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