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_hir::{
  10     def::DefKind,
  11     def_id::{CrateNum, DefId, LOCAL_CRATE},
  12 };
  13 use rustc_middle::middle::{
  14     codegen_fn_attrs::CodegenFnAttrFlags, dependency_format::Linkage,
  15     exported_symbols::ExportedSymbol,
  16 };
  17 use rustc_middle::mir;
  18 use rustc_middle::ty;
  19 use rustc_session::config::CrateType;
  20 use rustc_span::{symbol::sym, Symbol};
  21 use rustc_target::{
  22     abi::{Align, Size},
  23     spec::abi::Abi,
  24 };
  25
  26 use super::backtrace::EvalContextExt as _;
  27 use crate::*;
  28 use helpers::check_arg_count;
  29
  30 /// Returned by `emulate_foreign_item_by_name`.
  31 pub enum EmulateByNameResult {
  32     /// The caller is expected to jump to the return block.
  33     NeedsJumping,
  34     /// Jumping has already been taken care of.
  35     AlreadyJumped,
  36     /// The item is not supported.
  37     NotSupported,
  38 }
  39
  40 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
  41 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
  42     /// Returns the minimum alignment for the target architecture for allocations of the given size.
  43     fn min_align(&self, size: u64, kind: MiriMemoryKind) -> Align {
  44         let this = self.eval_context_ref();
  45         // List taken from `libstd/sys_common/alloc.rs`.
  46         let min_align = match this.tcx.sess.target.arch.as_str() {
  47             "x86" | "arm" | "mips" | "powerpc" | "powerpc64" | "asmjs" | "wasm32" => 8,
  48             "x86_64" | "aarch64" | "mips64" | "s390x" | "sparc64" => 16,
  49             arch => bug!("Unsupported target architecture: {}", arch),
  50         };
  51         // Windows always aligns, even small allocations.
  52         // Source: <https://support.microsoft.com/en-us/help/286470/how-to-use-pageheap-exe-in-windows-xp-windows-2000-and-windows-server>
  53         // But jemalloc does not, so for the C heap we only align if the allocation is sufficiently big.
  54         if kind == MiriMemoryKind::WinHeap || size >= min_align {
  55             return Align::from_bytes(min_align).unwrap();
  56         }
  57         // We have `size < min_align`. Round `size` *down* to the next power of two and use that.
  58         fn prev_power_of_two(x: u64) -> u64 {
  59             let next_pow2 = x.next_power_of_two();
  60             if next_pow2 == x {
  61                 // x *is* a power of two, just use that.
  62                 x
  63             } else {
  64                 // x is between two powers, so next = 2*prev.
  65                 next_pow2 / 2
  66             }
  67         }
  68         Align::from_bytes(prev_power_of_two(size)).unwrap()
  69     }
  70
  71     fn malloc(&mut self, size: u64, zero_init: bool, kind: MiriMemoryKind) -> Scalar<Tag> {
  72         let this = self.eval_context_mut();
  73         if size == 0 {
  74             Scalar::null_ptr(this)
  75         } else {
  76             let align = this.min_align(size, kind);
  77             let ptr = this.memory.allocate(Size::from_bytes(size), align, kind.into());
  78             if zero_init {
  79                 // We just allocated this, the access is definitely in-bounds.
  80                 this.memory.write_bytes(ptr.into(), iter::repeat(0u8).take(size as usize)).unwrap();
  81             }
  82             Scalar::Ptr(ptr)
  83         }
  84     }
  85
  86     fn free(&mut self, ptr: Scalar<Tag>, kind: MiriMemoryKind) -> InterpResult<'tcx> {
  87         let this = self.eval_context_mut();
  88         if !this.is_null(ptr)? {
  89             let ptr = this.force_ptr(ptr)?;
  90             this.memory.deallocate(ptr, None, kind.into())?;
  91         }
  92         Ok(())
  93     }
  94
  95     fn realloc(
  96         &mut self,
  97         old_ptr: Scalar<Tag>,
  98         new_size: u64,
  99         kind: MiriMemoryKind,
 100     ) -> InterpResult<'tcx, Scalar<Tag>> {
 101         let this = self.eval_context_mut();
 102         let new_align = this.min_align(new_size, kind);
 103         if this.is_null(old_ptr)? {
 104             if new_size == 0 {
 105                 Ok(Scalar::null_ptr(this))
 106             } else {
 107                 let new_ptr =
 108                     this.memory.allocate(Size::from_bytes(new_size), new_align, kind.into());
 109                 Ok(Scalar::Ptr(new_ptr))
 110             }
 111         } else {
 112             let old_ptr = this.force_ptr(old_ptr)?;
 113             if new_size == 0 {
 114                 this.memory.deallocate(old_ptr, None, kind.into())?;
 115                 Ok(Scalar::null_ptr(this))
 116             } else {
 117                 let new_ptr = this.memory.reallocate(
 118                     old_ptr,
 119                     None,
 120                     Size::from_bytes(new_size),
 121                     new_align,
 122                     kind.into(),
 123                 )?;
 124                 Ok(Scalar::Ptr(new_ptr))
 125             }
 126         }
 127     }
 128
 129     /// Lookup the body of a function that has `link_name` as the symbol name.
 130     fn lookup_exported_symbol(
 131         &mut self,
 132         link_name: Symbol,
 133     ) -> InterpResult<'tcx, Option<&'mir mir::Body<'tcx>>> {
 134         let this = self.eval_context_mut();
 135         let tcx = this.tcx.tcx;
 136
 137         // If the result was cached, just return it.
 138         if let Some(instance) = this.machine.exported_symbols_cache.get(&link_name) {
 139             return Ok(Some(this.load_mir(instance.def, None)?));
 140         }
 141
 142         // Find it if it was not cached.
 143         let mut instance_and_crate: Option<(ty::Instance<'_>, CrateNum)> = None;
 144         // `dependency_formats` includes all the transitive informations needed to link a crate,
 145         // which is what we need here since we need to dig out `exported_symbols` from all transitive
 146         // dependencies.
 147         let dependency_formats = tcx.dependency_formats(());
 148         let dependency_format = dependency_formats
 149             .iter()
 150             .find(|(crate_type, _)| *crate_type == CrateType::Executable)
 151             .expect("interpreting a non-executable crate");
 152         for cnum in
 153             iter::once(LOCAL_CRATE).chain(dependency_format.1.iter().enumerate().filter_map(
 154                 |(num, &linkage)| (linkage != Linkage::NotLinked).then_some(CrateNum::new(num + 1)),
 155             ))
 156         {
 157             // We can ignore `_export_level` here: we are a Rust crate, and everything is exported
 158             // from a Rust crate.
 159             for &(symbol, _export_level) in tcx.exported_symbols(cnum) {
 160                 if let ExportedSymbol::NonGeneric(def_id) = symbol {
 161                     let attrs = tcx.codegen_fn_attrs(def_id);
 162                     let symbol_name = if let Some(export_name) = attrs.export_name {
 163                         export_name
 164                     } else if attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE) {
 165                         tcx.item_name(def_id)
 166                     } else {
 167                         // Skip over items without an explicitly defined symbol name.
 168                         continue;
 169                     };
 170                     if symbol_name == link_name {
 171                         if let Some((instance, original_cnum)) = instance_and_crate {
 172                             throw_machine_stop!(TerminationInfo::MultipleSymbolDefinitions {
 173                                 link_name,
 174                                 first: tcx.def_span(instance.def_id()).data(),
 175                                 first_crate: tcx.crate_name(original_cnum),
 176                                 second: tcx.def_span(def_id).data(),
 177                                 second_crate: tcx.crate_name(cnum),
 178                             });
 179                         }
 180                         if !matches!(tcx.def_kind(def_id), DefKind::Fn | DefKind::AssocFn) {
 181                             throw_ub_format!(
 182                                 "attempt to call an exported symbol that is not defined as a function"
 183                             );
 184                         }
 185                         instance_and_crate = Some((ty::Instance::mono(tcx, def_id), cnum));
 186                     }
 187                 }
 188             }
 189         }
 190
 191         // Cache it and load its MIR, if found.
 192         instance_and_crate
 193             .map(|(instance, _)| {
 194                 this.machine.exported_symbols_cache.insert(link_name, instance);
 195                 this.load_mir(instance.def, None)
 196             })
 197             .transpose()
 198     }
 199
 200     /// Emulates calling a foreign item, failing if the item is not supported.
 201     /// This function will handle `goto_block` if needed.
 202     /// Returns Ok(None) if the foreign item was completely handled
 203     /// by this function.
 204     /// Returns Ok(Some(body)) if processing the foreign item
 205     /// is delegated to another function.
 206     fn emulate_foreign_item(
 207         &mut self,
 208         def_id: DefId,
 209         abi: Abi,
 210         args: &[OpTy<'tcx, Tag>],
 211         ret: Option<(&PlaceTy<'tcx, Tag>, mir::BasicBlock)>,
 212         unwind: StackPopUnwind,
 213     ) -> InterpResult<'tcx, Option<&'mir mir::Body<'tcx>>> {
 214         let this = self.eval_context_mut();
 215         let attrs = this.tcx.get_attrs(def_id);
 216         let link_name_sym = this
 217             .tcx
 218             .sess
 219             .first_attr_value_str_by_name(&attrs, sym::link_name)
 220             .unwrap_or_else(|| this.tcx.item_name(def_id));
 221         let link_name = link_name_sym.as_str();
 222         // Strip linker suffixes (seen on 32-bit macOS).
 223         let link_name = link_name.trim_end_matches("$UNIX2003");
 224         let tcx = this.tcx.tcx;
 225
 226         // First: functions that diverge.
 227         let (dest, ret) = match ret {
 228             None => match link_name {
 229                 "miri_start_panic" => {
 230                     this.check_abi(abi, Abi::Rust)?;
 231                     this.handle_miri_start_panic(args, unwind)?;
 232                     return Ok(None);
 233                 }
 234                 // This matches calls to the foreign item `panic_impl`.
 235                 // The implementation is provided by the function with the `#[panic_handler]` attribute.
 236                 "panic_impl" => {
 237                     this.check_abi(abi, Abi::Rust)?;
 238                     let panic_impl_id = tcx.lang_items().panic_impl().unwrap();
 239                     let panic_impl_instance = ty::Instance::mono(tcx, panic_impl_id);
 240                     return Ok(Some(&*this.load_mir(panic_impl_instance.def, None)?));
 241                 }
 242                 #[rustfmt::skip]
 243                 | "exit"
 244                 | "ExitProcess"
 245                 => {
 246                     this.check_abi(abi, if link_name == "exit" { Abi::C { unwind: false } } else { Abi::System { unwind: false } })?;
 247                     let &[ref code] = check_arg_count(args)?;
 248                     // it's really u32 for ExitProcess, but we have to put it into the `Exit` variant anyway
 249                     let code = this.read_scalar(code)?.to_i32()?;
 250                     throw_machine_stop!(TerminationInfo::Exit(code.into()));
 251                 }
 252                 "abort" => {
 253                     this.check_abi(abi, Abi::C { unwind: false })?;
 254                     throw_machine_stop!(TerminationInfo::Abort(
 255                         "the program aborted execution".to_owned()
 256                     ))
 257                 }
 258                 _ => {
 259                     if let Some(body) = this.lookup_exported_symbol(link_name_sym)? {
 260                         return Ok(Some(body));
 261                     }
 262                     this.handle_unsupported(format!(
 263                         "can't call (diverging) foreign function: {}",
 264                         link_name
 265                     ))?;
 266                     return Ok(None);
 267                 }
 268             },
 269             Some(p) => p,
 270         };
 271
 272         // Second: functions that return.
 273         match this.emulate_foreign_item_by_name(link_name, abi, args, dest, ret)? {
 274             EmulateByNameResult::NeedsJumping => {
 275                 trace!("{:?}", this.dump_place(**dest));
 276                 this.go_to_block(ret);
 277             }
 278             EmulateByNameResult::AlreadyJumped => (),
 279             EmulateByNameResult::NotSupported => {
 280                 if let Some(body) = this.lookup_exported_symbol(link_name_sym)? {
 281                     return Ok(Some(body));
 282                 }
 283
 284                 this.handle_unsupported(format!("can't call foreign function: {}", link_name))?;
 285                 return Ok(None);
 286             }
 287         }
 288
 289         Ok(None)
 290     }
 291
 292     /// Emulates calling a foreign item using its name.
 293     fn emulate_foreign_item_by_name(
 294         &mut self,
 295         link_name: &str,
 296         abi: Abi,
 297         args: &[OpTy<'tcx, Tag>],
 298         dest: &PlaceTy<'tcx, Tag>,
 299         ret: mir::BasicBlock,
 300     ) -> InterpResult<'tcx, EmulateByNameResult> {
 301         let this = self.eval_context_mut();
 302
 303         // Here we dispatch all the shims for foreign functions. If you have a platform specific
 304         // shim, add it to the corresponding submodule.
 305         match link_name {
 306             // Miri-specific extern functions
 307             "miri_static_root" => {
 308                 this.check_abi(abi, Abi::Rust)?;
 309                 let &[ref ptr] = check_arg_count(args)?;
 310                 let ptr = this.read_scalar(ptr)?.check_init()?;
 311                 let ptr = this.force_ptr(ptr)?;
 312                 if ptr.offset != Size::ZERO {
 313                     throw_unsup_format!("pointer passed to miri_static_root must point to beginning of an allocated block");
 314                 }
 315                 this.machine.static_roots.push(ptr.alloc_id);
 316             }
 317
 318             // Obtains a Miri backtrace. See the README for details.
 319             "miri_get_backtrace" => {
 320                 this.check_abi(abi, Abi::Rust)?;
 321                 this.handle_miri_get_backtrace(args, dest)?;
 322             }
 323
 324             // Resolves a Miri backtrace frame. See the README for details.
 325             "miri_resolve_frame" => {
 326                 this.check_abi(abi, Abi::Rust)?;
 327                 this.handle_miri_resolve_frame(args, dest)?;
 328             }
 329
 330
 331             // Standard C allocation
 332             "malloc" => {
 333                 this.check_abi(abi, Abi::C { unwind: false })?;
 334                 let &[ref size] = check_arg_count(args)?;
 335                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
 336                 let res = this.malloc(size, /*zero_init:*/ false, MiriMemoryKind::C);
 337                 this.write_scalar(res, dest)?;
 338             }
 339             "calloc" => {
 340                 this.check_abi(abi, Abi::C { unwind: false })?;
 341                 let &[ref items, ref len] = check_arg_count(args)?;
 342                 let items = this.read_scalar(items)?.to_machine_usize(this)?;
 343                 let len = this.read_scalar(len)?.to_machine_usize(this)?;
 344                 let size =
 345                     items.checked_mul(len).ok_or_else(|| err_ub_format!("overflow during calloc size computation"))?;
 346                 let res = this.malloc(size, /*zero_init:*/ true, MiriMemoryKind::C);
 347                 this.write_scalar(res, dest)?;
 348             }
 349             "free" => {
 350                 this.check_abi(abi, Abi::C { unwind: false })?;
 351                 let &[ref ptr] = check_arg_count(args)?;
 352                 let ptr = this.read_scalar(ptr)?.check_init()?;
 353                 this.free(ptr, MiriMemoryKind::C)?;
 354             }
 355             "realloc" => {
 356                 this.check_abi(abi, Abi::C { unwind: false })?;
 357                 let &[ref old_ptr, ref new_size] = check_arg_count(args)?;
 358                 let old_ptr = this.read_scalar(old_ptr)?.check_init()?;
 359                 let new_size = this.read_scalar(new_size)?.to_machine_usize(this)?;
 360                 let res = this.realloc(old_ptr, new_size, MiriMemoryKind::C)?;
 361                 this.write_scalar(res, dest)?;
 362             }
 363
 364             // Rust allocation
 365             // (Usually these would be forwarded to to `#[global_allocator]`; we instead implement a generic
 366             // allocation that also checks that all conditions are met, such as not permitting zero-sized allocations.)
 367             "__rust_alloc" => {
 368                 this.check_abi(abi, Abi::Rust)?;
 369                 let &[ref size, ref align] = check_arg_count(args)?;
 370                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
 371                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 372                 Self::check_alloc_request(size, align)?;
 373                 let ptr = this.memory.allocate(
 374                     Size::from_bytes(size),
 375                     Align::from_bytes(align).unwrap(),
 376                     MiriMemoryKind::Rust.into(),
 377                 );
 378                 this.write_scalar(ptr, dest)?;
 379             }
 380             "__rust_alloc_zeroed" => {
 381                 this.check_abi(abi, Abi::Rust)?;
 382                 let &[ref size, ref align] = check_arg_count(args)?;
 383                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
 384                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 385                 Self::check_alloc_request(size, align)?;
 386                 let ptr = this.memory.allocate(
 387                     Size::from_bytes(size),
 388                     Align::from_bytes(align).unwrap(),
 389                     MiriMemoryKind::Rust.into(),
 390                 );
 391                 // We just allocated this, the access is definitely in-bounds.
 392                 this.memory.write_bytes(ptr.into(), iter::repeat(0u8).take(usize::try_from(size).unwrap())).unwrap();
 393                 this.write_scalar(ptr, dest)?;
 394             }
 395             "__rust_dealloc" => {
 396                 this.check_abi(abi, Abi::Rust)?;
 397                 let &[ref ptr, ref old_size, ref align] = check_arg_count(args)?;
 398                 let ptr = this.read_scalar(ptr)?.check_init()?;
 399                 let old_size = this.read_scalar(old_size)?.to_machine_usize(this)?;
 400                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 401                 // No need to check old_size/align; we anyway check that they match the allocation.
 402                 let ptr = this.force_ptr(ptr)?;
 403                 this.memory.deallocate(
 404                     ptr,
 405                     Some((Size::from_bytes(old_size), Align::from_bytes(align).unwrap())),
 406                     MiriMemoryKind::Rust.into(),
 407                 )?;
 408             }
 409             "__rust_realloc" => {
 410                 this.check_abi(abi, Abi::Rust)?;
 411                 let &[ref ptr, ref old_size, ref align, ref new_size] = check_arg_count(args)?;
 412                 let ptr = this.force_ptr(this.read_scalar(ptr)?.check_init()?)?;
 413                 let old_size = this.read_scalar(old_size)?.to_machine_usize(this)?;
 414                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 415                 let new_size = this.read_scalar(new_size)?.to_machine_usize(this)?;
 416                 Self::check_alloc_request(new_size, align)?;
 417                 // No need to check old_size; we anyway check that they match the allocation.
 418                 let align = Align::from_bytes(align).unwrap();
 419                 let new_ptr = this.memory.reallocate(
 420                     ptr,
 421                     Some((Size::from_bytes(old_size), align)),
 422                     Size::from_bytes(new_size),
 423                     align,
 424                     MiriMemoryKind::Rust.into(),
 425                 )?;
 426                 this.write_scalar(new_ptr, dest)?;
 427             }
 428
 429             // C memory handling functions
 430             "memcmp" => {
 431                 this.check_abi(abi, Abi::C { unwind: false })?;
 432                 let &[ref left, ref right, ref n] = check_arg_count(args)?;
 433                 let left = this.read_scalar(left)?.check_init()?;
 434                 let right = this.read_scalar(right)?.check_init()?;
 435                 let n = Size::from_bytes(this.read_scalar(n)?.to_machine_usize(this)?);
 436
 437                 let result = {
 438                     let left_bytes = this.memory.read_bytes(left, n)?;
 439                     let right_bytes = this.memory.read_bytes(right, n)?;
 440
 441                     use std::cmp::Ordering::*;
 442                     match left_bytes.cmp(right_bytes) {
 443                         Less => -1i32,
 444                         Equal => 0,
 445                         Greater => 1,
 446                     }
 447                 };
 448
 449                 this.write_scalar(Scalar::from_i32(result), dest)?;
 450             }
 451             "memrchr" => {
 452                 this.check_abi(abi, Abi::C { unwind: false })?;
 453                 let &[ref ptr, ref val, ref num] = check_arg_count(args)?;
 454                 let ptr = this.read_scalar(ptr)?.check_init()?;
 455                 let val = this.read_scalar(val)?.to_i32()? as u8;
 456                 let num = this.read_scalar(num)?.to_machine_usize(this)?;
 457                 if let Some(idx) = this
 458                     .memory
 459                     .read_bytes(ptr, Size::from_bytes(num))?
 460                     .iter()
 461                     .rev()
 462                     .position(|&c| c == val)
 463                 {
 464                     let new_ptr = ptr.ptr_offset(Size::from_bytes(num - idx as u64 - 1), this)?;
 465                     this.write_scalar(new_ptr, dest)?;
 466                 } else {
 467                     this.write_null(dest)?;
 468                 }
 469             }
 470             "memchr" => {
 471                 this.check_abi(abi, Abi::C { unwind: false })?;
 472                 let &[ref ptr, ref val, ref num] = check_arg_count(args)?;
 473                 let ptr = this.read_scalar(ptr)?.check_init()?;
 474                 let val = this.read_scalar(val)?.to_i32()? as u8;
 475                 let num = this.read_scalar(num)?.to_machine_usize(this)?;
 476                 let idx = this
 477                     .memory
 478                     .read_bytes(ptr, Size::from_bytes(num))?
 479                     .iter()
 480                     .position(|&c| c == val);
 481                 if let Some(idx) = idx {
 482                     let new_ptr = ptr.ptr_offset(Size::from_bytes(idx as u64), this)?;
 483                     this.write_scalar(new_ptr, dest)?;
 484                 } else {
 485                     this.write_null(dest)?;
 486                 }
 487             }
 488             "strlen" => {
 489                 this.check_abi(abi, Abi::C { unwind: false })?;
 490                 let &[ref ptr] = check_arg_count(args)?;
 491                 let ptr = this.read_scalar(ptr)?.check_init()?;
 492                 let n = this.read_c_str(ptr)?.len();
 493                 this.write_scalar(Scalar::from_machine_usize(u64::try_from(n).unwrap(), this), dest)?;
 494             }
 495
 496             // math functions
 497             #[rustfmt::skip]
 498             | "cbrtf"
 499             | "coshf"
 500             | "sinhf"
 501             | "tanf"
 502             | "acosf"
 503             | "asinf"
 504             | "atanf"
 505             => {
 506                 this.check_abi(abi, Abi::C { unwind: false })?;
 507                 let &[ref f] = check_arg_count(args)?;
 508                 // FIXME: Using host floats.
 509                 let f = f32::from_bits(this.read_scalar(f)?.to_u32()?);
 510                 let f = match link_name {
 511                     "cbrtf" => f.cbrt(),
 512                     "coshf" => f.cosh(),
 513                     "sinhf" => f.sinh(),
 514                     "tanf" => f.tan(),
 515                     "acosf" => f.acos(),
 516                     "asinf" => f.asin(),
 517                     "atanf" => f.atan(),
 518                     _ => bug!(),
 519                 };
 520                 this.write_scalar(Scalar::from_u32(f.to_bits()), dest)?;
 521             }
 522             #[rustfmt::skip]
 523             | "_hypotf"
 524             | "hypotf"
 525             | "atan2f"
 526             => {
 527                 this.check_abi(abi, Abi::C { unwind: false })?;
 528                 let &[ref f1, ref f2] = check_arg_count(args)?;
 529                 // underscore case for windows, here and below
 530                 // (see https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/floating-point-primitives?view=vs-2019)
 531                 // FIXME: Using host floats.
 532                 let f1 = f32::from_bits(this.read_scalar(f1)?.to_u32()?);
 533                 let f2 = f32::from_bits(this.read_scalar(f2)?.to_u32()?);
 534                 let n = match link_name {
 535                     "_hypotf" | "hypotf" => f1.hypot(f2),
 536                     "atan2f" => f1.atan2(f2),
 537                     _ => bug!(),
 538                 };
 539                 this.write_scalar(Scalar::from_u32(n.to_bits()), dest)?;
 540             }
 541             #[rustfmt::skip]
 542             | "cbrt"
 543             | "cosh"
 544             | "sinh"
 545             | "tan"
 546             | "acos"
 547             | "asin"
 548             | "atan"
 549             => {
 550                 this.check_abi(abi, Abi::C { unwind: false })?;
 551                 let &[ref f] = check_arg_count(args)?;
 552                 // FIXME: Using host floats.
 553                 let f = f64::from_bits(this.read_scalar(f)?.to_u64()?);
 554                 let f = match link_name {
 555                     "cbrt" => f.cbrt(),
 556                     "cosh" => f.cosh(),
 557                     "sinh" => f.sinh(),
 558                     "tan" => f.tan(),
 559                     "acos" => f.acos(),
 560                     "asin" => f.asin(),
 561                     "atan" => f.atan(),
 562                     _ => bug!(),
 563                 };
 564                 this.write_scalar(Scalar::from_u64(f.to_bits()), dest)?;
 565             }
 566             #[rustfmt::skip]
 567             | "_hypot"
 568             | "hypot"
 569             | "atan2"
 570             => {
 571                 this.check_abi(abi, Abi::C { unwind: false })?;
 572                 let &[ref f1, ref f2] = check_arg_count(args)?;
 573                 // FIXME: Using host floats.
 574                 let f1 = f64::from_bits(this.read_scalar(f1)?.to_u64()?);
 575                 let f2 = f64::from_bits(this.read_scalar(f2)?.to_u64()?);
 576                 let n = match link_name {
 577                     "_hypot" | "hypot" => f1.hypot(f2),
 578                     "atan2" => f1.atan2(f2),
 579                     _ => bug!(),
 580                 };
 581                 this.write_scalar(Scalar::from_u64(n.to_bits()), dest)?;
 582             }
 583             #[rustfmt::skip]
 584             | "_ldexp"
 585             | "ldexp"
 586             | "scalbn"
 587             => {
 588                 this.check_abi(abi, Abi::C { unwind: false })?;
 589                 let &[ref x, ref exp] = check_arg_count(args)?;
 590                 // For radix-2 (binary) systems, `ldexp` and `scalbn` are the same.
 591                 let x = this.read_scalar(x)?.to_f64()?;
 592                 let exp = this.read_scalar(exp)?.to_i32()?;
 593
 594                 // Saturating cast to i16. Even those are outside the valid exponent range to
 595                 // `scalbn` below will do its over/underflow handling.
 596                 let exp = if exp > i32::from(i16::MAX) {
 597                     i16::MAX
 598                 } else if exp < i32::from(i16::MIN) {
 599                     i16::MIN
 600                 } else {
 601                     exp.try_into().unwrap()
 602                 };
 603
 604                 let res = x.scalbn(exp);
 605                 this.write_scalar(Scalar::from_f64(res), dest)?;
 606             }
 607
 608             // Architecture-specific shims
 609             "llvm.x86.sse2.pause" if this.tcx.sess.target.arch == "x86" || this.tcx.sess.target.arch == "x86_64" => {
 610                 this.check_abi(abi, Abi::C { unwind: false })?;
 611                 let &[] = check_arg_count(args)?;
 612                 this.yield_active_thread();
 613             }
 614             "llvm.aarch64.isb" if this.tcx.sess.target.arch == "aarch64" => {
 615                 this.check_abi(abi, Abi::C { unwind: false })?;
 616                 let &[ref arg] = check_arg_count(args)?;
 617                 let arg = this.read_scalar(arg)?.to_i32()?;
 618                 match arg {
 619                     15 => { // SY ("full system scope")
 620                         this.yield_active_thread();
 621                     }
 622                     _ => {
 623                         throw_unsup_format!("unsupported llvm.aarch64.isb argument {}", arg);
 624                     }
 625                 }
 626             }
 627
 628             // Platform-specific shims
 629             _ => match this.tcx.sess.target.os.as_str() {
 630                 "linux" | "macos" => return shims::posix::foreign_items::EvalContextExt::emulate_foreign_item_by_name(this, link_name, abi, args, dest, ret),
 631                 "windows" => return shims::windows::foreign_items::EvalContextExt::emulate_foreign_item_by_name(this, link_name, abi, args, dest, ret),
 632                 target => throw_unsup_format!("the target `{}` is not supported", target),
 633             }
 634         };
 635
 636         // We only fall through to here if we did *not* hit the `_` arm above,
 637         // i.e., if we actually emulated the function.
 638         Ok(EmulateByNameResult::NeedsJumping)
 639     }
 640
 641     /// Check some basic requirements for this allocation request:
 642     /// non-zero size, power-of-two alignment.
 643     fn check_alloc_request(size: u64, align: u64) -> InterpResult<'tcx> {
 644         if size == 0 {
 645             throw_ub_format!("creating allocation with size 0");
 646         }
 647         if !align.is_power_of_two() {
 648             throw_ub_format!("creating allocation with non-power-of-two alignment {}", align);
 649         }
 650         Ok(())
 651     }
 652 }