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