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