src/shims/foreign_items.rs

   1 use std::{convert::{TryInto, TryFrom}, iter};
   2
   3 use log::trace;
   4
   5 use rustc_hir::def_id::DefId;
   6 use rustc_middle::mir;
   7 use rustc_target::{abi::{Align, Size}, spec::{PanicStrategy, abi::Abi}};
   8 use rustc_middle::ty;
   9 use rustc_apfloat::Float;
  10 use rustc_span::symbol::sym;
  11
  12 use crate::*;
  13 use super::backtrace::EvalContextExt as _;
  14 use helpers::{check_abi, check_arg_count};
  15
  16 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriEvalContext<'mir, 'tcx> {}
  17 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx> {
  18     /// Returns the minimum alignment for the target architecture for allocations of the given size.
  19     fn min_align(&self, size: u64, kind: MiriMemoryKind) -> Align {
  20         let this = self.eval_context_ref();
  21         // List taken from `libstd/sys_common/alloc.rs`.
  22         let min_align = match this.tcx.sess.target.arch.as_str() {
  23             "x86" | "arm" | "mips" | "powerpc" | "powerpc64" | "asmjs" | "wasm32" => 8,
  24             "x86_64" | "aarch64" | "mips64" | "s390x" | "sparc64" => 16,
  25             arch => bug!("Unsupported target architecture: {}", arch),
  26         };
  27         // Windows always aligns, even small allocations.
  28         // Source: <https://support.microsoft.com/en-us/help/286470/how-to-use-pageheap-exe-in-windows-xp-windows-2000-and-windows-server>
  29         // But jemalloc does not, so for the C heap we only align if the allocation is sufficiently big.
  30         if kind == MiriMemoryKind::WinHeap || size >= min_align {
  31             return Align::from_bytes(min_align).unwrap();
  32         }
  33         // We have `size < min_align`. Round `size` *down* to the next power of two and use that.
  34         fn prev_power_of_two(x: u64) -> u64 {
  35             let next_pow2 = x.next_power_of_two();
  36             if next_pow2 == x {
  37                 // x *is* a power of two, just use that.
  38                 x
  39             } else {
  40                 // x is between two powers, so next = 2*prev.
  41                 next_pow2 / 2
  42             }
  43         }
  44         Align::from_bytes(prev_power_of_two(size)).unwrap()
  45     }
  46
  47     fn malloc(&mut self, size: u64, zero_init: bool, kind: MiriMemoryKind) -> Scalar<Tag> {
  48         let this = self.eval_context_mut();
  49         if size == 0 {
  50             Scalar::null_ptr(this)
  51         } else {
  52             let align = this.min_align(size, kind);
  53             let ptr = this.memory.allocate(Size::from_bytes(size), align, kind.into());
  54             if zero_init {
  55                 // We just allocated this, the access is definitely in-bounds.
  56                 this.memory.write_bytes(ptr.into(), iter::repeat(0u8).take(size as usize)).unwrap();
  57             }
  58             Scalar::Ptr(ptr)
  59         }
  60     }
  61
  62     fn free(&mut self, ptr: Scalar<Tag>, kind: MiriMemoryKind) -> InterpResult<'tcx> {
  63         let this = self.eval_context_mut();
  64         if !this.is_null(ptr)? {
  65             let ptr = this.force_ptr(ptr)?;
  66             this.memory.deallocate(ptr, None, kind.into())?;
  67         }
  68         Ok(())
  69     }
  70
  71     fn realloc(
  72         &mut self,
  73         old_ptr: Scalar<Tag>,
  74         new_size: u64,
  75         kind: MiriMemoryKind,
  76     ) -> InterpResult<'tcx, Scalar<Tag>> {
  77         let this = self.eval_context_mut();
  78         let new_align = this.min_align(new_size, kind);
  79         if this.is_null(old_ptr)? {
  80             if new_size == 0 {
  81                 Ok(Scalar::null_ptr(this))
  82             } else {
  83                 let new_ptr =
  84                     this.memory.allocate(Size::from_bytes(new_size), new_align, kind.into());
  85                 Ok(Scalar::Ptr(new_ptr))
  86             }
  87         } else {
  88             let old_ptr = this.force_ptr(old_ptr)?;
  89             if new_size == 0 {
  90                 this.memory.deallocate(old_ptr, None, kind.into())?;
  91                 Ok(Scalar::null_ptr(this))
  92             } else {
  93                 let new_ptr = this.memory.reallocate(
  94                     old_ptr,
  95                     None,
  96                     Size::from_bytes(new_size),
  97                     new_align,
  98                     kind.into(),
  99                 )?;
 100                 Ok(Scalar::Ptr(new_ptr))
 101             }
 102         }
 103     }
 104
 105     /// Emulates calling a foreign item, failing if the item is not supported.
 106     /// This function will handle `goto_block` if needed.
 107     /// Returns Ok(None) if the foreign item was completely handled
 108     /// by this function.
 109     /// Returns Ok(Some(body)) if processing the foreign item
 110     /// is delegated to another function.
 111     #[rustfmt::skip]
 112     fn emulate_foreign_item(
 113         &mut self,
 114         def_id: DefId,
 115         abi: Abi,
 116         args: &[OpTy<'tcx, Tag>],
 117         ret: Option<(&PlaceTy<'tcx, Tag>, mir::BasicBlock)>,
 118         unwind: Option<mir::BasicBlock>,
 119     ) -> InterpResult<'tcx, Option<&'mir mir::Body<'tcx>>> {
 120         let this = self.eval_context_mut();
 121         let attrs = this.tcx.get_attrs(def_id);
 122         let link_name = match this.tcx.sess.first_attr_value_str_by_name(&attrs, sym::link_name) {
 123             Some(name) => name.as_str(),
 124             None => this.tcx.item_name(def_id).as_str(),
 125         };
 126         // Strip linker suffixes (seen on 32-bit macOS).
 127         let link_name = link_name.trim_end_matches("$UNIX2003");
 128         let tcx = this.tcx.tcx;
 129
 130         // First: functions that diverge.
 131         let (dest, ret) = match ret {
 132             None => match link_name {
 133                 "miri_start_panic" => {
 134                     check_abi(abi, Abi::Rust)?;
 135                     this.handle_miri_start_panic(args, unwind)?;
 136                     return Ok(None);
 137                 }
 138                 // This matches calls to the foreign item `panic_impl`.
 139                 // The implementation is provided by the function with the `#[panic_handler]` attribute.
 140                 "panic_impl" => {
 141                     check_abi(abi, Abi::Rust)?;
 142                     let panic_impl_id = tcx.lang_items().panic_impl().unwrap();
 143                     let panic_impl_instance = ty::Instance::mono(tcx, panic_impl_id);
 144                     return Ok(Some(&*this.load_mir(panic_impl_instance.def, None)?));
 145                 }
 146                 | "exit"
 147                 | "ExitProcess"
 148                 => {
 149                     check_abi(abi, if link_name == "exit" { Abi::C { unwind: false } } else { Abi::System { unwind: false } })?;
 150                     let &[ref code] = check_arg_count(args)?;
 151                     // it's really u32 for ExitProcess, but we have to put it into the `Exit` variant anyway
 152                     let code = this.read_scalar(code)?.to_i32()?;
 153                     throw_machine_stop!(TerminationInfo::Exit(code.into()));
 154                 }
 155                 "abort" => {
 156                     check_abi(abi, Abi::C { unwind: false })?;
 157                     throw_machine_stop!(TerminationInfo::Abort("the program aborted execution".to_owned()))
 158                 }
 159                 _ => throw_unsup_format!("can't call (diverging) foreign function: {}", link_name),
 160             },
 161             Some(p) => p,
 162         };
 163
 164         // Second: some functions that we forward to MIR implementations.
 165         match link_name {
 166             // This matches calls to the foreign item `__rust_start_panic`, that is,
 167             // calls to `extern "Rust" { fn __rust_start_panic(...) }`
 168             // (and `__rust_panic_cleanup`, respectively).
 169             // We forward this to the underlying *implementation* in the panic runtime crate.
 170             // Normally, this will be either `libpanic_unwind` or `libpanic_abort`, but it could
 171             // also be a custom user-provided implementation via `#![feature(panic_runtime)]`
 172             "__rust_start_panic" | "__rust_panic_cleanup" => {
 173                 check_abi(abi, Abi::C { unwind: false })?;
 174                 // This replicates some of the logic in `inject_panic_runtime`.
 175                 // FIXME: is there a way to reuse that logic?
 176                 let panic_runtime = match this.tcx.sess.panic_strategy() {
 177                     PanicStrategy::Unwind => sym::panic_unwind,
 178                     PanicStrategy::Abort => sym::panic_abort,
 179                 };
 180                 let start_panic_instance =
 181                     this.resolve_path(&[&*panic_runtime.as_str(), link_name]);
 182                 return Ok(Some(&*this.load_mir(start_panic_instance.def, None)?));
 183             }
 184             _ => {}
 185         }
 186
 187         // Third: functions that return.
 188         if this.emulate_foreign_item_by_name(link_name, abi, args, dest, ret)? {
 189             trace!("{:?}", this.dump_place(**dest));
 190             this.go_to_block(ret);
 191         }
 192
 193         Ok(None)
 194     }
 195
 196     /// Emulates calling a foreign item using its name, failing if the item is not supported.
 197     /// Returns `true` if the caller is expected to jump to the return block, and `false` if
 198     /// jumping has already been taken care of.
 199     fn emulate_foreign_item_by_name(
 200         &mut self,
 201         link_name: &str,
 202         abi: Abi,
 203         args: &[OpTy<'tcx, Tag>],
 204         dest: &PlaceTy<'tcx, Tag>,
 205         ret: mir::BasicBlock,
 206     ) -> InterpResult<'tcx, bool> {
 207         let this = self.eval_context_mut();
 208
 209         // Here we dispatch all the shims for foreign functions. If you have a platform specific
 210         // shim, add it to the corresponding submodule.
 211         match link_name {
 212             // Miri-specific extern functions
 213             "miri_static_root" => {
 214                 check_abi(abi, Abi::Rust)?;
 215                 let &[ref ptr] = check_arg_count(args)?;
 216                 let ptr = this.read_scalar(ptr)?.check_init()?;
 217                 let ptr = this.force_ptr(ptr)?;
 218                 if ptr.offset != Size::ZERO {
 219                     throw_unsup_format!("pointer passed to miri_static_root must point to beginning of an allocated block");
 220                 }
 221                 this.machine.static_roots.push(ptr.alloc_id);
 222             }
 223
 224             // Obtains a Miri backtrace. See the README for details.
 225             "miri_get_backtrace" => {
 226                 check_abi(abi, Abi::Rust)?;
 227                 this.handle_miri_get_backtrace(args, dest)?;
 228             }
 229
 230             // Resolves a Miri backtrace frame. See the README for details.
 231             "miri_resolve_frame" => {
 232                 check_abi(abi, Abi::Rust)?;
 233                 this.handle_miri_resolve_frame(args, dest)?;
 234             }
 235
 236
 237             // Standard C allocation
 238             "malloc" => {
 239                 check_abi(abi, Abi::C { unwind: false })?;
 240                 let &[ref size] = check_arg_count(args)?;
 241                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
 242                 let res = this.malloc(size, /*zero_init:*/ false, MiriMemoryKind::C);
 243                 this.write_scalar(res, dest)?;
 244             }
 245             "calloc" => {
 246                 check_abi(abi, Abi::C { unwind: false })?;
 247                 let &[ref items, ref len] = check_arg_count(args)?;
 248                 let items = this.read_scalar(items)?.to_machine_usize(this)?;
 249                 let len = this.read_scalar(len)?.to_machine_usize(this)?;
 250                 let size =
 251                     items.checked_mul(len).ok_or_else(|| err_ub_format!("overflow during calloc size computation"))?;
 252                 let res = this.malloc(size, /*zero_init:*/ true, MiriMemoryKind::C);
 253                 this.write_scalar(res, dest)?;
 254             }
 255             "free" => {
 256                 check_abi(abi, Abi::C { unwind: false })?;
 257                 let &[ref ptr] = check_arg_count(args)?;
 258                 let ptr = this.read_scalar(ptr)?.check_init()?;
 259                 this.free(ptr, MiriMemoryKind::C)?;
 260             }
 261             "realloc" => {
 262                 check_abi(abi, Abi::C { unwind: false })?;
 263                 let &[ref old_ptr, ref new_size] = check_arg_count(args)?;
 264                 let old_ptr = this.read_scalar(old_ptr)?.check_init()?;
 265                 let new_size = this.read_scalar(new_size)?.to_machine_usize(this)?;
 266                 let res = this.realloc(old_ptr, new_size, MiriMemoryKind::C)?;
 267                 this.write_scalar(res, dest)?;
 268             }
 269
 270             // Rust allocation
 271             // (Usually these would be forwarded to to `#[global_allocator]`; we instead implement a generic
 272             // allocation that also checks that all conditions are met, such as not permitting zero-sized allocations.)
 273             "__rust_alloc" => {
 274                 check_abi(abi, Abi::Rust)?;
 275                 let &[ref size, ref align] = check_arg_count(args)?;
 276                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
 277                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 278                 Self::check_alloc_request(size, align)?;
 279                 let ptr = this.memory.allocate(
 280                     Size::from_bytes(size),
 281                     Align::from_bytes(align).unwrap(),
 282                     MiriMemoryKind::Rust.into(),
 283                 );
 284                 this.write_scalar(ptr, dest)?;
 285             }
 286             "__rust_alloc_zeroed" => {
 287                 check_abi(abi, Abi::Rust)?;
 288                 let &[ref size, ref align] = check_arg_count(args)?;
 289                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
 290                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 291                 Self::check_alloc_request(size, align)?;
 292                 let ptr = this.memory.allocate(
 293                     Size::from_bytes(size),
 294                     Align::from_bytes(align).unwrap(),
 295                     MiriMemoryKind::Rust.into(),
 296                 );
 297                 // We just allocated this, the access is definitely in-bounds.
 298                 this.memory.write_bytes(ptr.into(), iter::repeat(0u8).take(usize::try_from(size).unwrap())).unwrap();
 299                 this.write_scalar(ptr, dest)?;
 300             }
 301             "__rust_dealloc" => {
 302                 check_abi(abi, Abi::Rust)?;
 303                 let &[ref ptr, ref old_size, ref align] = check_arg_count(args)?;
 304                 let ptr = this.read_scalar(ptr)?.check_init()?;
 305                 let old_size = this.read_scalar(old_size)?.to_machine_usize(this)?;
 306                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 307                 // No need to check old_size/align; we anyway check that they match the allocation.
 308                 let ptr = this.force_ptr(ptr)?;
 309                 this.memory.deallocate(
 310                     ptr,
 311                     Some((Size::from_bytes(old_size), Align::from_bytes(align).unwrap())),
 312                     MiriMemoryKind::Rust.into(),
 313                 )?;
 314             }
 315             "__rust_realloc" => {
 316                 check_abi(abi, Abi::Rust)?;
 317                 let &[ref ptr, ref old_size, ref align, ref new_size] = check_arg_count(args)?;
 318                 let ptr = this.force_ptr(this.read_scalar(ptr)?.check_init()?)?;
 319                 let old_size = this.read_scalar(old_size)?.to_machine_usize(this)?;
 320                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 321                 let new_size = this.read_scalar(new_size)?.to_machine_usize(this)?;
 322                 Self::check_alloc_request(new_size, align)?;
 323                 // No need to check old_size; we anyway check that they match the allocation.
 324                 let align = Align::from_bytes(align).unwrap();
 325                 let new_ptr = this.memory.reallocate(
 326                     ptr,
 327                     Some((Size::from_bytes(old_size), align)),
 328                     Size::from_bytes(new_size),
 329                     align,
 330                     MiriMemoryKind::Rust.into(),
 331                 )?;
 332                 this.write_scalar(new_ptr, dest)?;
 333             }
 334
 335             // C memory handling functions
 336             "memcmp" => {
 337                 check_abi(abi, Abi::C { unwind: false })?;
 338                 let &[ref left, ref right, ref n] = check_arg_count(args)?;
 339                 let left = this.read_scalar(left)?.check_init()?;
 340                 let right = this.read_scalar(right)?.check_init()?;
 341                 let n = Size::from_bytes(this.read_scalar(n)?.to_machine_usize(this)?);
 342
 343                 let result = {
 344                     let left_bytes = this.memory.read_bytes(left, n)?;
 345                     let right_bytes = this.memory.read_bytes(right, n)?;
 346
 347                     use std::cmp::Ordering::*;
 348                     match left_bytes.cmp(right_bytes) {
 349                         Less => -1i32,
 350                         Equal => 0,
 351                         Greater => 1,
 352                     }
 353                 };
 354
 355                 this.write_scalar(Scalar::from_i32(result), dest)?;
 356             }
 357             "memrchr" => {
 358                 check_abi(abi, Abi::C { unwind: false })?;
 359                 let &[ref ptr, ref val, ref num] = check_arg_count(args)?;
 360                 let ptr = this.read_scalar(ptr)?.check_init()?;
 361                 let val = this.read_scalar(val)?.to_i32()? as u8;
 362                 let num = this.read_scalar(num)?.to_machine_usize(this)?;
 363                 if let Some(idx) = this
 364                     .memory
 365                     .read_bytes(ptr, Size::from_bytes(num))?
 366                     .iter()
 367                     .rev()
 368                     .position(|&c| c == val)
 369                 {
 370                     let new_ptr = ptr.ptr_offset(Size::from_bytes(num - idx as u64 - 1), this)?;
 371                     this.write_scalar(new_ptr, dest)?;
 372                 } else {
 373                     this.write_null(dest)?;
 374                 }
 375             }
 376             "memchr" => {
 377                 check_abi(abi, Abi::C { unwind: false })?;
 378                 let &[ref ptr, ref val, ref num] = check_arg_count(args)?;
 379                 let ptr = this.read_scalar(ptr)?.check_init()?;
 380                 let val = this.read_scalar(val)?.to_i32()? as u8;
 381                 let num = this.read_scalar(num)?.to_machine_usize(this)?;
 382                 let idx = this
 383                     .memory
 384                     .read_bytes(ptr, Size::from_bytes(num))?
 385                     .iter()
 386                     .position(|&c| c == val);
 387                 if let Some(idx) = idx {
 388                     let new_ptr = ptr.ptr_offset(Size::from_bytes(idx as u64), this)?;
 389                     this.write_scalar(new_ptr, dest)?;
 390                 } else {
 391                     this.write_null(dest)?;
 392                 }
 393             }
 394             "strlen" => {
 395                 check_abi(abi, Abi::C { unwind: false })?;
 396                 let &[ref ptr] = check_arg_count(args)?;
 397                 let ptr = this.read_scalar(ptr)?.check_init()?;
 398                 let n = this.memory.read_c_str(ptr)?.len();
 399                 this.write_scalar(Scalar::from_machine_usize(u64::try_from(n).unwrap(), this), dest)?;
 400             }
 401
 402             // math functions
 403             | "cbrtf"
 404             | "coshf"
 405             | "sinhf"
 406             | "tanf"
 407             | "acosf"
 408             | "asinf"
 409             | "atanf"
 410             => {
 411                 check_abi(abi, Abi::C { unwind: false })?;
 412                 let &[ref f] = check_arg_count(args)?;
 413                 // FIXME: Using host floats.
 414                 let f = f32::from_bits(this.read_scalar(f)?.to_u32()?);
 415                 let f = match link_name {
 416                     "cbrtf" => f.cbrt(),
 417                     "coshf" => f.cosh(),
 418                     "sinhf" => f.sinh(),
 419                     "tanf" => f.tan(),
 420                     "acosf" => f.acos(),
 421                     "asinf" => f.asin(),
 422                     "atanf" => f.atan(),
 423                     _ => bug!(),
 424                 };
 425                 this.write_scalar(Scalar::from_u32(f.to_bits()), dest)?;
 426             }
 427             | "_hypotf"
 428             | "hypotf"
 429             | "atan2f"
 430             => {
 431                 check_abi(abi, Abi::C { unwind: false })?;
 432                 let &[ref f1, ref f2] = check_arg_count(args)?;
 433                 // underscore case for windows, here and below
 434                 // (see https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/floating-point-primitives?view=vs-2019)
 435                 // FIXME: Using host floats.
 436                 let f1 = f32::from_bits(this.read_scalar(f1)?.to_u32()?);
 437                 let f2 = f32::from_bits(this.read_scalar(f2)?.to_u32()?);
 438                 let n = match link_name {
 439                     "_hypotf" | "hypotf" => f1.hypot(f2),
 440                     "atan2f" => f1.atan2(f2),
 441                     _ => bug!(),
 442                 };
 443                 this.write_scalar(Scalar::from_u32(n.to_bits()), dest)?;
 444             }
 445             | "cbrt"
 446             | "cosh"
 447             | "sinh"
 448             | "tan"
 449             | "acos"
 450             | "asin"
 451             | "atan"
 452             => {
 453                 check_abi(abi, Abi::C { unwind: false })?;
 454                 let &[ref f] = check_arg_count(args)?;
 455                 // FIXME: Using host floats.
 456                 let f = f64::from_bits(this.read_scalar(f)?.to_u64()?);
 457                 let f = match link_name {
 458                     "cbrt" => f.cbrt(),
 459                     "cosh" => f.cosh(),
 460                     "sinh" => f.sinh(),
 461                     "tan" => f.tan(),
 462                     "acos" => f.acos(),
 463                     "asin" => f.asin(),
 464                     "atan" => f.atan(),
 465                     _ => bug!(),
 466                 };
 467                 this.write_scalar(Scalar::from_u64(f.to_bits()), dest)?;
 468             }
 469             | "_hypot"
 470             | "hypot"
 471             | "atan2"
 472             => {
 473                 check_abi(abi, Abi::C { unwind: false })?;
 474                 let &[ref f1, ref f2] = check_arg_count(args)?;
 475                 // FIXME: Using host floats.
 476                 let f1 = f64::from_bits(this.read_scalar(f1)?.to_u64()?);
 477                 let f2 = f64::from_bits(this.read_scalar(f2)?.to_u64()?);
 478                 let n = match link_name {
 479                     "_hypot" | "hypot" => f1.hypot(f2),
 480                     "atan2" => f1.atan2(f2),
 481                     _ => bug!(),
 482                 };
 483                 this.write_scalar(Scalar::from_u64(n.to_bits()), dest)?;
 484             }
 485             | "_ldexp"
 486             | "ldexp"
 487             | "scalbn"
 488             => {
 489                 check_abi(abi, Abi::C { unwind: false })?;
 490                 let &[ref x, ref exp] = check_arg_count(args)?;
 491                 // For radix-2 (binary) systems, `ldexp` and `scalbn` are the same.
 492                 let x = this.read_scalar(x)?.to_f64()?;
 493                 let exp = this.read_scalar(exp)?.to_i32()?;
 494
 495                 // Saturating cast to i16. Even those are outside the valid exponent range to
 496                 // `scalbn` below will do its over/underflow handling.
 497                 let exp = if exp > i32::from(i16::MAX) {
 498                     i16::MAX
 499                 } else if exp < i32::from(i16::MIN) {
 500                     i16::MIN
 501                 } else {
 502                     exp.try_into().unwrap()
 503                 };
 504
 505                 let res = x.scalbn(exp);
 506                 this.write_scalar(Scalar::from_f64(res), dest)?;
 507             }
 508
 509             // Architecture-specific shims
 510             "llvm.x86.sse2.pause" if this.tcx.sess.target.arch == "x86" || this.tcx.sess.target.arch == "x86_64" => {
 511                 check_abi(abi, Abi::C { unwind: false })?;
 512                 let &[] = check_arg_count(args)?;
 513                 this.yield_active_thread();
 514             }
 515             "llvm.aarch64.isb" if this.tcx.sess.target.arch == "aarch64" => {
 516                 check_abi(abi, Abi::C { unwind: false })?;
 517                 let &[ref arg] = check_arg_count(args)?;
 518                 let arg = this.read_scalar(arg)?.to_i32()?;
 519                 match arg {
 520                     15 => { // SY ("full system scope")
 521                         this.yield_active_thread();
 522                     }
 523                     _ => {
 524                         throw_unsup_format!("unsupported llvm.aarch64.isb argument {}", arg);
 525                     }
 526                 }
 527             }
 528
 529             // Platform-specific shims
 530             _ => match this.tcx.sess.target.os.as_str() {
 531                 "linux" | "macos" => return shims::posix::foreign_items::EvalContextExt::emulate_foreign_item_by_name(this, link_name, abi, args, dest, ret),
 532                 "windows" => return shims::windows::foreign_items::EvalContextExt::emulate_foreign_item_by_name(this, link_name, abi, args, dest, ret),
 533                 target => throw_unsup_format!("the target `{}` is not supported", target),
 534             }
 535         };
 536
 537         Ok(true)
 538     }
 539
 540     /// Check some basic requirements for this allocation request:
 541     /// non-zero size, power-of-two alignment.
 542     fn check_alloc_request(size: u64, align: u64) -> InterpResult<'tcx> {
 543         if size == 0 {
 544             throw_ub_format!("creating allocation with size 0");
 545         }
 546         if !align.is_power_of_two() {
 547             throw_ub_format!("creating allocation with non-power-of-two alignment {}", align);
 548         }
 549         Ok(())
 550     }
 551 }