 496
 497                     use std::cmp::Ordering::*;
 498                     match left_bytes.cmp(right_bytes) {
 499                         Less => -1i32,
 500                         Equal => 0,
 501                         Greater => 1,
 502                     }
 503                 };
 504
 505                 this.write_scalar(Scalar::from_i32(result), dest)?;
 506             }
 507             "memrchr" => {
 508                 let &[ref ptr, ref val, ref num] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 509                 let ptr = this.read_pointer(ptr)?;
 510                 let val = this.read_scalar(val)?.to_i32()? as u8;
 511                 let num = this.read_scalar(num)?.to_machine_usize(this)?;
 512                 if let Some(idx) = this
 513                     .memory
 514                     .read_bytes(ptr, Size::from_bytes(num))?
 515                     .iter()
 516                     .rev()
 517                     .position(|&c| c == val)
 518                 {
 519                     let new_ptr = ptr.offset(Size::from_bytes(num - idx as u64 - 1), this)?;
 520                     this.write_pointer(new_ptr, dest)?;
 521                 } else {
 522                     this.write_null(dest)?;
 523                 }
 524             }
 525             "memchr" => {
 526                 let &[ref ptr, ref val, ref num] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 527                 let ptr = this.read_pointer(ptr)?;
 528                 let val = this.read_scalar(val)?.to_i32()? as u8;
 529                 let num = this.read_scalar(num)?.to_machine_usize(this)?;
 530                 let idx = this
 531                     .memory
 532                     .read_bytes(ptr, Size::from_bytes(num))?
 533                     .iter()
 534                     .position(|&c| c == val);
 535                 if let Some(idx) = idx {
 536                     let new_ptr = ptr.offset(Size::from_bytes(idx as u64), this)?;
 537                     this.write_pointer(new_ptr, dest)?;
 538                 } else {
 539                     this.write_null(dest)?;
 540                 }
 541             }
 542             "strlen" => {
 543                 let &[ref ptr] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 544                 let ptr = this.read_pointer(ptr)?;
 545                 let n = this.read_c_str(ptr)?.len();
 546                 this.write_scalar(Scalar::from_machine_usize(u64::try_from(n).unwrap(), this), dest)?;
 547             }
 548
 549             // math functions
 550             #[rustfmt::skip]
 551             | "cbrtf"
 552             | "coshf"
 553             | "sinhf"
 554             | "tanf"
 555             | "acosf"
 556             | "asinf"
 557             | "atanf"
 558             => {
 559                 let &[ref f] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 560                 // FIXME: Using host floats.
 561                 let f = f32::from_bits(this.read_scalar(f)?.to_u32()?);
 562                 let f = match &*link_name.as_str() {
 563                     "cbrtf" => f.cbrt(),
 564                     "coshf" => f.cosh(),
 565                     "sinhf" => f.sinh(),
 566                     "tanf" => f.tan(),
 567                     "acosf" => f.acos(),
 568                     "asinf" => f.asin(),
 569                     "atanf" => f.atan(),
 570                     _ => bug!(),
 571                 };
 572                 this.write_scalar(Scalar::from_u32(f.to_bits()), dest)?;
 573             }
 574             #[rustfmt::skip]
 575             | "_hypotf"
 576             | "hypotf"
 577             | "atan2f"
 578             => {
 579                 let &[ref f1, ref f2] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 580                 // underscore case for windows, here and below
 581                 // (see https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/floating-point-primitives?view=vs-2019)
 582                 // FIXME: Using host floats.
 583                 let f1 = f32::from_bits(this.read_scalar(f1)?.to_u32()?);
 584                 let f2 = f32::from_bits(this.read_scalar(f2)?.to_u32()?);
 585                 let n = match &*link_name.as_str() {
 586                     "_hypotf" | "hypotf" => f1.hypot(f2),
 587                     "atan2f" => f1.atan2(f2),
 588                     _ => bug!(),
 589                 };
 590                 this.write_scalar(Scalar::from_u32(n.to_bits()), dest)?;
 591             }
 592             #[rustfmt::skip]
 593             | "cbrt"
 594             | "cosh"
 595             | "sinh"
 596             | "tan"
 597             | "acos"
 598             | "asin"
 599             | "atan"
 600             => {
 601                 let &[ref f] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 602                 // FIXME: Using host floats.
 603                 let f = f64::from_bits(this.read_scalar(f)?.to_u64()?);
 604                 let f = match &*link_name.as_str() {
 605                     "cbrt" => f.cbrt(),
 606                     "cosh" => f.cosh(),
 607                     "sinh" => f.sinh(),
 608                     "tan" => f.tan(),
 609                     "acos" => f.acos(),
 610                     "asin" => f.asin(),
 611                     "atan" => f.atan(),
 612                     _ => bug!(),
 613                 };
 614                 this.write_scalar(Scalar::from_u64(f.to_bits()), dest)?;
 615             }
 616             #[rustfmt::skip]
 617             | "_hypot"
 618             | "hypot"
 619             | "atan2"
 620             => {
 621                 let &[ref f1, ref f2] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 622                 // FIXME: Using host floats.
 623                 let f1 = f64::from_bits(this.read_scalar(f1)?.to_u64()?);
 624                 let f2 = f64::from_bits(this.read_scalar(f2)?.to_u64()?);
 625                 let n = match &*link_name.as_str() {
 626                     "_hypot" | "hypot" => f1.hypot(f2),
 627                     "atan2" => f1.atan2(f2),
 628                     _ => bug!(),
 629                 };
 630                 this.write_scalar(Scalar::from_u64(n.to_bits()), dest)?;
 631             }
 632             #[rustfmt::skip]
 633             | "_ldexp"
 634             | "ldexp"
 635             | "scalbn"
 636             => {
 637                 let &[ref x, ref exp] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 638                 // For radix-2 (binary) systems, `ldexp` and `scalbn` are the same.
 639                 let x = this.read_scalar(x)?.to_f64()?;
 640                 let exp = this.read_scalar(exp)?.to_i32()?;
 641
 642                 // Saturating cast to i16. Even those are outside the valid exponent range to
 643                 // `scalbn` below will do its over/underflow handling.
 644                 let exp = if exp > i32::from(i16::MAX) {
 645                     i16::MAX
 646                 } else if exp < i32::from(i16::MIN) {
 647                     i16::MIN
 648                 } else {
 649                     exp.try_into().unwrap()
 650                 };
 651
 652                 let res = x.scalbn(exp);
 653                 this.write_scalar(Scalar::from_f64(res), dest)?;
 654             }
 655
 656             // Architecture-specific shims
 657             "llvm.x86.sse2.pause" if this.tcx.sess.target.arch == "x86" || this.tcx.sess.target.arch == "x86_64" => {
 658                 let &[] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 659                 this.yield_active_thread();
 660             }
 661             "llvm.aarch64.isb" if this.tcx.sess.target.arch == "aarch64" => {
 662                 let &[ref arg] = this.check_shim(abi, Abi::Unadjusted, link_name, args)?;
 663                 let arg = this.read_scalar(arg)?.to_i32()?;
 664                 match arg {
 665                     15 => { // SY ("full system scope")
 666                         this.yield_active_thread();
 667                     }
 668                     _ => {
 669                         throw_unsup_format!("unsupported llvm.aarch64.isb argument {}", arg);
 670                     }
 671                 }
 672             }
 673
 674             // Platform-specific shims
 675             _ => match this.tcx.sess.target.os.as_str() {
 676                 "linux" | "macos" => return shims::posix::foreign_items::EvalContextExt::emulate_foreign_item_by_name(this, link_name, abi, args, dest, ret),
 677                 "windows" => return shims::windows::foreign_items::EvalContextExt::emulate_foreign_item_by_name(this, link_name, abi, args, dest, ret),
 678                 target => throw_unsup_format!("the target `{}` is not supported", target),
 679             }
 680         };
 681
 682         // We only fall through to here if we did *not* hit the `_` arm above,
 683         // i.e., if we actually emulated the function.
 684         Ok(EmulateByNameResult::NeedsJumping)
 685     }
 686
 687     /// Check some basic requirements for this allocation request:
 688     /// non-zero size, power-of-two alignment.
 689     fn check_alloc_request(size: u64, align: u64) -> InterpResult<'tcx> {
 690         if size == 0 {
 691             throw_ub_format!("creating allocation with size 0");
 692         }
 693         if !align.is_power_of_two() {
 694             throw_ub_format!("creating allocation with non-power-of-two alignment {}", align);
 695         }
 696         Ok(())
 697     }
 698 }