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_abi, 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             // FIXME: Do we need to check `SymbolExportLevel` (the `_` below)?
 158             for &(symbol, _) in tcx.exported_symbols(cnum) {
 159                 if let ExportedSymbol::NonGeneric(def_id) = symbol {
 160                     let attrs = tcx.codegen_fn_attrs(def_id);
 161                     let symbol_name = if let Some(export_name) = attrs.export_name {
 162                         export_name
 163                     } else if attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE) {
 164                         tcx.item_name(def_id)
 165                     } else {
 166                         // Skip over items without an explicitly defined symbol name.
 167                         continue;
 168                     };
 169                     if symbol_name == link_name {
 170                         if let Some((instance, original_cnum)) = instance_and_crate {
 171                             throw_machine_stop!(TerminationInfo::MultipleSymbolDefinitions {
 172                                 link_name,
 173                                 first: tcx.def_span(instance.def_id()).data(),
 174                                 first_crate: tcx.crate_name(original_cnum),
 175                                 second: tcx.def_span(def_id).data(),
 176                                 second_crate: tcx.crate_name(cnum),
 177                             });
 178                         }
 179                         if tcx.def_kind(def_id) != DefKind::Fn {
 180                             throw_ub_format!(
 181                                 "attempt to call an exported symbol that is not defined as a function"
 182                             );
 183                         }
 184                         instance_and_crate = Some((ty::Instance::mono(tcx, def_id), cnum));
 185                     }
 186                 }
 187             }
 188         }
 189
 190         // Cache it and load its MIR, if found.
 191         instance_and_crate
 192             .map(|(instance, _)| {
 193                 this.machine.exported_symbols_cache.insert(link_name, instance);
 194                 this.load_mir(instance.def, None)
 195             })
 196             .transpose()
 197     }
 198
 199     /// Emulates calling a foreign item, failing if the item is not supported.
 200     /// This function will handle `goto_block` if needed.
 201     /// Returns Ok(None) if the foreign item was completely handled
 202     /// by this function.
 203     /// Returns Ok(Some(body)) if processing the foreign item
 204     /// is delegated to another function.
 205     fn emulate_foreign_item(
 206         &mut self,
 207         def_id: DefId,
 208         abi: Abi,
 209         args: &[OpTy<'tcx, Tag>],
 210         ret: Option<(&PlaceTy<'tcx, Tag>, mir::BasicBlock)>,
 211         unwind: StackPopUnwind,
 212     ) -> InterpResult<'tcx, Option<&'mir mir::Body<'tcx>>> {
 213         let this = self.eval_context_mut();
 214         let attrs = this.tcx.get_attrs(def_id);
 215         let link_name_sym = match this.tcx.sess.first_attr_value_str_by_name(&attrs, sym::link_name)
 216         {
 217             Some(name) => name,
 218             None => this.tcx.item_name(def_id),
 219         };
 220         let link_name = link_name_sym.as_str();
 221         // Strip linker suffixes (seen on 32-bit macOS).
 222         let link_name = link_name.trim_end_matches("$UNIX2003");
 223         let tcx = this.tcx.tcx;
 224
 225         // First: functions that diverge.
 226         let (dest, ret) = match ret {
 227             None => match link_name {
 228                 "miri_start_panic" => {
 229                     check_abi(this, abi, Abi::Rust)?;
 230                     this.handle_miri_start_panic(args, unwind)?;
 231                     return Ok(None);
 232                 }
 233                 // This matches calls to the foreign item `panic_impl`.
 234                 // The implementation is provided by the function with the `#[panic_handler]` attribute.
 235                 "panic_impl" => {
 236                     check_abi(this, abi, Abi::Rust)?;
 237                     let panic_impl_id = tcx.lang_items().panic_impl().unwrap();
 238                     let panic_impl_instance = ty::Instance::mono(tcx, panic_impl_id);
 239                     return Ok(Some(&*this.load_mir(panic_impl_instance.def, None)?));
 240                 }
 241                 #[rustfmt::skip]
 242                 | "exit"
 243                 | "ExitProcess"
 244                 => {
 245                     check_abi(this, abi, if link_name == "exit" { Abi::C { unwind: false } } else { Abi::System { unwind: false } })?;
 246                     let &[ref code] = check_arg_count(args)?;
 247                     // it's really u32 for ExitProcess, but we have to put it into the `Exit` variant anyway
 248                     let code = this.read_scalar(code)?.to_i32()?;
 249                     throw_machine_stop!(TerminationInfo::Exit(code.into()));
 250                 }
 251                 "abort" => {
 252                     check_abi(this, abi, Abi::C { unwind: false })?;
 253                     throw_machine_stop!(TerminationInfo::Abort(
 254                         "the program aborted execution".to_owned()
 255                     ))
 256                 }
 257                 _ => {
 258                     if let Some(body) = this.lookup_exported_symbol(link_name_sym)? {
 259                         return Ok(Some(body));
 260                     }
 261                     throw_unsup_format!("can't call (diverging) foreign function: {}", link_name);
 262                 }
 263             },
 264             Some(p) => p,
 265         };
 266
 267         // Second: functions that return.
 268         match this.emulate_foreign_item_by_name(link_name, abi, args, dest, ret)? {
 269             EmulateByNameResult::NeedsJumping => {
 270                 trace!("{:?}", this.dump_place(**dest));
 271                 this.go_to_block(ret);
 272             }
 273             EmulateByNameResult::AlreadyJumped => (),
 274             EmulateByNameResult::NotSupported => {
 275                 if let Some(body) = this.lookup_exported_symbol(link_name_sym)? {
 276                     return Ok(Some(body));
 277                 }
 278                 throw_unsup_format!("can't call foreign function: {}", link_name);
 279             }
 280         }
 281
 282         Ok(None)
 283     }
 284
 285     /// Emulates calling a foreign item using its name.
 286     fn emulate_foreign_item_by_name(
 287         &mut self,
 288         link_name: &str,
 289         abi: Abi,
 290         args: &[OpTy<'tcx, Tag>],
 291         dest: &PlaceTy<'tcx, Tag>,
 292         ret: mir::BasicBlock,
 293     ) -> InterpResult<'tcx, EmulateByNameResult> {
 294         let this = self.eval_context_mut();
 295
 296         // Here we dispatch all the shims for foreign functions. If you have a platform specific
 297         // shim, add it to the corresponding submodule.
 298         match link_name {
 299             // Miri-specific extern functions
 300             "miri_static_root" => {
 301                 check_abi(this, abi, Abi::Rust)?;
 302                 let &[ref ptr] = check_arg_count(args)?;
 303                 let ptr = this.read_scalar(ptr)?.check_init()?;
 304                 let ptr = this.force_ptr(ptr)?;
 305                 if ptr.offset != Size::ZERO {
 306                     throw_unsup_format!("pointer passed to miri_static_root must point to beginning of an allocated block");
 307                 }
 308                 this.machine.static_roots.push(ptr.alloc_id);
 309             }
 310
 311             // Obtains a Miri backtrace. See the README for details.
 312             "miri_get_backtrace" => {
 313                 check_abi(this, abi, Abi::Rust)?;
 314                 this.handle_miri_get_backtrace(args, dest)?;
 315             }
 316
 317             // Resolves a Miri backtrace frame. See the README for details.
 318             "miri_resolve_frame" => {
 319                 check_abi(this, abi, Abi::Rust)?;
 320                 this.handle_miri_resolve_frame(args, dest)?;
 321             }
 322
 323
 324             // Standard C allocation
 325             "malloc" => {
 326                 check_abi(this, abi, Abi::C { unwind: false })?;
 327                 let &[ref size] = check_arg_count(args)?;
 328                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
 329                 let res = this.malloc(size, /*zero_init:*/ false, MiriMemoryKind::C);
 330                 this.write_scalar(res, dest)?;
 331             }
 332             "calloc" => {
 333                 check_abi(this, abi, Abi::C { unwind: false })?;
 334                 let &[ref items, ref len] = check_arg_count(args)?;
 335                 let items = this.read_scalar(items)?.to_machine_usize(this)?;
 336                 let len = this.read_scalar(len)?.to_machine_usize(this)?;
 337                 let size =
 338                     items.checked_mul(len).ok_or_else(|| err_ub_format!("overflow during calloc size computation"))?;
 339                 let res = this.malloc(size, /*zero_init:*/ true, MiriMemoryKind::C);
 340                 this.write_scalar(res, dest)?;
 341             }
 342             "free" => {
 343                 check_abi(this, abi, Abi::C { unwind: false })?;
 344                 let &[ref ptr] = check_arg_count(args)?;
 345                 let ptr = this.read_scalar(ptr)?.check_init()?;
 346                 this.free(ptr, MiriMemoryKind::C)?;
 347             }
 348             "realloc" => {
 349                 check_abi(this, abi, Abi::C { unwind: false })?;
 350                 let &[ref old_ptr, ref new_size] = check_arg_count(args)?;
 351                 let old_ptr = this.read_scalar(old_ptr)?.check_init()?;
 352                 let new_size = this.read_scalar(new_size)?.to_machine_usize(this)?;
 353                 let res = this.realloc(old_ptr, new_size, MiriMemoryKind::C)?;
 354                 this.write_scalar(res, dest)?;
 355             }
 356
 357             // Rust allocation
 358             // (Usually these would be forwarded to to `#[global_allocator]`; we instead implement a generic
 359             // allocation that also checks that all conditions are met, such as not permitting zero-sized allocations.)
 360             "__rust_alloc" => {
 361                 check_abi(this, abi, Abi::Rust)?;
 362                 let &[ref size, ref align] = check_arg_count(args)?;
 363                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
 364                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 365                 Self::check_alloc_request(size, align)?;
 366                 let ptr = this.memory.allocate(
 367                     Size::from_bytes(size),
 368                     Align::from_bytes(align).unwrap(),
 369                     MiriMemoryKind::Rust.into(),
 370                 );
 371                 this.write_scalar(ptr, dest)?;
 372             }
 373             "__rust_alloc_zeroed" => {
 374                 check_abi(this, abi, Abi::Rust)?;
 375                 let &[ref size, ref align] = check_arg_count(args)?;
 376                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
 377                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 378                 Self::check_alloc_request(size, align)?;
 379                 let ptr = this.memory.allocate(
 380                     Size::from_bytes(size),
 381                     Align::from_bytes(align).unwrap(),
 382                     MiriMemoryKind::Rust.into(),
 383                 );
 384                 // We just allocated this, the access is definitely in-bounds.
 385                 this.memory.write_bytes(ptr.into(), iter::repeat(0u8).take(usize::try_from(size).unwrap())).unwrap();
 386                 this.write_scalar(ptr, dest)?;
 387             }
 388             "__rust_dealloc" => {
 389                 check_abi(this, abi, Abi::Rust)?;
 390                 let &[ref ptr, ref old_size, ref align] = check_arg_count(args)?;
 391                 let ptr = this.read_scalar(ptr)?.check_init()?;
 392                 let old_size = this.read_scalar(old_size)?.to_machine_usize(this)?;
 393                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 394                 // No need to check old_size/align; we anyway check that they match the allocation.
 395                 let ptr = this.force_ptr(ptr)?;
 396                 this.memory.deallocate(
 397                     ptr,
 398                     Some((Size::from_bytes(old_size), Align::from_bytes(align).unwrap())),
 399                     MiriMemoryKind::Rust.into(),
 400                 )?;
 401             }
 402             "__rust_realloc" => {
 403                 check_abi(this, abi, Abi::Rust)?;
 404                 let &[ref ptr, ref old_size, ref align, ref new_size] = check_arg_count(args)?;
 405                 let ptr = this.force_ptr(this.read_scalar(ptr)?.check_init()?)?;
 406                 let old_size = this.read_scalar(old_size)?.to_machine_usize(this)?;
 407                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 408                 let new_size = this.read_scalar(new_size)?.to_machine_usize(this)?;
 409                 Self::check_alloc_request(new_size, align)?;
 410                 // No need to check old_size; we anyway check that they match the allocation.
 411                 let align = Align::from_bytes(align).unwrap();
 412                 let new_ptr = this.memory.reallocate(
 413                     ptr,
 414                     Some((Size::from_bytes(old_size), align)),
 415                     Size::from_bytes(new_size),
 416                     align,
 417                     MiriMemoryKind::Rust.into(),
 418                 )?;
 419                 this.write_scalar(new_ptr, dest)?;
 420             }
 421
 422             // C memory handling functions
 423             "memcmp" => {
 424                 check_abi(this, abi, Abi::C { unwind: false })?;
 425                 let &[ref left, ref right, ref n] = check_arg_count(args)?;
 426                 let left = this.read_scalar(left)?.check_init()?;
 427                 let right = this.read_scalar(right)?.check_init()?;
 428                 let n = Size::from_bytes(this.read_scalar(n)?.to_machine_usize(this)?);
 429
 430                 let result = {
 431                     let left_bytes = this.memory.read_bytes(left, n)?;
 432                     let right_bytes = this.memory.read_bytes(right, n)?;
 433
 434                     use std::cmp::Ordering::*;
 435                     match left_bytes.cmp(right_bytes) {
 436                         Less => -1i32,
 437                         Equal => 0,
 438                         Greater => 1,
 439                     }
 440                 };
 441
 442                 this.write_scalar(Scalar::from_i32(result), dest)?;
 443             }
 444             "memrchr" => {
 445                 check_abi(this, abi, Abi::C { unwind: false })?;
 446                 let &[ref ptr, ref val, ref num] = check_arg_count(args)?;
 447                 let ptr = this.read_scalar(ptr)?.check_init()?;
 448                 let val = this.read_scalar(val)?.to_i32()? as u8;
 449                 let num = this.read_scalar(num)?.to_machine_usize(this)?;
 450                 if let Some(idx) = this
 451                     .memory
 452                     .read_bytes(ptr, Size::from_bytes(num))?
 453                     .iter()
 454                     .rev()
 455                     .position(|&c| c == val)
 456                 {
 457                     let new_ptr = ptr.ptr_offset(Size::from_bytes(num - idx as u64 - 1), this)?;
 458                     this.write_scalar(new_ptr, dest)?;
 459                 } else {
 460                     this.write_null(dest)?;
 461                 }
 462             }
 463             "memchr" => {
 464                 check_abi(this, abi, Abi::C { unwind: false })?;
 465                 let &[ref ptr, ref val, ref num] = check_arg_count(args)?;
 466                 let ptr = this.read_scalar(ptr)?.check_init()?;
 467                 let val = this.read_scalar(val)?.to_i32()? as u8;
 468                 let num = this.read_scalar(num)?.to_machine_usize(this)?;
 469                 let idx = this
 470                     .memory
 471                     .read_bytes(ptr, Size::from_bytes(num))?
 472                     .iter()
 473                     .position(|&c| c == val);
 474                 if let Some(idx) = idx {
 475                     let new_ptr = ptr.ptr_offset(Size::from_bytes(idx as u64), this)?;
 476                     this.write_scalar(new_ptr, dest)?;
 477                 } else {
 478                     this.write_null(dest)?;
 479                 }
 480             }
 481             "strlen" => {
 482                 check_abi(this, abi, Abi::C { unwind: false })?;
 483                 let &[ref ptr] = check_arg_count(args)?;
 484                 let ptr = this.read_scalar(ptr)?.check_init()?;
 485                 let n = this.read_c_str(ptr)?.len();
 486                 this.write_scalar(Scalar::from_machine_usize(u64::try_from(n).unwrap(), this), dest)?;
 487             }
 488
 489             // math functions
 490             #[rustfmt::skip]
 491             | "cbrtf"
 492             | "coshf"
 493             | "sinhf"
 494             | "tanf"
 495             | "acosf"
 496             | "asinf"
 497             | "atanf"
 498             => {
 499                 check_abi(this, abi, Abi::C { unwind: false })?;
 500                 let &[ref f] = check_arg_count(args)?;
 501                 // FIXME: Using host floats.
 502                 let f = f32::from_bits(this.read_scalar(f)?.to_u32()?);
 503                 let f = match link_name {
 504                     "cbrtf" => f.cbrt(),
 505                     "coshf" => f.cosh(),
 506                     "sinhf" => f.sinh(),
 507                     "tanf" => f.tan(),
 508                     "acosf" => f.acos(),
 509                     "asinf" => f.asin(),
 510                     "atanf" => f.atan(),
 511                     _ => bug!(),
 512                 };
 513                 this.write_scalar(Scalar::from_u32(f.to_bits()), dest)?;
 514             }
 515             #[rustfmt::skip]
 516             | "_hypotf"
 517             | "hypotf"
 518             | "atan2f"
 519             => {
 520                 check_abi(this, abi, Abi::C { unwind: false })?;
 521                 let &[ref f1, ref f2] = check_arg_count(args)?;
 522                 // underscore case for windows, here and below
 523                 // (see https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/floating-point-primitives?view=vs-2019)
 524                 // FIXME: Using host floats.
 525                 let f1 = f32::from_bits(this.read_scalar(f1)?.to_u32()?);
 526                 let f2 = f32::from_bits(this.read_scalar(f2)?.to_u32()?);
 527                 let n = match link_name {
 528                     "_hypotf" | "hypotf" => f1.hypot(f2),
 529                     "atan2f" => f1.atan2(f2),
 530                     _ => bug!(),
 531                 };
 532                 this.write_scalar(Scalar::from_u32(n.to_bits()), dest)?;
 533             }
 534             #[rustfmt::skip]
 535             | "cbrt"
 536             | "cosh"
 537             | "sinh"
 538             | "tan"
 539             | "acos"
 540             | "asin"
 541             | "atan"
 542             => {
 543                 check_abi(this, abi, Abi::C { unwind: false })?;
 544                 let &[ref f] = check_arg_count(args)?;
 545                 // FIXME: Using host floats.
 546                 let f = f64::from_bits(this.read_scalar(f)?.to_u64()?);
 547                 let f = match link_name {
 548                     "cbrt" => f.cbrt(),
 549                     "cosh" => f.cosh(),
 550                     "sinh" => f.sinh(),
 551                     "tan" => f.tan(),
 552                     "acos" => f.acos(),
 553                     "asin" => f.asin(),
 554                     "atan" => f.atan(),
 555                     _ => bug!(),
 556                 };
 557                 this.write_scalar(Scalar::from_u64(f.to_bits()), dest)?;
 558             }
 559             #[rustfmt::skip]
 560             | "_hypot"
 561             | "hypot"
 562             | "atan2"
 563             => {
 564                 check_abi(this, abi, Abi::C { unwind: false })?;
 565                 let &[ref f1, ref f2] = check_arg_count(args)?;
 566                 // FIXME: Using host floats.
 567                 let f1 = f64::from_bits(this.read_scalar(f1)?.to_u64()?);
 568                 let f2 = f64::from_bits(this.read_scalar(f2)?.to_u64()?);
 569                 let n = match link_name {
 570                     "_hypot" | "hypot" => f1.hypot(f2),
 571                     "atan2" => f1.atan2(f2),
 572                     _ => bug!(),
 573                 };
 574                 this.write_scalar(Scalar::from_u64(n.to_bits()), dest)?;
 575             }
 576             #[rustfmt::skip]
 577             | "_ldexp"
 578             | "ldexp"
 579             | "scalbn"
 580             => {
 581                 check_abi(this, abi, Abi::C { unwind: false })?;
 582                 let &[ref x, ref exp] = check_arg_count(args)?;
 583                 // For radix-2 (binary) systems, `ldexp` and `scalbn` are the same.
 584                 let x = this.read_scalar(x)?.to_f64()?;
 585                 let exp = this.read_scalar(exp)?.to_i32()?;
 586
 587                 // Saturating cast to i16. Even those are outside the valid exponent range to
 588                 // `scalbn` below will do its over/underflow handling.
 589                 let exp = if exp > i32::from(i16::MAX) {
 590                     i16::MAX
 591                 } else if exp < i32::from(i16::MIN) {
 592                     i16::MIN
 593                 } else {
 594                     exp.try_into().unwrap()
 595                 };
 596
 597                 let res = x.scalbn(exp);
 598                 this.write_scalar(Scalar::from_f64(res), dest)?;
 599             }
 600
 601             // Architecture-specific shims
 602             "llvm.x86.sse2.pause" if this.tcx.sess.target.arch == "x86" || this.tcx.sess.target.arch == "x86_64" => {
 603                 check_abi(this, abi, Abi::C { unwind: false })?;
 604                 let &[] = check_arg_count(args)?;
 605                 this.yield_active_thread();
 606             }
 607             "llvm.aarch64.isb" if this.tcx.sess.target.arch == "aarch64" => {
 608                 check_abi(this, abi, Abi::C { unwind: false })?;
 609                 let &[ref arg] = check_arg_count(args)?;
 610                 let arg = this.read_scalar(arg)?.to_i32()?;
 611                 match arg {
 612                     15 => { // SY ("full system scope")
 613                         this.yield_active_thread();
 614                     }
 615                     _ => {
 616                         throw_unsup_format!("unsupported llvm.aarch64.isb argument {}", arg);
 617                     }
 618                 }
 619             }
 620
 621             // Platform-specific shims
 622             _ => match this.tcx.sess.target.os.as_str() {
 623                 "linux" | "macos" => return shims::posix::foreign_items::EvalContextExt::emulate_foreign_item_by_name(this, link_name, abi, args, dest, ret),
 624                 "windows" => return shims::windows::foreign_items::EvalContextExt::emulate_foreign_item_by_name(this, link_name, abi, args, dest, ret),
 625                 target => throw_unsup_format!("the target `{}` is not supported", target),
 626             }
 627         };
 628
 629         // We only fall through to here if we did *not* hit the `_` arm above,
 630         // i.e., if we actually emulated the function.
 631         Ok(EmulateByNameResult::NeedsJumping)
 632     }
 633
 634     /// Check some basic requirements for this allocation request:
 635     /// non-zero size, power-of-two alignment.
 636     fn check_alloc_request(size: u64, align: u64) -> InterpResult<'tcx> {
 637         if size == 0 {
 638             throw_ub_format!("creating allocation with size 0");
 639         }
 640         if !align.is_power_of_two() {
 641             throw_ub_format!("creating allocation with non-power-of-two alignment {}", align);
 642         }
 643         Ok(())
 644     }
 645 }