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

   1 use std::{collections::hash_map::Entry, io::Write, iter, path::Path};
   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 use crate::*;
  27
  28 /// Returned by `emulate_foreign_item_by_name`.
  29 pub enum EmulateByNameResult<'mir, 'tcx> {
  30     /// The caller is expected to jump to the return block.
  31     NeedsJumping,
  32     /// Jumping has already been taken care of.
  33     AlreadyJumped,
  34     /// A MIR body has been found for the function.
  35     MirBody(&'mir mir::Body<'tcx>, ty::Instance<'tcx>),
  36     /// The item is not supported.
  37     NotSupported,
  38 }
  39
  40 impl<'mir, 'tcx: 'mir> EvalContextExt<'mir, 'tcx> for crate::MiriInterpCx<'mir, 'tcx> {}
  41 pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
  42     /// Returns the minimum alignment for the target architecture for allocations of the given size.
  43     fn min_align(&self, size: u64, kind: MiriMemoryKind) -> Align {
  44         let this = self.eval_context_ref();
  45         // List taken from `library/std/src/sys/common/alloc.rs`.
  46         // This list should be kept in sync with the one from libstd.
  47         let min_align = match this.tcx.sess.target.arch.as_ref() {
  48             "x86" | "arm" | "mips" | "powerpc" | "powerpc64" | "asmjs" | "wasm32" => 8,
  49             "x86_64" | "aarch64" | "mips64" | "s390x" | "sparc64" => 16,
  50             arch => bug!("Unsupported target architecture: {}", arch),
  51         };
  52         // Windows always aligns, even small allocations.
  53         // Source: <https://support.microsoft.com/en-us/help/286470/how-to-use-pageheap-exe-in-windows-xp-windows-2000-and-windows-server>
  54         // But jemalloc does not, so for the C heap we only align if the allocation is sufficiently big.
  55         if kind == MiriMemoryKind::WinHeap || size >= min_align {
  56             return Align::from_bytes(min_align).unwrap();
  57         }
  58         // We have `size < min_align`. Round `size` *down* to the next power of two and use that.
  59         fn prev_power_of_two(x: u64) -> u64 {
  60             let next_pow2 = x.next_power_of_two();
  61             if next_pow2 == x {
  62                 // x *is* a power of two, just use that.
  63                 x
  64             } else {
  65                 // x is between two powers, so next = 2*prev.
  66                 next_pow2 / 2
  67             }
  68         }
  69         Align::from_bytes(prev_power_of_two(size)).unwrap()
  70     }
  71
  72     fn malloc(
  73         &mut self,
  74         size: u64,
  75         zero_init: bool,
  76         kind: MiriMemoryKind,
  77     ) -> InterpResult<'tcx, Pointer<Option<Provenance>>> {
  78         let this = self.eval_context_mut();
  79         if size == 0 {
  80             Ok(Pointer::null())
  81         } else {
  82             let align = this.min_align(size, kind);
  83             let ptr = this.allocate_ptr(Size::from_bytes(size), align, kind.into())?;
  84             if zero_init {
  85                 // We just allocated this, the access is definitely in-bounds and fits into our address space.
  86                 this.write_bytes_ptr(
  87                     ptr.into(),
  88                     iter::repeat(0u8).take(usize::try_from(size).unwrap()),
  89                 )
  90                 .unwrap();
  91             }
  92             Ok(ptr.into())
  93         }
  94     }
  95
  96     fn free(
  97         &mut self,
  98         ptr: Pointer<Option<Provenance>>,
  99         kind: MiriMemoryKind,
 100     ) -> InterpResult<'tcx> {
 101         let this = self.eval_context_mut();
 102         if !this.ptr_is_null(ptr)? {
 103             this.deallocate_ptr(ptr, None, kind.into())?;
 104         }
 105         Ok(())
 106     }
 107
 108     fn realloc(
 109         &mut self,
 110         old_ptr: Pointer<Option<Provenance>>,
 111         new_size: u64,
 112         kind: MiriMemoryKind,
 113     ) -> InterpResult<'tcx, Pointer<Option<Provenance>>> {
 114         let this = self.eval_context_mut();
 115         let new_align = this.min_align(new_size, kind);
 116         if this.ptr_is_null(old_ptr)? {
 117             if new_size == 0 {
 118                 Ok(Pointer::null())
 119             } else {
 120                 let new_ptr =
 121                     this.allocate_ptr(Size::from_bytes(new_size), new_align, kind.into())?;
 122                 Ok(new_ptr.into())
 123             }
 124         } else {
 125             if new_size == 0 {
 126                 this.deallocate_ptr(old_ptr, None, kind.into())?;
 127                 Ok(Pointer::null())
 128             } else {
 129                 let new_ptr = this.reallocate_ptr(
 130                     old_ptr,
 131                     None,
 132                     Size::from_bytes(new_size),
 133                     new_align,
 134                     kind.into(),
 135                 )?;
 136                 Ok(new_ptr.into())
 137             }
 138         }
 139     }
 140
 141     /// Lookup the body of a function that has `link_name` as the symbol name.
 142     fn lookup_exported_symbol(
 143         &mut self,
 144         link_name: Symbol,
 145     ) -> InterpResult<'tcx, Option<(&'mir mir::Body<'tcx>, ty::Instance<'tcx>)>> {
 146         let this = self.eval_context_mut();
 147         let tcx = this.tcx.tcx;
 148
 149         // If the result was cached, just return it.
 150         // (Cannot use `or_insert` since the code below might have to throw an error.)
 151         let entry = this.machine.exported_symbols_cache.entry(link_name);
 152         let instance = *match entry {
 153             Entry::Occupied(e) => e.into_mut(),
 154             Entry::Vacant(e) => {
 155                 // Find it if it was not cached.
 156                 let mut instance_and_crate: Option<(ty::Instance<'_>, CrateNum)> = None;
 157                 // `dependency_formats` includes all the transitive informations needed to link a crate,
 158                 // which is what we need here since we need to dig out `exported_symbols` from all transitive
 159                 // dependencies.
 160                 let dependency_formats = tcx.dependency_formats(());
 161                 let dependency_format = dependency_formats
 162                     .iter()
 163                     .find(|(crate_type, _)| *crate_type == CrateType::Executable)
 164                     .expect("interpreting a non-executable crate");
 165                 for cnum in iter::once(LOCAL_CRATE).chain(
 166                     dependency_format.1.iter().enumerate().filter_map(|(num, &linkage)| {
 167                         // We add 1 to the number because that's what rustc also does everywhere it
 168                         // calls `CrateNum::new`...
 169                         #[allow(clippy::integer_arithmetic)]
 170                         (linkage != Linkage::NotLinked).then_some(CrateNum::new(num + 1))
 171                     }),
 172                 ) {
 173                     // We can ignore `_export_info` here: we are a Rust crate, and everything is exported
 174                     // from a Rust crate.
 175                     for &(symbol, _export_info) in tcx.exported_symbols(cnum) {
 176                         if let ExportedSymbol::NonGeneric(def_id) = symbol {
 177                             let attrs = tcx.codegen_fn_attrs(def_id);
 178                             let symbol_name = if let Some(export_name) = attrs.export_name {
 179                                 export_name
 180                             } else if attrs.flags.contains(CodegenFnAttrFlags::NO_MANGLE) {
 181                                 tcx.item_name(def_id)
 182                             } else {
 183                                 // Skip over items without an explicitly defined symbol name.
 184                                 continue;
 185                             };
 186                             if symbol_name == link_name {
 187                                 if let Some((original_instance, original_cnum)) = instance_and_crate
 188                                 {
 189                                     // Make sure we are consistent wrt what is 'first' and 'second'.
 190                                     let original_span =
 191                                         tcx.def_span(original_instance.def_id()).data();
 192                                     let span = tcx.def_span(def_id).data();
 193                                     if original_span < span {
 194                                         throw_machine_stop!(
 195                                             TerminationInfo::MultipleSymbolDefinitions {
 196                                                 link_name,
 197                                                 first: original_span,
 198                                                 first_crate: tcx.crate_name(original_cnum),
 199                                                 second: span,
 200                                                 second_crate: tcx.crate_name(cnum),
 201                                             }
 202                                         );
 203                                     } else {
 204                                         throw_machine_stop!(
 205                                             TerminationInfo::MultipleSymbolDefinitions {
 206                                                 link_name,
 207                                                 first: span,
 208                                                 first_crate: tcx.crate_name(cnum),
 209                                                 second: original_span,
 210                                                 second_crate: tcx.crate_name(original_cnum),
 211                                             }
 212                                         );
 213                                     }
 214                                 }
 215                                 if !matches!(tcx.def_kind(def_id), DefKind::Fn | DefKind::AssocFn) {
 216                                     throw_ub_format!(
 217                                         "attempt to call an exported symbol that is not defined as a function"
 218                                     );
 219                                 }
 220                                 instance_and_crate = Some((ty::Instance::mono(tcx, def_id), cnum));
 221                             }
 222                         }
 223                     }
 224                 }
 225
 226                 e.insert(instance_and_crate.map(|ic| ic.0))
 227             }
 228         };
 229         match instance {
 230             None => Ok(None), // no symbol with this name
 231             Some(instance) => Ok(Some((this.load_mir(instance.def, None)?, instance))),
 232         }
 233     }
 234
 235     /// Emulates calling a foreign item, failing if the item is not supported.
 236     /// This function will handle `goto_block` if needed.
 237     /// Returns Ok(None) if the foreign item was completely handled
 238     /// by this function.
 239     /// Returns Ok(Some(body)) if processing the foreign item
 240     /// is delegated to another function.
 241     fn emulate_foreign_item(
 242         &mut self,
 243         def_id: DefId,
 244         abi: Abi,
 245         args: &[OpTy<'tcx, Provenance>],
 246         dest: &PlaceTy<'tcx, Provenance>,
 247         ret: Option<mir::BasicBlock>,
 248         unwind: StackPopUnwind,
 249     ) -> InterpResult<'tcx, Option<(&'mir mir::Body<'tcx>, ty::Instance<'tcx>)>> {
 250         let this = self.eval_context_mut();
 251         let link_name = this.item_link_name(def_id);
 252         let tcx = this.tcx.tcx;
 253
 254         // First: functions that diverge.
 255         let ret = match ret {
 256             None =>
 257                 match link_name.as_str() {
 258                     "miri_start_panic" => {
 259                         // `check_shim` happens inside `handle_miri_start_panic`.
 260                         this.handle_miri_start_panic(abi, link_name, args, unwind)?;
 261                         return Ok(None);
 262                     }
 263                     // This matches calls to the foreign item `panic_impl`.
 264                     // The implementation is provided by the function with the `#[panic_handler]` attribute.
 265                     "panic_impl" => {
 266                         // We don't use `check_shim` here because we are just forwarding to the lang
 267                         // item. Argument count checking will be performed when the returned `Body` is
 268                         // called.
 269                         this.check_abi_and_shim_symbol_clash(abi, Abi::Rust, link_name)?;
 270                         let panic_impl_id = tcx.lang_items().panic_impl().unwrap();
 271                         let panic_impl_instance = ty::Instance::mono(tcx, panic_impl_id);
 272                         return Ok(Some((
 273                             this.load_mir(panic_impl_instance.def, None)?,
 274                             panic_impl_instance,
 275                         )));
 276                     }
 277                     #[rustfmt::skip]
 278                     | "exit"
 279                     | "ExitProcess"
 280                     => {
 281                         let exp_abi = if link_name.as_str() == "exit" {
 282                             Abi::C { unwind: false }
 283                         } else {
 284                             Abi::System { unwind: false }
 285                         };
 286                         let [code] = this.check_shim(abi, exp_abi, link_name, args)?;
 287                         // it's really u32 for ExitProcess, but we have to put it into the `Exit` variant anyway
 288                         let code = this.read_scalar(code)?.to_i32()?;
 289                         throw_machine_stop!(TerminationInfo::Exit { code: code.into(), leak_check: false });
 290                     }
 291                     "abort" => {
 292                         let [] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 293                         throw_machine_stop!(TerminationInfo::Abort(
 294                             "the program aborted execution".to_owned()
 295                         ))
 296                     }
 297                     _ => {
 298                         if let Some(body) = this.lookup_exported_symbol(link_name)? {
 299                             return Ok(Some(body));
 300                         }
 301                         this.handle_unsupported(format!(
 302                             "can't call (diverging) foreign function: {link_name}"
 303                         ))?;
 304                         return Ok(None);
 305                     }
 306                 },
 307             Some(p) => p,
 308         };
 309
 310         // Second: functions that return immediately.
 311         match this.emulate_foreign_item_by_name(link_name, abi, args, dest)? {
 312             EmulateByNameResult::NeedsJumping => {
 313                 trace!("{:?}", this.dump_place(**dest));
 314                 this.go_to_block(ret);
 315             }
 316             EmulateByNameResult::AlreadyJumped => (),
 317             EmulateByNameResult::MirBody(mir, instance) => return Ok(Some((mir, instance))),
 318             EmulateByNameResult::NotSupported => {
 319                 if let Some(body) = this.lookup_exported_symbol(link_name)? {
 320                     return Ok(Some(body));
 321                 }
 322
 323                 this.handle_unsupported(format!("can't call foreign function: {link_name}"))?;
 324                 return Ok(None);
 325             }
 326         }
 327
 328         Ok(None)
 329     }
 330
 331     /// Emulates calling the internal __rust_* allocator functions
 332     fn emulate_allocator(
 333         &mut self,
 334         symbol: Symbol,
 335         default: impl FnOnce(&mut MiriInterpCx<'mir, 'tcx>) -> InterpResult<'tcx>,
 336     ) -> InterpResult<'tcx, EmulateByNameResult<'mir, 'tcx>> {
 337         let this = self.eval_context_mut();
 338
 339         let allocator_kind = if let Some(allocator_kind) = this.tcx.allocator_kind(()) {
 340             allocator_kind
 341         } else {
 342             // in real code, this symbol does not exist without an allocator
 343             return Ok(EmulateByNameResult::NotSupported);
 344         };
 345
 346         match allocator_kind {
 347             AllocatorKind::Global => {
 348                 let (body, instance) = this
 349                     .lookup_exported_symbol(symbol)?
 350                     .expect("symbol should be present if there is a global allocator");
 351
 352                 Ok(EmulateByNameResult::MirBody(body, instance))
 353             }
 354             AllocatorKind::Default => {
 355                 default(this)?;
 356                 Ok(EmulateByNameResult::NeedsJumping)
 357             }
 358         }
 359     }
 360
 361     /// Emulates calling a foreign item using its name.
 362     fn emulate_foreign_item_by_name(
 363         &mut self,
 364         link_name: Symbol,
 365         abi: Abi,
 366         args: &[OpTy<'tcx, Provenance>],
 367         dest: &PlaceTy<'tcx, Provenance>,
 368     ) -> InterpResult<'tcx, EmulateByNameResult<'mir, 'tcx>> {
 369         let this = self.eval_context_mut();
 370
 371         // First deal with any external C functions in linked .so file.
 372         #[cfg(target_os = "linux")]
 373         if this.machine.external_so_lib.as_ref().is_some() {
 374             use crate::shims::ffi_support::EvalContextExt as _;
 375             // An Ok(false) here means that the function being called was not exported
 376             // by the specified `.so` file; we should continue and check if it corresponds to
 377             // a provided shim.
 378             if this.call_external_c_fct(link_name, dest, args)? {
 379                 return Ok(EmulateByNameResult::NeedsJumping);
 380             }
 381         }
 382
 383         // When adding a new shim, you should follow the following pattern:
 384         // ```
 385         // "shim_name" => {
 386         //     let [arg1, arg2, arg3] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 387         //     let result = this.shim_name(arg1, arg2, arg3)?;
 388         //     this.write_scalar(result, dest)?;
 389         // }
 390         // ```
 391         // and then define `shim_name` as a helper function in an extension trait in a suitable file
 392         // (see e.g. `unix/fs.rs`):
 393         // ```
 394         // fn shim_name(
 395         //     &mut self,
 396         //     arg1: &OpTy<'tcx, Provenance>,
 397         //     arg2: &OpTy<'tcx, Provenance>,
 398         //     arg3: &OpTy<'tcx, Provenance>)
 399         // -> InterpResult<'tcx, Scalar<Provenance>> {
 400         //     let this = self.eval_context_mut();
 401         //
 402         //     // First thing: load all the arguments. Details depend on the shim.
 403         //     let arg1 = this.read_scalar(arg1)?.to_u32()?;
 404         //     let arg2 = this.read_pointer(arg2)?; // when you need to work with the pointer directly
 405         //     let arg3 = this.deref_operand(arg3)?; // when you want to load/store through the pointer at its declared type
 406         //
 407         //     // ...
 408         //
 409         //     Ok(Scalar::from_u32(42))
 410         // }
 411         // ```
 412         // You might find existing shims not following this pattern, most
 413         // likely because they predate it or because for some reason they cannot be made to fit.
 414
 415         // Here we dispatch all the shims for foreign functions. If you have a platform specific
 416         // shim, add it to the corresponding submodule.
 417         match link_name.as_str() {
 418             // Miri-specific extern functions
 419             "miri_get_alloc_id" => {
 420                 let [ptr] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 421                 let ptr = this.read_pointer(ptr)?;
 422                 let (alloc_id, _, _) = this.ptr_get_alloc_id(ptr).map_err(|_e| {
 423                     err_machine_stop!(TerminationInfo::Abort(
 424                         format!("pointer passed to miri_get_alloc_id must not be dangling, got {ptr:?}")
 425                     ))
 426                 })?;
 427                 this.write_scalar(Scalar::from_u64(alloc_id.0.get()), dest)?;
 428             }
 429             "miri_print_borrow_stacks" => {
 430                 let [id] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 431                 let id = this.read_scalar(id)?.to_u64()?;
 432                 if let Some(id) = std::num::NonZeroU64::new(id) {
 433                     this.print_stacks(AllocId(id))?;
 434                 }
 435             }
 436             "miri_static_root" => {
 437                 let [ptr] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 438                 let ptr = this.read_pointer(ptr)?;
 439                 let (alloc_id, offset, _) = this.ptr_get_alloc_id(ptr)?;
 440                 if offset != Size::ZERO {
 441                     throw_unsup_format!("pointer passed to miri_static_root must point to beginning of an allocated block");
 442                 }
 443                 this.machine.static_roots.push(alloc_id);
 444             }
 445             "miri_host_to_target_path" => {
 446                 let [ptr, out, out_size] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 447                 let ptr = this.read_pointer(ptr)?;
 448                 let out = this.read_pointer(out)?;
 449                 let out_size = this.read_scalar(out_size)?.to_machine_usize(this)?;
 450
 451                 // The host affects program behavior here, so this requires isolation to be disabled.
 452                 this.check_no_isolation("`miri_host_to_target_path`")?;
 453
 454                 // We read this as a plain OsStr and write it as a path, which will convert it to the target.
 455                 let path = this.read_os_str_from_c_str(ptr)?.to_owned();
 456                 let (success, needed_size) = this.write_path_to_c_str(Path::new(&path), out, out_size)?;
 457                 // Return value: 0 on success, otherwise the size it would have needed.
 458                 this.write_int(if success { 0 } else { needed_size }, dest)?;
 459             }
 460
 461             // Obtains the size of a Miri backtrace. See the README for details.
 462             "miri_backtrace_size" => {
 463                 this.handle_miri_backtrace_size(abi, link_name, args, dest)?;
 464             }
 465
 466             // Obtains a Miri backtrace. See the README for details.
 467             "miri_get_backtrace" => {
 468                 // `check_shim` happens inside `handle_miri_get_backtrace`.
 469                 this.handle_miri_get_backtrace(abi, link_name, args, dest)?;
 470             }
 471
 472             // Resolves a Miri backtrace frame. See the README for details.
 473             "miri_resolve_frame" => {
 474                 // `check_shim` happens inside `handle_miri_resolve_frame`.
 475                 this.handle_miri_resolve_frame(abi, link_name, args, dest)?;
 476             }
 477
 478             // Writes the function and file names of a Miri backtrace frame into a user provided buffer. See the README for details.
 479             "miri_resolve_frame_names" => {
 480                 this.handle_miri_resolve_frame_names(abi, link_name, args)?;
 481             }
 482
 483             // Writes some bytes to the interpreter's stdout/stderr. See the
 484             // README for details.
 485             "miri_write_to_stdout" | "miri_write_to_stderr" => {
 486                 let [bytes] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 487                 let (ptr, len) = this.read_immediate(bytes)?.to_scalar_pair();
 488                 let ptr = ptr.to_pointer(this)?;
 489                 let len = len.to_machine_usize(this)?;
 490                 let msg = this.read_bytes_ptr_strip_provenance(ptr, Size::from_bytes(len))?;
 491
 492                 // Note: we're ignoring errors writing to host stdout/stderr.
 493                 let _ignore = match link_name.as_str() {
 494                     "miri_write_to_stdout" => std::io::stdout().write_all(msg),
 495                     "miri_write_to_stderr" => std::io::stderr().write_all(msg),
 496                     _ => unreachable!(),
 497                 };
 498             }
 499
 500             // Standard C allocation
 501             "malloc" => {
 502                 let [size] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 503                 let size = this.read_machine_usize(size)?;
 504                 let res = this.malloc(size, /*zero_init:*/ false, MiriMemoryKind::C)?;
 505                 this.write_pointer(res, dest)?;
 506             }
 507             "calloc" => {
 508                 let [items, len] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 509                 let items = this.read_machine_usize(items)?;
 510                 let len = this.read_machine_usize(len)?;
 511                 let size =
 512                     items.checked_mul(len).ok_or_else(|| err_ub_format!("overflow during calloc size computation"))?;
 513                 let res = this.malloc(size, /*zero_init:*/ true, MiriMemoryKind::C)?;
 514                 this.write_pointer(res, dest)?;
 515             }
 516             "free" => {
 517                 let [ptr] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 518                 let ptr = this.read_pointer(ptr)?;
 519                 this.free(ptr, MiriMemoryKind::C)?;
 520             }
 521             "realloc" => {
 522                 let [old_ptr, new_size] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 523                 let old_ptr = this.read_pointer(old_ptr)?;
 524                 let new_size = this.read_machine_usize(new_size)?;
 525                 let res = this.realloc(old_ptr, new_size, MiriMemoryKind::C)?;
 526                 this.write_pointer(res, dest)?;
 527             }
 528
 529             // Rust allocation
 530             "__rust_alloc" | "miri_alloc" => {
 531                 let [size, align] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 532                 let size = this.read_machine_usize(size)?;
 533                 let align = this.read_machine_usize(align)?;
 534
 535                 let default = |this: &mut MiriInterpCx<'mir, 'tcx>| {
 536                     Self::check_alloc_request(size, align)?;
 537
 538                     let memory_kind = match link_name.as_str() {
 539                         "__rust_alloc" => MiriMemoryKind::Rust,
 540                         "miri_alloc" => MiriMemoryKind::Miri,
 541                         _ => unreachable!(),
 542                     };
 543
 544                     let ptr = this.allocate_ptr(
 545                         Size::from_bytes(size),
 546                         Align::from_bytes(align).unwrap(),
 547                         memory_kind.into(),
 548                     )?;
 549
 550                     this.write_pointer(ptr, dest)
 551                 };
 552
 553                 match link_name.as_str() {
 554                     "__rust_alloc" => return this.emulate_allocator(Symbol::intern("__rg_alloc"), default),
 555                     "miri_alloc" => {
 556                         default(this)?;
 557                         return Ok(EmulateByNameResult::NeedsJumping);
 558                     },
 559                     _ => unreachable!(),
 560                 }
 561             }
 562             "__rust_alloc_zeroed" => {
 563                 let [size, align] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 564                 let size = this.read_machine_usize(size)?;
 565                 let align = this.read_machine_usize(align)?;
 566
 567                 return this.emulate_allocator(Symbol::intern("__rg_alloc_zeroed"), |this| {
 568                     Self::check_alloc_request(size, align)?;
 569
 570                     let ptr = this.allocate_ptr(
 571                         Size::from_bytes(size),
 572                         Align::from_bytes(align).unwrap(),
 573                         MiriMemoryKind::Rust.into(),
 574                     )?;
 575
 576                     // We just allocated this, the access is definitely in-bounds.
 577                     this.write_bytes_ptr(ptr.into(), iter::repeat(0u8).take(usize::try_from(size).unwrap())).unwrap();
 578                     this.write_pointer(ptr, dest)
 579                 });
 580             }
 581             "__rust_dealloc" | "miri_dealloc" => {
 582                 let [ptr, old_size, align] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 583                 let ptr = this.read_pointer(ptr)?;
 584                 let old_size = this.read_machine_usize(old_size)?;
 585                 let align = this.read_machine_usize(align)?;
 586
 587                 let default = |this: &mut MiriInterpCx<'mir, 'tcx>| {
 588                     let memory_kind = match link_name.as_str() {
 589                         "__rust_dealloc" => MiriMemoryKind::Rust,
 590                         "miri_dealloc" => MiriMemoryKind::Miri,
 591                         _ => unreachable!(),
 592                     };
 593
 594                     // No need to check old_size/align; we anyway check that they match the allocation.
 595                     this.deallocate_ptr(
 596                         ptr,
 597                         Some((Size::from_bytes(old_size), Align::from_bytes(align).unwrap())),
 598                         memory_kind.into(),
 599                     )
 600                 };
 601
 602                 match link_name.as_str() {
 603                     "__rust_dealloc" => return this.emulate_allocator(Symbol::intern("__rg_dealloc"), default),
 604                     "miri_dealloc" => {
 605                         default(this)?;
 606                         return Ok(EmulateByNameResult::NeedsJumping);
 607                     }
 608                     _ => unreachable!(),
 609                 }
 610             }
 611             "__rust_realloc" => {
 612                 let [ptr, old_size, align, new_size] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 613                 let ptr = this.read_pointer(ptr)?;
 614                 let old_size = this.read_machine_usize(old_size)?;
 615                 let align = this.read_machine_usize(align)?;
 616                 let new_size = this.read_machine_usize(new_size)?;
 617                 // No need to check old_size; we anyway check that they match the allocation.
 618
 619                 return this.emulate_allocator(Symbol::intern("__rg_realloc"), |this| {
 620                     Self::check_alloc_request(new_size, align)?;
 621
 622                     let align = Align::from_bytes(align).unwrap();
 623                     let new_ptr = this.reallocate_ptr(
 624                         ptr,
 625                         Some((Size::from_bytes(old_size), align)),
 626                         Size::from_bytes(new_size),
 627                         align,
 628                         MiriMemoryKind::Rust.into(),
 629                     )?;
 630                     this.write_pointer(new_ptr, dest)
 631                 });
 632             }
 633
 634             // C memory handling functions
 635             "memcmp" => {
 636                 let [left, right, n] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 637                 let left = this.read_pointer(left)?;
 638                 let right = this.read_pointer(right)?;
 639                 let n = Size::from_bytes(this.read_machine_usize(n)?);
 640
 641                 let result = {
 642                     let left_bytes = this.read_bytes_ptr_strip_provenance(left, n)?;
 643                     let right_bytes = this.read_bytes_ptr_strip_provenance(right, n)?;
 644
 645                     use std::cmp::Ordering::*;
 646                     match left_bytes.cmp(right_bytes) {
 647                         Less => -1i32,
 648                         Equal => 0,
 649                         Greater => 1,
 650                     }
 651                 };
 652
 653                 this.write_scalar(Scalar::from_i32(result), dest)?;
 654             }
 655             "memrchr" => {
 656                 let [ptr, val, num] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 657                 let ptr = this.read_pointer(ptr)?;
 658                 let val = this.read_scalar(val)?.to_i32()?;
 659                 let num = this.read_machine_usize(num)?;
 660                 // The docs say val is "interpreted as unsigned char".
 661                 #[allow(clippy::cast_sign_loss, clippy::cast_possible_truncation)]
 662                 let val = val as u8;
 663
 664                 if let Some(idx) = this
 665                     .read_bytes_ptr_strip_provenance(ptr, Size::from_bytes(num))?
 666                     .iter()
 667                     .rev()
 668                     .position(|&c| c == val)
 669                 {
 670                     let idx = u64::try_from(idx).unwrap();
 671                     #[allow(clippy::integer_arithmetic)] // idx < num, so this never wraps
 672                     let new_ptr = ptr.offset(Size::from_bytes(num - idx - 1), this)?;
 673                     this.write_pointer(new_ptr, dest)?;
 674                 } else {
 675                     this.write_null(dest)?;
 676                 }
 677             }
 678             "memchr" => {
 679                 let [ptr, val, num] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 680                 let ptr = this.read_pointer(ptr)?;
 681                 let val = this.read_scalar(val)?.to_i32()?;
 682                 let num = this.read_machine_usize(num)?;
 683                 // The docs say val is "interpreted as unsigned char".
 684                 #[allow(clippy::cast_sign_loss, clippy::cast_possible_truncation)]
 685                 let val = val as u8;
 686
 687                 let idx = this
 688                     .read_bytes_ptr_strip_provenance(ptr, Size::from_bytes(num))?
 689                     .iter()
 690                     .position(|&c| c == val);
 691                 if let Some(idx) = idx {
 692                     let new_ptr = ptr.offset(Size::from_bytes(idx as u64), this)?;
 693                     this.write_pointer(new_ptr, dest)?;
 694                 } else {
 695                     this.write_null(dest)?;
 696                 }
 697             }
 698             "strlen" => {
 699                 let [ptr] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 700                 let ptr = this.read_pointer(ptr)?;
 701                 let n = this.read_c_str(ptr)?.len();
 702                 this.write_scalar(Scalar::from_machine_usize(u64::try_from(n).unwrap(), this), dest)?;
 703             }
 704
 705             // math functions (note that there are also intrinsics for some other functions)
 706             #[rustfmt::skip]
 707             | "cbrtf"
 708             | "coshf"
 709             | "sinhf"
 710             | "tanf"
 711             | "tanhf"
 712             | "acosf"
 713             | "asinf"
 714             | "atanf"
 715             | "log1pf"
 716             | "expm1f"
 717             => {
 718                 let [f] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 719                 // FIXME: Using host floats.
 720                 let f = f32::from_bits(this.read_scalar(f)?.to_u32()?);
 721                 let res = match link_name.as_str() {
 722                     "cbrtf" => f.cbrt(),
 723                     "coshf" => f.cosh(),
 724                     "sinhf" => f.sinh(),
 725                     "tanf" => f.tan(),
 726                     "tanhf" => f.tanh(),
 727                     "acosf" => f.acos(),
 728                     "asinf" => f.asin(),
 729                     "atanf" => f.atan(),
 730                     "log1pf" => f.ln_1p(),
 731                     "expm1f" => f.exp_m1(),
 732                     _ => bug!(),
 733                 };
 734                 this.write_scalar(Scalar::from_u32(res.to_bits()), dest)?;
 735             }
 736             #[rustfmt::skip]
 737             | "_hypotf"
 738             | "hypotf"
 739             | "atan2f"
 740             | "fdimf"
 741             => {
 742                 let [f1, f2] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 743                 // underscore case for windows, here and below
 744                 // (see https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/floating-point-primitives?view=vs-2019)
 745                 // FIXME: Using host floats.
 746                 let f1 = f32::from_bits(this.read_scalar(f1)?.to_u32()?);
 747                 let f2 = f32::from_bits(this.read_scalar(f2)?.to_u32()?);
 748                 let res = match link_name.as_str() {
 749                     "_hypotf" | "hypotf" => f1.hypot(f2),
 750                     "atan2f" => f1.atan2(f2),
 751                     #[allow(deprecated)]
 752                     "fdimf" => f1.abs_sub(f2),
 753                     _ => bug!(),
 754                 };
 755                 this.write_scalar(Scalar::from_u32(res.to_bits()), dest)?;
 756             }
 757             #[rustfmt::skip]
 758             | "cbrt"
 759             | "cosh"
 760             | "sinh"
 761             | "tan"
 762             | "tanh"
 763             | "acos"
 764             | "asin"
 765             | "atan"
 766             | "log1p"
 767             | "expm1"
 768             => {
 769                 let [f] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 770                 // FIXME: Using host floats.
 771                 let f = f64::from_bits(this.read_scalar(f)?.to_u64()?);
 772                 let res = match link_name.as_str() {
 773                     "cbrt" => f.cbrt(),
 774                     "cosh" => f.cosh(),
 775                     "sinh" => f.sinh(),
 776                     "tan" => f.tan(),
 777                     "tanh" => f.tanh(),
 778                     "acos" => f.acos(),
 779                     "asin" => f.asin(),
 780                     "atan" => f.atan(),
 781                     "log1p" => f.ln_1p(),
 782                     "expm1" => f.exp_m1(),
 783                     _ => bug!(),
 784                 };
 785                 this.write_scalar(Scalar::from_u64(res.to_bits()), dest)?;
 786             }
 787             #[rustfmt::skip]
 788             | "_hypot"
 789             | "hypot"
 790             | "atan2"
 791             | "fdim"
 792             => {
 793                 let [f1, f2] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 794                 // FIXME: Using host floats.
 795                 let f1 = f64::from_bits(this.read_scalar(f1)?.to_u64()?);
 796                 let f2 = f64::from_bits(this.read_scalar(f2)?.to_u64()?);
 797                 let res = match link_name.as_str() {
 798                     "_hypot" | "hypot" => f1.hypot(f2),
 799                     "atan2" => f1.atan2(f2),
 800                     #[allow(deprecated)]
 801                     "fdim" => f1.abs_sub(f2),
 802                     _ => bug!(),
 803                 };
 804                 this.write_scalar(Scalar::from_u64(res.to_bits()), dest)?;
 805             }
 806             #[rustfmt::skip]
 807             | "_ldexp"
 808             | "ldexp"
 809             | "scalbn"
 810             => {
 811                 let [x, exp] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 812                 // For radix-2 (binary) systems, `ldexp` and `scalbn` are the same.
 813                 let x = this.read_scalar(x)?.to_f64()?;
 814                 let exp = this.read_scalar(exp)?.to_i32()?;
 815
 816                 // Saturating cast to i16. Even those are outside the valid exponent range so
 817                 // `scalbn` below will do its over/underflow handling.
 818                 let exp = if exp > i32::from(i16::MAX) {
 819                     i16::MAX
 820                 } else if exp < i32::from(i16::MIN) {
 821                     i16::MIN
 822                 } else {
 823                     exp.try_into().unwrap()
 824                 };
 825
 826                 let res = x.scalbn(exp);
 827                 this.write_scalar(Scalar::from_f64(res), dest)?;
 828             }
 829
 830             // Architecture-specific shims
 831             "llvm.x86.addcarry.64" if this.tcx.sess.target.arch == "x86_64" => {
 832                 // Computes u8+u64+u64, returning tuple (u8,u64) comprising the output carry and truncated sum.
 833                 let [c_in, a, b] = this.check_shim(abi, Abi::Unadjusted, link_name, args)?;
 834                 let c_in = this.read_scalar(c_in)?.to_u8()?;
 835                 let a = this.read_scalar(a)?.to_u64()?;
 836                 let b = this.read_scalar(b)?.to_u64()?;
 837
 838                 #[allow(clippy::integer_arithmetic)] // adding two u64 and a u8 cannot wrap in a u128
 839                 let wide_sum = u128::from(c_in) + u128::from(a) + u128::from(b);
 840                 #[allow(clippy::integer_arithmetic)] // it's a u128, we can shift by 64
 841                 let (c_out, sum) = ((wide_sum >> 64).truncate::<u8>(), wide_sum.truncate::<u64>());
 842
 843                 let c_out_field = this.place_field(dest, 0)?;
 844                 this.write_scalar(Scalar::from_u8(c_out), &c_out_field)?;
 845                 let sum_field = this.place_field(dest, 1)?;
 846                 this.write_scalar(Scalar::from_u64(sum), &sum_field)?;
 847             }
 848             "llvm.x86.sse2.pause" if this.tcx.sess.target.arch == "x86" || this.tcx.sess.target.arch == "x86_64" => {
 849                 let [] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 850                 this.yield_active_thread();
 851             }
 852             "llvm.aarch64.isb" if this.tcx.sess.target.arch == "aarch64" => {
 853                 let [arg] = this.check_shim(abi, Abi::Unadjusted, link_name, args)?;
 854                 let arg = this.read_scalar(arg)?.to_i32()?;
 855                 match arg {
 856                     15 => { // SY ("full system scope")
 857                         this.yield_active_thread();
 858                     }
 859                     _ => {
 860                         throw_unsup_format!("unsupported llvm.aarch64.isb argument {}", arg);
 861                     }
 862                 }
 863             }
 864
 865             // Platform-specific shims
 866             _ => match this.tcx.sess.target.os.as_ref() {
 867                 target if target_os_is_unix(target) => return shims::unix::foreign_items::EvalContextExt::emulate_foreign_item_by_name(this, link_name, abi, args, dest),
 868                 "windows" => return shims::windows::foreign_items::EvalContextExt::emulate_foreign_item_by_name(this, link_name, abi, args, dest),
 869                 target => throw_unsup_format!("the target `{}` is not supported", target),
 870             }
 871         };
 872         // We only fall through to here if we did *not* hit the `_` arm above,
 873         // i.e., if we actually emulated the function with one of the shims.
 874         Ok(EmulateByNameResult::NeedsJumping)
 875     }
 876
 877     /// Check some basic requirements for this allocation request:
 878     /// non-zero size, power-of-two alignment.
 879     fn check_alloc_request(size: u64, align: u64) -> InterpResult<'tcx> {
 880         if size == 0 {
 881             throw_ub_format!("creating allocation with size 0");
 882         }
 883         if !align.is_power_of_two() {
 884             throw_ub_format!("creating allocation with non-power-of-two alignment {}", align);
 885         }
 886         Ok(())
 887     }
 888 }