src/tools/miri/src/shims/foreign_items.rs

   1 use std::{collections::hash_map::Entry, iter};
   2
   3 use log::trace;
   4
   5 use rustc_apfloat::Float;
   6 use rustc_ast::expand::allocator::AllocatorKind;
   7 use rustc_hir::{
   8     def::DefKind,
   9     def_id::{CrateNum, DefId, LOCAL_CRATE},
  10 };
  11 use rustc_middle::middle::{
  12     codegen_fn_attrs::CodegenFnAttrFlags, dependency_format::Linkage,
  13     exported_symbols::ExportedSymbol,
  14 };
  15 use rustc_middle::mir;
  16 use rustc_middle::ty;
  17 use rustc_session::config::CrateType;
  18 use rustc_span::Symbol;
  19 use rustc_target::{
  20     abi::{Align, Size},
  21     spec::abi::Abi,
  22 };
  23
  24 use super::backtrace::EvalContextExt as _;
  25 use crate::helpers::{convert::Truncate, target_os_is_unix};
  26 #[cfg(unix)]
  27 use crate::shims::ffi_support::EvalContextExt as _;
  28 use crate::*;
  29
  30 /// Returned by `emulate_foreign_item_by_name`.
  31 pub enum EmulateByNameResult<'mir, 'tcx> {
  32     /// The caller is expected to jump to the return block.
  33     NeedsJumping,
  34     /// Jumping has already been taken care of.
  35     AlreadyJumped,
  36     /// A MIR body has been found for the function.
  37     MirBody(&'mir mir::Body<'tcx>, ty::Instance<'tcx>),
  38     /// The item is not supported.
  39     NotSupported,
  40 }
  41
  42 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriInterpCx<'mir, 'tcx> {}
  43 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
  44     /// Returns the minimum alignment for the target architecture for allocations of the given size.
  45     fn min_align(&self, size: u64, kind: MiriMemoryKind) -> Align {
  46         let this = self.eval_context_ref();
  47         // List taken from `library/std/src/sys/common/alloc.rs`.
  48         // This list should be kept in sync with the one from libstd.
  49         let min_align = match this.tcx.sess.target.arch.as_ref() {
  50             "x86" | "arm" | "mips" | "powerpc" | "powerpc64" | "asmjs" | "wasm32" => 8,
  51             "x86_64" | "aarch64" | "mips64" | "s390x" | "sparc64" => 16,
  52             arch => bug!("Unsupported target architecture: {}", arch),
  53         };
  54         // Windows always aligns, even small allocations.
  55         // Source: <https://support.microsoft.com/en-us/help/286470/how-to-use-pageheap-exe-in-windows-xp-windows-2000-and-windows-server>
  56         // But jemalloc does not, so for the C heap we only align if the allocation is sufficiently big.
  57         if kind == MiriMemoryKind::WinHeap || size >= min_align {
  58             return Align::from_bytes(min_align).unwrap();
  59         }
  60         // We have `size < min_align`. Round `size` *down* to the next power of two and use that.
  61         fn prev_power_of_two(x: u64) -> u64 {
  62             let next_pow2 = x.next_power_of_two();
  63             if next_pow2 == x {
  64                 // x *is* a power of two, just use that.
  65                 x
  66             } else {
  67                 // x is between two powers, so next = 2*prev.
  68                 next_pow2 / 2
  69             }
  70         }
  71         Align::from_bytes(prev_power_of_two(size)).unwrap()
  72     }
  73
  74     fn malloc(
  75         &mut self,
  76         size: u64,
  77         zero_init: bool,
  78         kind: MiriMemoryKind,
  79     ) -> InterpResult<'tcx, Pointer<Option<Provenance>>> {
  80         let this = self.eval_context_mut();
  81         if size == 0 {
  82             Ok(Pointer::null())
  83         } else {
  84             let align = this.min_align(size, kind);
  85             let ptr = this.allocate_ptr(Size::from_bytes(size), align, kind.into())?;
  86             if zero_init {
  87                 // We just allocated this, the access is definitely in-bounds and fits into our address space.
  88                 this.write_bytes_ptr(
  89                     ptr.into(),
  90                     iter::repeat(0u8).take(usize::try_from(size).unwrap()),
  91                 )
  92                 .unwrap();
  93             }
  94             Ok(ptr.into())
  95         }
  96     }
  97
  98     fn free(
  99         &mut self,
 100         ptr: Pointer<Option<Provenance>>,
 101         kind: MiriMemoryKind,
 102     ) -> InterpResult<'tcx> {
 103         let this = self.eval_context_mut();
 104         if !this.ptr_is_null(ptr)? {
 105             this.deallocate_ptr(ptr, None, kind.into())?;
 106         }
 107         Ok(())
 108     }
 109
 110     fn realloc(
 111         &mut self,
 112         old_ptr: Pointer<Option<Provenance>>,
 113         new_size: u64,
 114         kind: MiriMemoryKind,
 115     ) -> InterpResult<'tcx, Pointer<Option<Provenance>>> {
 116         let this = self.eval_context_mut();
 117         let new_align = this.min_align(new_size, kind);
 118         if this.ptr_is_null(old_ptr)? {
 119             if new_size == 0 {
 120                 Ok(Pointer::null())
 121             } else {
 122                 let new_ptr =
 123                     this.allocate_ptr(Size::from_bytes(new_size), new_align, kind.into())?;
 124                 Ok(new_ptr.into())
 125             }
 126         } else {
 127             if new_size == 0 {
 128                 this.deallocate_ptr(old_ptr, None, kind.into())?;
 129                 Ok(Pointer::null())
 130             } else {
 131                 let new_ptr = this.reallocate_ptr(
 132                     old_ptr,
 133                     None,
 134                     Size::from_bytes(new_size),
 135                     new_align,
 136                     kind.into(),
 137                 )?;
 138                 Ok(new_ptr.into())
 139             }
 140         }
 141     }
 142
 143     /// Lookup the body of a function that has `link_name` as the symbol name.
 144     fn lookup_exported_symbol(
 145         &mut self,
 146         link_name: Symbol,
 147     ) -> InterpResult<'tcx, Option<(&'mir mir::Body<'tcx>, ty::Instance<'tcx>)>> {
 148         let this = self.eval_context_mut();
 149         let tcx = this.tcx.tcx;
 150
 151         // If the result was cached, just return it.
 152         // (Cannot use `or_insert` since the code below might have to throw an error.)
 153         let entry = this.machine.exported_symbols_cache.entry(link_name);
 154         let instance = *match entry {
 155             Entry::Occupied(e) => e.into_mut(),
 156             Entry::Vacant(e) => {
 157                 // Find it if it was not cached.
 158                 let mut instance_and_crate: Option<(ty::Instance<'_>, CrateNum)> = None;
 159                 // `dependency_formats` includes all the transitive informations needed to link a crate,
 160                 // which is what we need here since we need to dig out `exported_symbols` from all transitive
 161                 // dependencies.
 162                 let dependency_formats = tcx.dependency_formats(());
 163                 let dependency_format = dependency_formats
 164                     .iter()
 165                     .find(|(crate_type, _)| *crate_type == CrateType::Executable)
 166                     .expect("interpreting a non-executable crate");
 167                 for cnum in iter::once(LOCAL_CRATE).chain(
 168                     dependency_format.1.iter().enumerate().filter_map(|(num, &linkage)| {
 169                         // We add 1 to the number because that's what rustc also does everywhere it
 170                         // calls `CrateNum::new`...
 171                         #[allow(clippy::integer_arithmetic)]
 172                         (linkage != Linkage::NotLinked).then_some(CrateNum::new(num + 1))
 173                     }),
 174                 ) {
 175                     // We can ignore `_export_info` here: we are a Rust crate, and everything is exported
 176                     // from a Rust crate.
 177                     for &(symbol, _export_info) in tcx.exported_symbols(cnum) {
 178                         if let ExportedSymbol::NonGeneric(def_id) = symbol {
 179                             let attrs = tcx.codegen_fn_attrs(def_id);
 180                             let symbol_name = if let Some(export_name) = attrs.export_name {
 181                                 export_name
 182                             } else if attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE) {
 183                                 tcx.item_name(def_id)
 184                             } else {
 185                                 // Skip over items without an explicitly defined symbol name.
 186                                 continue;
 187                             };
 188                             if symbol_name == link_name {
 189                                 if let Some((original_instance, original_cnum)) = instance_and_crate
 190                                 {
 191                                     // Make sure we are consistent wrt what is 'first' and 'second'.
 192                                     let original_span =
 193                                         tcx.def_span(original_instance.def_id()).data();
 194                                     let span = tcx.def_span(def_id).data();
 195                                     if original_span < span {
 196                                         throw_machine_stop!(
 197                                             TerminationInfo::MultipleSymbolDefinitions {
 198                                                 link_name,
 199                                                 first: original_span,
 200                                                 first_crate: tcx.crate_name(original_cnum),
 201                                                 second: span,
 202                                                 second_crate: tcx.crate_name(cnum),
 203                                             }
 204                                         );
 205                                     } else {
 206                                         throw_machine_stop!(
 207                                             TerminationInfo::MultipleSymbolDefinitions {
 208                                                 link_name,
 209                                                 first: span,
 210                                                 first_crate: tcx.crate_name(cnum),
 211                                                 second: original_span,
 212                                                 second_crate: tcx.crate_name(original_cnum),
 213                                             }
 214                                         );
 215                                     }
 216                                 }
 217                                 if !matches!(tcx.def_kind(def_id), DefKind::Fn | DefKind::AssocFn) {
 218                                     throw_ub_format!(
 219                                         "attempt to call an exported symbol that is not defined as a function"
 220                                     );
 221                                 }
 222                                 instance_and_crate = Some((ty::Instance::mono(tcx, def_id), cnum));
 223                             }
 224                         }
 225                     }
 226                 }
 227
 228                 e.insert(instance_and_crate.map(|ic| ic.0))
 229             }
 230         };
 231         match instance {
 232             None => Ok(None), // no symbol with this name
 233             Some(instance) => Ok(Some((this.load_mir(instance.def, None)?, instance))),
 234         }
 235     }
 236
 237     /// Emulates calling a foreign item, failing if the item is not supported.
 238     /// This function will handle `goto_block` if needed.
 239     /// Returns Ok(None) if the foreign item was completely handled
 240     /// by this function.
 241     /// Returns Ok(Some(body)) if processing the foreign item
 242     /// is delegated to another function.
 243     fn emulate_foreign_item(
 244         &mut self,
 245         def_id: DefId,
 246         abi: Abi,
 247         args: &[OpTy<'tcx, Provenance>],
 248         dest: &PlaceTy<'tcx, Provenance>,
 249         ret: Option<mir::BasicBlock>,
 250         unwind: StackPopUnwind,
 251     ) -> InterpResult<'tcx, Option<(&'mir mir::Body<'tcx>, ty::Instance<'tcx>)>> {
 252         let this = self.eval_context_mut();
 253         let link_name = this.item_link_name(def_id);
 254         let tcx = this.tcx.tcx;
 255
 256         // First: functions that diverge.
 257         let ret = match ret {
 258             None =>
 259                 match link_name.as_str() {
 260                     "miri_start_panic" => {
 261                         // `check_shim` happens inside `handle_miri_start_panic`.
 262                         this.handle_miri_start_panic(abi, link_name, args, unwind)?;
 263                         return Ok(None);
 264                     }
 265                     // This matches calls to the foreign item `panic_impl`.
 266                     // The implementation is provided by the function with the `#[panic_handler]` attribute.
 267                     "panic_impl" => {
 268                         // We don't use `check_shim` here because we are just forwarding to the lang
 269                         // item. Argument count checking will be performed when the returned `Body` is
 270                         // called.
 271                         this.check_abi_and_shim_symbol_clash(abi, Abi::Rust, link_name)?;
 272                         let panic_impl_id = tcx.lang_items().panic_impl().unwrap();
 273                         let panic_impl_instance = ty::Instance::mono(tcx, panic_impl_id);
 274                         return Ok(Some((
 275                             this.load_mir(panic_impl_instance.def, None)?,
 276                             panic_impl_instance,
 277                         )));
 278                     }
 279                     #[rustfmt::skip]
 280                     | "exit"
 281                     | "ExitProcess"
 282                     => {
 283                         let exp_abi = if link_name.as_str() == "exit" {
 284                             Abi::C { unwind: false }
 285                         } else {
 286                             Abi::System { unwind: false }
 287                         };
 288                         let [code] = this.check_shim(abi, exp_abi, link_name, args)?;
 289                         // it's really u32 for ExitProcess, but we have to put it into the `Exit` variant anyway
 290                         let code = this.read_scalar(code)?.to_i32()?;
 291                         throw_machine_stop!(TerminationInfo::Exit(code.into()));
 292                     }
 293                     "abort" => {
 294                         let [] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 295                         throw_machine_stop!(TerminationInfo::Abort(
 296                             "the program aborted execution".to_owned()
 297                         ))
 298                     }
 299                     _ => {
 300                         if let Some(body) = this.lookup_exported_symbol(link_name)? {
 301                             return Ok(Some(body));
 302                         }
 303                         this.handle_unsupported(format!(
 304                             "can't call (diverging) foreign function: {}",
 305                             link_name
 306                         ))?;
 307                         return Ok(None);
 308                     }
 309                 },
 310             Some(p) => p,
 311         };
 312
 313         // Second: functions that return immediately.
 314         match this.emulate_foreign_item_by_name(link_name, abi, args, dest)? {
 315             EmulateByNameResult::NeedsJumping => {
 316                 trace!("{:?}", this.dump_place(**dest));
 317                 this.go_to_block(ret);
 318             }
 319             EmulateByNameResult::AlreadyJumped => (),
 320             EmulateByNameResult::MirBody(mir, instance) => return Ok(Some((mir, instance))),
 321             EmulateByNameResult::NotSupported => {
 322                 if let Some(body) = this.lookup_exported_symbol(link_name)? {
 323                     return Ok(Some(body));
 324                 }
 325
 326                 this.handle_unsupported(format!("can't call foreign function: {}", link_name))?;
 327                 return Ok(None);
 328             }
 329         }
 330
 331         Ok(None)
 332     }
 333
 334     /// Emulates calling the internal __rust_* allocator functions
 335     fn emulate_allocator(
 336         &mut self,
 337         symbol: Symbol,
 338         default: impl FnOnce(&mut MiriInterpCx<'mir, 'tcx>) -> InterpResult<'tcx>,
 339     ) -> InterpResult<'tcx, EmulateByNameResult<'mir, 'tcx>> {
 340         let this = self.eval_context_mut();
 341
 342         let allocator_kind = if let Some(allocator_kind) = this.tcx.allocator_kind(()) {
 343             allocator_kind
 344         } else {
 345             // in real code, this symbol does not exist without an allocator
 346             return Ok(EmulateByNameResult::NotSupported);
 347         };
 348
 349         match allocator_kind {
 350             AllocatorKind::Global => {
 351                 let (body, instance) = this
 352                     .lookup_exported_symbol(symbol)?
 353                     .expect("symbol should be present if there is a global allocator");
 354
 355                 Ok(EmulateByNameResult::MirBody(body, instance))
 356             }
 357             AllocatorKind::Default => {
 358                 default(this)?;
 359                 Ok(EmulateByNameResult::NeedsJumping)
 360             }
 361         }
 362     }
 363
 364     /// Emulates calling a foreign item using its name.
 365     fn emulate_foreign_item_by_name(
 366         &mut self,
 367         link_name: Symbol,
 368         abi: Abi,
 369         args: &[OpTy<'tcx, Provenance>],
 370         dest: &PlaceTy<'tcx, Provenance>,
 371     ) -> InterpResult<'tcx, EmulateByNameResult<'mir, 'tcx>> {
 372         let this = self.eval_context_mut();
 373
 374         // First deal with any external C functions in linked .so file.
 375         #[cfg(unix)]
 376         if this.machine.external_so_lib.as_ref().is_some() {
 377             // An Ok(false) here means that the function being called was not exported
 378             // by the specified `.so` file; we should continue and check if it corresponds to
 379             // a provided shim.
 380             if this.call_external_c_fct(link_name, dest, args)? {
 381                 return Ok(EmulateByNameResult::NeedsJumping);
 382             }
 383         }
 384
 385         // When adding a new shim, you should follow the following pattern:
 386         // ```
 387         // "shim_name" => {
 388         //     let [arg1, arg2, arg3] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 389         //     let result = this.shim_name(arg1, arg2, arg3)?;
 390         //     this.write_scalar(result, dest)?;
 391         // }
 392         // ```
 393         // and then define `shim_name` as a helper function in an extension trait in a suitable file
 394         // (see e.g. `unix/fs.rs`):
 395         // ```
 396         // fn shim_name(
 397         //     &mut self,
 398         //     arg1: &OpTy<'tcx, Provenance>,
 399         //     arg2: &OpTy<'tcx, Provenance>,
 400         //     arg3: &OpTy<'tcx, Provenance>)
 401         // -> InterpResult<'tcx, Scalar<Provenance>> {
 402         //     let this = self.eval_context_mut();
 403         //
 404         //     // First thing: load all the arguments. Details depend on the shim.
 405         //     let arg1 = this.read_scalar(arg1)?.to_u32()?;
 406         //     let arg2 = this.read_pointer(arg2)?; // when you need to work with the pointer directly
 407         //     let arg3 = this.deref_operand(arg3)?; // when you want to load/store through the pointer at its declared type
 408         //
 409         //     // ...
 410         //
 411         //     Ok(Scalar::from_u32(42))
 412         // }
 413         // ```
 414         // You might find existing shims not following this pattern, most
 415         // likely because they predate it or because for some reason they cannot be made to fit.
 416
 417         // Here we dispatch all the shims for foreign functions. If you have a platform specific
 418         // shim, add it to the corresponding submodule.
 419         match link_name.as_str() {
 420             // Miri-specific extern functions
 421             "miri_static_root" => {
 422                 let [ptr] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 423                 let ptr = this.read_pointer(ptr)?;
 424                 let (alloc_id, offset, _) = this.ptr_get_alloc_id(ptr)?;
 425                 if offset != Size::ZERO {
 426                     throw_unsup_format!("pointer passed to miri_static_root must point to beginning of an allocated block");
 427                 }
 428                 this.machine.static_roots.push(alloc_id);
 429             }
 430
 431             // Obtains the size of a Miri backtrace. See the README for details.
 432             "miri_backtrace_size" => {
 433                 this.handle_miri_backtrace_size(abi, link_name, args, dest)?;
 434             }
 435
 436             // Obtains a Miri backtrace. See the README for details.
 437             "miri_get_backtrace" => {
 438                 // `check_shim` happens inside `handle_miri_get_backtrace`.
 439                 this.handle_miri_get_backtrace(abi, link_name, args, dest)?;
 440             }
 441
 442             // Resolves a Miri backtrace frame. See the README for details.
 443             "miri_resolve_frame" => {
 444                 // `check_shim` happens inside `handle_miri_resolve_frame`.
 445                 this.handle_miri_resolve_frame(abi, link_name, args, dest)?;
 446             }
 447
 448             // Writes the function and file names of a Miri backtrace frame into a user provided buffer. See the README for details.
 449             "miri_resolve_frame_names" => {
 450                 this.handle_miri_resolve_frame_names(abi, link_name, args)?;
 451             }
 452
 453             // Standard C allocation
 454             "malloc" => {
 455                 let [size] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 456                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
 457                 let res = this.malloc(size, /*zero_init:*/ false, MiriMemoryKind::C)?;
 458                 this.write_pointer(res, dest)?;
 459             }
 460             "calloc" => {
 461                 let [items, len] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 462                 let items = this.read_scalar(items)?.to_machine_usize(this)?;
 463                 let len = this.read_scalar(len)?.to_machine_usize(this)?;
 464                 let size =
 465                     items.checked_mul(len).ok_or_else(|| err_ub_format!("overflow during calloc size computation"))?;
 466                 let res = this.malloc(size, /*zero_init:*/ true, MiriMemoryKind::C)?;
 467                 this.write_pointer(res, dest)?;
 468             }
 469             "free" => {
 470                 let [ptr] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 471                 let ptr = this.read_pointer(ptr)?;
 472                 this.free(ptr, MiriMemoryKind::C)?;
 473             }
 474             "realloc" => {
 475                 let [old_ptr, new_size] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 476                 let old_ptr = this.read_pointer(old_ptr)?;
 477                 let new_size = this.read_scalar(new_size)?.to_machine_usize(this)?;
 478                 let res = this.realloc(old_ptr, new_size, MiriMemoryKind::C)?;
 479                 this.write_pointer(res, dest)?;
 480             }
 481
 482             // Rust allocation
 483             "__rust_alloc" => {
 484                 let [size, align] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 485                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
 486                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 487
 488                 return this.emulate_allocator(Symbol::intern("__rg_alloc"), |this| {
 489                     Self::check_alloc_request(size, align)?;
 490
 491                     let ptr = this.allocate_ptr(
 492                         Size::from_bytes(size),
 493                         Align::from_bytes(align).unwrap(),
 494                         MiriMemoryKind::Rust.into(),
 495                     )?;
 496
 497                     this.write_pointer(ptr, dest)
 498                 });
 499             }
 500             "__rust_alloc_zeroed" => {
 501                 let [size, align] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 502                 let size = this.read_scalar(size)?.to_machine_usize(this)?;
 503                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 504
 505                 return this.emulate_allocator(Symbol::intern("__rg_alloc_zeroed"), |this| {
 506                     Self::check_alloc_request(size, align)?;
 507
 508                     let ptr = this.allocate_ptr(
 509                         Size::from_bytes(size),
 510                         Align::from_bytes(align).unwrap(),
 511                         MiriMemoryKind::Rust.into(),
 512                     )?;
 513
 514                     // We just allocated this, the access is definitely in-bounds.
 515                     this.write_bytes_ptr(ptr.into(), iter::repeat(0u8).take(usize::try_from(size).unwrap())).unwrap();
 516                     this.write_pointer(ptr, dest)
 517                 });
 518             }
 519             "__rust_dealloc" => {
 520                 let [ptr, old_size, align] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 521                 let ptr = this.read_pointer(ptr)?;
 522                 let old_size = this.read_scalar(old_size)?.to_machine_usize(this)?;
 523                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 524
 525                 return this.emulate_allocator(Symbol::intern("__rg_dealloc"), |this| {
 526                     // No need to check old_size/align; we anyway check that they match the allocation.
 527                     this.deallocate_ptr(
 528                         ptr,
 529                         Some((Size::from_bytes(old_size), Align::from_bytes(align).unwrap())),
 530                         MiriMemoryKind::Rust.into(),
 531                     )
 532                 });
 533             }
 534             "__rust_realloc" => {
 535                 let [ptr, old_size, align, new_size] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 536                 let ptr = this.read_pointer(ptr)?;
 537                 let old_size = this.read_scalar(old_size)?.to_machine_usize(this)?;
 538                 let align = this.read_scalar(align)?.to_machine_usize(this)?;
 539                 let new_size = this.read_scalar(new_size)?.to_machine_usize(this)?;
 540                 // No need to check old_size; we anyway check that they match the allocation.
 541
 542                 return this.emulate_allocator(Symbol::intern("__rg_realloc"), |this| {
 543                     Self::check_alloc_request(new_size, align)?;
 544
 545                     let align = Align::from_bytes(align).unwrap();
 546                     let new_ptr = this.reallocate_ptr(
 547                         ptr,
 548                         Some((Size::from_bytes(old_size), align)),
 549                         Size::from_bytes(new_size),
 550                         align,
 551                         MiriMemoryKind::Rust.into(),
 552                     )?;
 553                     this.write_pointer(new_ptr, dest)
 554                 });
 555             }
 556
 557             // C memory handling functions
 558             "memcmp" => {
 559                 let [left, right, n] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 560                 let left = this.read_pointer(left)?;
 561                 let right = this.read_pointer(right)?;
 562                 let n = Size::from_bytes(this.read_scalar(n)?.to_machine_usize(this)?);
 563
 564                 let result = {
 565                     let left_bytes = this.read_bytes_ptr_strip_provenance(left, n)?;
 566                     let right_bytes = this.read_bytes_ptr_strip_provenance(right, n)?;
 567
 568                     use std::cmp::Ordering::*;
 569                     match left_bytes.cmp(right_bytes) {
 570                         Less => -1i32,
 571                         Equal => 0,
 572                         Greater => 1,
 573                     }
 574                 };
 575
 576                 this.write_scalar(Scalar::from_i32(result), dest)?;
 577             }
 578             "memrchr" => {
 579                 let [ptr, val, num] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 580                 let ptr = this.read_pointer(ptr)?;
 581                 let val = this.read_scalar(val)?.to_i32()?;
 582                 let num = this.read_scalar(num)?.to_machine_usize(this)?;
 583                 // The docs say val is "interpreted as unsigned char".
 584                 #[allow(clippy::cast_sign_loss, clippy::cast_possible_truncation)]
 585                 let val = val as u8;
 586
 587                 if let Some(idx) = this
 588                     .read_bytes_ptr_strip_provenance(ptr, Size::from_bytes(num))?
 589                     .iter()
 590                     .rev()
 591                     .position(|&c| c == val)
 592                 {
 593                     let idx = u64::try_from(idx).unwrap();
 594                     #[allow(clippy::integer_arithmetic)] // idx < num, so this never wraps
 595                     let new_ptr = ptr.offset(Size::from_bytes(num - idx - 1), this)?;
 596                     this.write_pointer(new_ptr, dest)?;
 597                 } else {
 598                     this.write_null(dest)?;
 599                 }
 600             }
 601             "memchr" => {
 602                 let [ptr, val, num] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 603                 let ptr = this.read_pointer(ptr)?;
 604                 let val = this.read_scalar(val)?.to_i32()?;
 605                 let num = this.read_scalar(num)?.to_machine_usize(this)?;
 606                 // The docs say val is "interpreted as unsigned char".
 607                 #[allow(clippy::cast_sign_loss, clippy::cast_possible_truncation)]
 608                 let val = val as u8;
 609
 610                 let idx = this
 611                     .read_bytes_ptr_strip_provenance(ptr, Size::from_bytes(num))?
 612                     .iter()
 613                     .position(|&c| c == val);
 614                 if let Some(idx) = idx {
 615                     let new_ptr = ptr.offset(Size::from_bytes(idx as u64), this)?;
 616                     this.write_pointer(new_ptr, dest)?;
 617                 } else {
 618                     this.write_null(dest)?;
 619                 }
 620             }
 621             "strlen" => {
 622                 let [ptr] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 623                 let ptr = this.read_pointer(ptr)?;
 624                 let n = this.read_c_str(ptr)?.len();
 625                 this.write_scalar(Scalar::from_machine_usize(u64::try_from(n).unwrap(), this), dest)?;
 626             }
 627
 628             // math functions (note that there are also intrinsics for some other functions)
 629             #[rustfmt::skip]
 630             | "cbrtf"
 631             | "coshf"
 632             | "sinhf"
 633             | "tanf"
 634             | "tanhf"
 635             | "acosf"
 636             | "asinf"
 637             | "atanf"
 638             | "log1pf"
 639             | "expm1f"
 640             => {
 641                 let [f] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 642                 // FIXME: Using host floats.
 643                 let f = f32::from_bits(this.read_scalar(f)?.to_u32()?);
 644                 let res = match link_name.as_str() {
 645                     "cbrtf" => f.cbrt(),
 646                     "coshf" => f.cosh(),
 647                     "sinhf" => f.sinh(),
 648                     "tanf" => f.tan(),
 649                     "tanhf" => f.tanh(),
 650                     "acosf" => f.acos(),
 651                     "asinf" => f.asin(),
 652                     "atanf" => f.atan(),
 653                     "log1pf" => f.ln_1p(),
 654                     "expm1f" => f.exp_m1(),
 655                     _ => bug!(),
 656                 };
 657                 this.write_scalar(Scalar::from_u32(res.to_bits()), dest)?;
 658             }
 659             #[rustfmt::skip]
 660             | "_hypotf"
 661             | "hypotf"
 662             | "atan2f"
 663             | "fdimf"
 664             => {
 665                 let [f1, f2] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 666                 // underscore case for windows, here and below
 667                 // (see https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/floating-point-primitives?view=vs-2019)
 668                 // FIXME: Using host floats.
 669                 let f1 = f32::from_bits(this.read_scalar(f1)?.to_u32()?);
 670                 let f2 = f32::from_bits(this.read_scalar(f2)?.to_u32()?);
 671                 let res = match link_name.as_str() {
 672                     "_hypotf" | "hypotf" => f1.hypot(f2),
 673                     "atan2f" => f1.atan2(f2),
 674                     #[allow(deprecated)]
 675                     "fdimf" => f1.abs_sub(f2),
 676                     _ => bug!(),
 677                 };
 678                 this.write_scalar(Scalar::from_u32(res.to_bits()), dest)?;
 679             }
 680             #[rustfmt::skip]
 681             | "cbrt"
 682             | "cosh"
 683             | "sinh"
 684             | "tan"
 685             | "tanh"
 686             | "acos"
 687             | "asin"
 688             | "atan"
 689             | "log1p"
 690             | "expm1"
 691             => {
 692                 let [f] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 693                 // FIXME: Using host floats.
 694                 let f = f64::from_bits(this.read_scalar(f)?.to_u64()?);
 695                 let res = match link_name.as_str() {
 696                     "cbrt" => f.cbrt(),
 697                     "cosh" => f.cosh(),
 698                     "sinh" => f.sinh(),
 699                     "tan" => f.tan(),
 700                     "tanh" => f.tanh(),
 701                     "acos" => f.acos(),
 702                     "asin" => f.asin(),
 703                     "atan" => f.atan(),
 704                     "log1p" => f.ln_1p(),
 705                     "expm1" => f.exp_m1(),
 706                     _ => bug!(),
 707                 };
 708                 this.write_scalar(Scalar::from_u64(res.to_bits()), dest)?;
 709             }
 710             #[rustfmt::skip]
 711             | "_hypot"
 712             | "hypot"
 713             | "atan2"
 714             | "fdim"
 715             => {
 716                 let [f1, f2] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 717                 // FIXME: Using host floats.
 718                 let f1 = f64::from_bits(this.read_scalar(f1)?.to_u64()?);
 719                 let f2 = f64::from_bits(this.read_scalar(f2)?.to_u64()?);
 720                 let res = match link_name.as_str() {
 721                     "_hypot" | "hypot" => f1.hypot(f2),
 722                     "atan2" => f1.atan2(f2),
 723                     #[allow(deprecated)]
 724                     "fdim" => f1.abs_sub(f2),
 725                     _ => bug!(),
 726                 };
 727                 this.write_scalar(Scalar::from_u64(res.to_bits()), dest)?;
 728             }
 729             #[rustfmt::skip]
 730             | "_ldexp"
 731             | "ldexp"
 732             | "scalbn"
 733             => {
 734                 let [x, exp] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 735                 // For radix-2 (binary) systems, `ldexp` and `scalbn` are the same.
 736                 let x = this.read_scalar(x)?.to_f64()?;
 737                 let exp = this.read_scalar(exp)?.to_i32()?;
 738
 739                 // Saturating cast to i16. Even those are outside the valid exponent range so
 740                 // `scalbn` below will do its over/underflow handling.
 741                 let exp = if exp > i32::from(i16::MAX) {
 742                     i16::MAX
 743                 } else if exp < i32::from(i16::MIN) {
 744                     i16::MIN
 745                 } else {
 746                     exp.try_into().unwrap()
 747                 };
 748
 749                 let res = x.scalbn(exp);
 750                 this.write_scalar(Scalar::from_f64(res), dest)?;
 751             }
 752
 753             // Architecture-specific shims
 754             "llvm.x86.addcarry.64" if this.tcx.sess.target.arch == "x86_64" => {
 755                 // Computes u8+u64+u64, returning tuple (u8,u64) comprising the output carry and truncated sum.
 756                 let [c_in, a, b] = this.check_shim(abi, Abi::Unadjusted, link_name, args)?;
 757                 let c_in = this.read_scalar(c_in)?.to_u8()?;
 758                 let a = this.read_scalar(a)?.to_u64()?;
 759                 let b = this.read_scalar(b)?.to_u64()?;
 760
 761                 #[allow(clippy::integer_arithmetic)] // adding two u64 and a u8 cannot wrap in a u128
 762                 let wide_sum = u128::from(c_in) + u128::from(a) + u128::from(b);
 763                 #[allow(clippy::integer_arithmetic)] // it's a u128, we can shift by 64
 764                 let (c_out, sum) = ((wide_sum >> 64).truncate::<u8>(), wide_sum.truncate::<u64>());
 765
 766                 let c_out_field = this.place_field(dest, 0)?;
 767                 this.write_scalar(Scalar::from_u8(c_out), &c_out_field)?;
 768                 let sum_field = this.place_field(dest, 1)?;
 769                 this.write_scalar(Scalar::from_u64(sum), &sum_field)?;
 770             }
 771             "llvm.x86.sse2.pause" if this.tcx.sess.target.arch == "x86" || this.tcx.sess.target.arch == "x86_64" => {
 772                 let [] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 773                 this.yield_active_thread();
 774             }
 775             "llvm.aarch64.isb" if this.tcx.sess.target.arch == "aarch64" => {
 776                 let [arg] = this.check_shim(abi, Abi::Unadjusted, link_name, args)?;
 777                 let arg = this.read_scalar(arg)?.to_i32()?;
 778                 match arg {
 779                     15 => { // SY ("full system scope")
 780                         this.yield_active_thread();
 781                     }
 782                     _ => {
 783                         throw_unsup_format!("unsupported llvm.aarch64.isb argument {}", arg);
 784                     }
 785                 }
 786             }
 787
 788             // Platform-specific shims
 789             _ => match this.tcx.sess.target.os.as_ref() {
 790                 target if target_os_is_unix(target) => return shims::unix::foreign_items::EvalContextExt::emulate_foreign_item_by_name(this, link_name, abi, args, dest),
 791                 "windows" => return shims::windows::foreign_items::EvalContextExt::emulate_foreign_item_by_name(this, link_name, abi, args, dest),
 792                 target => throw_unsup_format!("the target `{}` is not supported", target),
 793             }
 794         };
 795         // We only fall through to here if we did *not* hit the `_` arm above,
 796         // i.e., if we actually emulated the function with one of the shims.
 797         Ok(EmulateByNameResult::NeedsJumping)
 798     }
 799
 800     /// Check some basic requirements for this allocation request:
 801     /// non-zero size, power-of-two alignment.
 802     fn check_alloc_request(size: u64, align: u64) -> InterpResult<'tcx> {
 803         if size == 0 {
 804             throw_ub_format!("creating allocation with size 0");
 805         }
 806         if !align.is_power_of_two() {
 807             throw_ub_format!("creating allocation with non-power-of-two alignment {}", align);
 808         }
 809         Ok(())
 810     }
 811 }