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 for malloc: `{}`", 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!(
 324                     "can't call foreign function `{link_name}` on OS `{os}`",
 325                     os = this.tcx.sess.target.os,
 326                 ))?;
 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 Some(allocator_kind) = this.tcx.allocator_kind(()) else {
 343             // in real code, this symbol does not exist without an allocator
 344             return Ok(EmulateByNameResult::NotSupported);
 345         };
 346
 347         match allocator_kind {
 348             AllocatorKind::Global => {
 349                 let (body, instance) = this
 350                     .lookup_exported_symbol(symbol)?
 351                     .expect("symbol should be present if there is a global allocator");
 352
 353                 Ok(EmulateByNameResult::MirBody(body, instance))
 354             }
 355             AllocatorKind::Default => {
 356                 default(this)?;
 357                 Ok(EmulateByNameResult::NeedsJumping)
 358             }
 359         }
 360     }
 361
 362     /// Emulates calling a foreign item using its name.
 363     fn emulate_foreign_item_by_name(
 364         &mut self,
 365         link_name: Symbol,
 366         abi: Abi,
 367         args: &[OpTy<'tcx, Provenance>],
 368         dest: &PlaceTy<'tcx, Provenance>,
 369     ) -> InterpResult<'tcx, EmulateByNameResult<'mir, 'tcx>> {
 370         let this = self.eval_context_mut();
 371
 372         // First deal with any external C functions in linked .so file.
 373         #[cfg(target_os = "linux")]
 374         if this.machine.external_so_lib.as_ref().is_some() {
 375             use crate::shims::ffi_support::EvalContextExt as _;
 376             // An Ok(false) here means that the function being called was not exported
 377             // by the specified `.so` file; we should continue and check if it corresponds to
 378             // a provided shim.
 379             if this.call_external_c_fct(link_name, dest, args)? {
 380                 return Ok(EmulateByNameResult::NeedsJumping);
 381             }
 382         }
 383
 384         // When adding a new shim, you should follow the following pattern:
 385         // ```
 386         // "shim_name" => {
 387         //     let [arg1, arg2, arg3] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 388         //     let result = this.shim_name(arg1, arg2, arg3)?;
 389         //     this.write_scalar(result, dest)?;
 390         // }
 391         // ```
 392         // and then define `shim_name` as a helper function in an extension trait in a suitable file
 393         // (see e.g. `unix/fs.rs`):
 394         // ```
 395         // fn shim_name(
 396         //     &mut self,
 397         //     arg1: &OpTy<'tcx, Provenance>,
 398         //     arg2: &OpTy<'tcx, Provenance>,
 399         //     arg3: &OpTy<'tcx, Provenance>)
 400         // -> InterpResult<'tcx, Scalar<Provenance>> {
 401         //     let this = self.eval_context_mut();
 402         //
 403         //     // First thing: load all the arguments. Details depend on the shim.
 404         //     let arg1 = this.read_scalar(arg1)?.to_u32()?;
 405         //     let arg2 = this.read_pointer(arg2)?; // when you need to work with the pointer directly
 406         //     let arg3 = this.deref_operand(arg3)?; // when you want to load/store through the pointer at its declared type
 407         //
 408         //     // ...
 409         //
 410         //     Ok(Scalar::from_u32(42))
 411         // }
 412         // ```
 413         // You might find existing shims not following this pattern, most
 414         // likely because they predate it or because for some reason they cannot be made to fit.
 415
 416         // Here we dispatch all the shims for foreign functions. If you have a platform specific
 417         // shim, add it to the corresponding submodule.
 418         match link_name.as_str() {
 419             // Miri-specific extern functions
 420             "miri_get_alloc_id" => {
 421                 let [ptr] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 422                 let ptr = this.read_pointer(ptr)?;
 423                 let (alloc_id, _, _) = this.ptr_get_alloc_id(ptr).map_err(|_e| {
 424                     err_machine_stop!(TerminationInfo::Abort(format!(
 425                         "pointer passed to miri_get_alloc_id must not be dangling, got {ptr:?}"
 426                     )))
 427                 })?;
 428                 this.write_scalar(Scalar::from_u64(alloc_id.0.get()), dest)?;
 429             }
 430             "miri_print_borrow_stacks" => {
 431                 let [id] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 432                 let id = this.read_scalar(id)?.to_u64()?;
 433                 if let Some(id) = std::num::NonZeroU64::new(id) {
 434                     this.print_stacks(AllocId(id))?;
 435                 }
 436             }
 437             "miri_static_root" => {
 438                 let [ptr] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 439                 let ptr = this.read_pointer(ptr)?;
 440                 let (alloc_id, offset, _) = this.ptr_get_alloc_id(ptr)?;
 441                 if offset != Size::ZERO {
 442                     throw_unsup_format!(
 443                         "pointer passed to miri_static_root must point to beginning of an allocated block"
 444                     );
 445                 }
 446                 this.machine.static_roots.push(alloc_id);
 447             }
 448             "miri_host_to_target_path" => {
 449                 let [ptr, out, out_size] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 450                 let ptr = this.read_pointer(ptr)?;
 451                 let out = this.read_pointer(out)?;
 452                 let out_size = this.read_scalar(out_size)?.to_machine_usize(this)?;
 453
 454                 // The host affects program behavior here, so this requires isolation to be disabled.
 455                 this.check_no_isolation("`miri_host_to_target_path`")?;
 456
 457                 // We read this as a plain OsStr and write it as a path, which will convert it to the target.
 458                 let path = this.read_os_str_from_c_str(ptr)?.to_owned();
 459                 let (success, needed_size) =
 460                     this.write_path_to_c_str(Path::new(&path), out, out_size)?;
 461                 // Return value: 0 on success, otherwise the size it would have needed.
 462                 this.write_int(if success { 0 } else { needed_size }, dest)?;
 463             }
 464
 465             // Obtains the size of a Miri backtrace. See the README for details.
 466             "miri_backtrace_size" => {
 467                 this.handle_miri_backtrace_size(abi, link_name, args, dest)?;
 468             }
 469
 470             // Obtains a Miri backtrace. See the README for details.
 471             "miri_get_backtrace" => {
 472                 // `check_shim` happens inside `handle_miri_get_backtrace`.
 473                 this.handle_miri_get_backtrace(abi, link_name, args, dest)?;
 474             }
 475
 476             // Resolves a Miri backtrace frame. See the README for details.
 477             "miri_resolve_frame" => {
 478                 // `check_shim` happens inside `handle_miri_resolve_frame`.
 479                 this.handle_miri_resolve_frame(abi, link_name, args, dest)?;
 480             }
 481
 482             // Writes the function and file names of a Miri backtrace frame into a user provided buffer. See the README for details.
 483             "miri_resolve_frame_names" => {
 484                 this.handle_miri_resolve_frame_names(abi, link_name, args)?;
 485             }
 486
 487             // Writes some bytes to the interpreter's stdout/stderr. See the
 488             // README for details.
 489             "miri_write_to_stdout" | "miri_write_to_stderr" => {
 490                 let [bytes] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 491                 let (ptr, len) = this.read_immediate(bytes)?.to_scalar_pair();
 492                 let ptr = ptr.to_pointer(this)?;
 493                 let len = len.to_machine_usize(this)?;
 494                 let msg = this.read_bytes_ptr_strip_provenance(ptr, Size::from_bytes(len))?;
 495
 496                 // Note: we're ignoring errors writing to host stdout/stderr.
 497                 let _ignore = match link_name.as_str() {
 498                     "miri_write_to_stdout" => std::io::stdout().write_all(msg),
 499                     "miri_write_to_stderr" => std::io::stderr().write_all(msg),
 500                     _ => unreachable!(),
 501                 };
 502             }
 503
 504             // Standard C allocation
 505             "malloc" => {
 506                 let [size] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 507                 let size = this.read_machine_usize(size)?;
 508                 let res = this.malloc(size, /*zero_init:*/ false, MiriMemoryKind::C)?;
 509                 this.write_pointer(res, dest)?;
 510             }
 511             "calloc" => {
 512                 let [items, len] =
 513                     this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 514                 let items = this.read_machine_usize(items)?;
 515                 let len = this.read_machine_usize(len)?;
 516                 let size = items
 517                     .checked_mul(len)
 518                     .ok_or_else(|| err_ub_format!("overflow during calloc size computation"))?;
 519                 let res = this.malloc(size, /*zero_init:*/ true, MiriMemoryKind::C)?;
 520                 this.write_pointer(res, dest)?;
 521             }
 522             "free" => {
 523                 let [ptr] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 524                 let ptr = this.read_pointer(ptr)?;
 525                 this.free(ptr, MiriMemoryKind::C)?;
 526             }
 527             "realloc" => {
 528                 let [old_ptr, new_size] =
 529                     this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 530                 let old_ptr = this.read_pointer(old_ptr)?;
 531                 let new_size = this.read_machine_usize(new_size)?;
 532                 let res = this.realloc(old_ptr, new_size, MiriMemoryKind::C)?;
 533                 this.write_pointer(res, dest)?;
 534             }
 535
 536             // Rust allocation
 537             "__rust_alloc" | "miri_alloc" => {
 538                 let [size, align] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 539                 let size = this.read_machine_usize(size)?;
 540                 let align = this.read_machine_usize(align)?;
 541
 542                 let default = |this: &mut MiriInterpCx<'mir, 'tcx>| {
 543                     Self::check_alloc_request(size, align)?;
 544
 545                     let memory_kind = match link_name.as_str() {
 546                         "__rust_alloc" => MiriMemoryKind::Rust,
 547                         "miri_alloc" => MiriMemoryKind::Miri,
 548                         _ => unreachable!(),
 549                     };
 550
 551                     let ptr = this.allocate_ptr(
 552                         Size::from_bytes(size),
 553                         Align::from_bytes(align).unwrap(),
 554                         memory_kind.into(),
 555                     )?;
 556
 557                     this.write_pointer(ptr, dest)
 558                 };
 559
 560                 match link_name.as_str() {
 561                     "__rust_alloc" =>
 562                         return this.emulate_allocator(Symbol::intern("__rg_alloc"), default),
 563                     "miri_alloc" => {
 564                         default(this)?;
 565                         return Ok(EmulateByNameResult::NeedsJumping);
 566                     }
 567                     _ => unreachable!(),
 568                 }
 569             }
 570             "__rust_alloc_zeroed" => {
 571                 let [size, align] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 572                 let size = this.read_machine_usize(size)?;
 573                 let align = this.read_machine_usize(align)?;
 574
 575                 return this.emulate_allocator(Symbol::intern("__rg_alloc_zeroed"), |this| {
 576                     Self::check_alloc_request(size, align)?;
 577
 578                     let ptr = this.allocate_ptr(
 579                         Size::from_bytes(size),
 580                         Align::from_bytes(align).unwrap(),
 581                         MiriMemoryKind::Rust.into(),
 582                     )?;
 583
 584                     // We just allocated this, the access is definitely in-bounds.
 585                     this.write_bytes_ptr(
 586                         ptr.into(),
 587                         iter::repeat(0u8).take(usize::try_from(size).unwrap()),
 588                     )
 589                     .unwrap();
 590                     this.write_pointer(ptr, dest)
 591                 });
 592             }
 593             "__rust_dealloc" | "miri_dealloc" => {
 594                 let [ptr, old_size, align] = this.check_shim(abi, Abi::Rust, link_name, args)?;
 595                 let ptr = this.read_pointer(ptr)?;
 596                 let old_size = this.read_machine_usize(old_size)?;
 597                 let align = this.read_machine_usize(align)?;
 598
 599                 let default = |this: &mut MiriInterpCx<'mir, 'tcx>| {
 600                     let memory_kind = match link_name.as_str() {
 601                         "__rust_dealloc" => MiriMemoryKind::Rust,
 602                         "miri_dealloc" => MiriMemoryKind::Miri,
 603                         _ => unreachable!(),
 604                     };
 605
 606                     // No need to check old_size/align; we anyway check that they match the allocation.
 607                     this.deallocate_ptr(
 608                         ptr,
 609                         Some((Size::from_bytes(old_size), Align::from_bytes(align).unwrap())),
 610                         memory_kind.into(),
 611                     )
 612                 };
 613
 614                 match link_name.as_str() {
 615                     "__rust_dealloc" =>
 616                         return this.emulate_allocator(Symbol::intern("__rg_dealloc"), default),
 617                     "miri_dealloc" => {
 618                         default(this)?;
 619                         return Ok(EmulateByNameResult::NeedsJumping);
 620                     }
 621                     _ => unreachable!(),
 622                 }
 623             }
 624             "__rust_realloc" => {
 625                 let [ptr, old_size, align, new_size] =
 626                     this.check_shim(abi, Abi::Rust, link_name, args)?;
 627                 let ptr = this.read_pointer(ptr)?;
 628                 let old_size = this.read_machine_usize(old_size)?;
 629                 let align = this.read_machine_usize(align)?;
 630                 let new_size = this.read_machine_usize(new_size)?;
 631                 // No need to check old_size; we anyway check that they match the allocation.
 632
 633                 return this.emulate_allocator(Symbol::intern("__rg_realloc"), |this| {
 634                     Self::check_alloc_request(new_size, align)?;
 635
 636                     let align = Align::from_bytes(align).unwrap();
 637                     let new_ptr = this.reallocate_ptr(
 638                         ptr,
 639                         Some((Size::from_bytes(old_size), align)),
 640                         Size::from_bytes(new_size),
 641                         align,
 642                         MiriMemoryKind::Rust.into(),
 643                     )?;
 644                     this.write_pointer(new_ptr, dest)
 645                 });
 646             }
 647
 648             // C memory handling functions
 649             "memcmp" => {
 650                 let [left, right, n] =
 651                     this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 652                 let left = this.read_pointer(left)?;
 653                 let right = this.read_pointer(right)?;
 654                 let n = Size::from_bytes(this.read_machine_usize(n)?);
 655
 656                 let result = {
 657                     let left_bytes = this.read_bytes_ptr_strip_provenance(left, n)?;
 658                     let right_bytes = this.read_bytes_ptr_strip_provenance(right, n)?;
 659
 660                     use std::cmp::Ordering::*;
 661                     match left_bytes.cmp(right_bytes) {
 662                         Less => -1i32,
 663                         Equal => 0,
 664                         Greater => 1,
 665                     }
 666                 };
 667
 668                 this.write_scalar(Scalar::from_i32(result), dest)?;
 669             }
 670             "memrchr" => {
 671                 let [ptr, val, num] =
 672                     this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 673                 let ptr = this.read_pointer(ptr)?;
 674                 let val = this.read_scalar(val)?.to_i32()?;
 675                 let num = this.read_machine_usize(num)?;
 676                 // The docs say val is "interpreted as unsigned char".
 677                 #[allow(clippy::cast_sign_loss, clippy::cast_possible_truncation)]
 678                 let val = val as u8;
 679
 680                 if let Some(idx) = this
 681                     .read_bytes_ptr_strip_provenance(ptr, Size::from_bytes(num))?
 682                     .iter()
 683                     .rev()
 684                     .position(|&c| c == val)
 685                 {
 686                     let idx = u64::try_from(idx).unwrap();
 687                     #[allow(clippy::integer_arithmetic)] // idx < num, so this never wraps
 688                     let new_ptr = ptr.offset(Size::from_bytes(num - idx - 1), this)?;
 689                     this.write_pointer(new_ptr, dest)?;
 690                 } else {
 691                     this.write_null(dest)?;
 692                 }
 693             }
 694             "memchr" => {
 695                 let [ptr, val, num] =
 696                     this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 697                 let ptr = this.read_pointer(ptr)?;
 698                 let val = this.read_scalar(val)?.to_i32()?;
 699                 let num = this.read_machine_usize(num)?;
 700                 // The docs say val is "interpreted as unsigned char".
 701                 #[allow(clippy::cast_sign_loss, clippy::cast_possible_truncation)]
 702                 let val = val as u8;
 703
 704                 let idx = this
 705                     .read_bytes_ptr_strip_provenance(ptr, Size::from_bytes(num))?
 706                     .iter()
 707                     .position(|&c| c == val);
 708                 if let Some(idx) = idx {
 709                     let new_ptr = ptr.offset(Size::from_bytes(idx as u64), this)?;
 710                     this.write_pointer(new_ptr, dest)?;
 711                 } else {
 712                     this.write_null(dest)?;
 713                 }
 714             }
 715             "strlen" => {
 716                 let [ptr] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 717                 let ptr = this.read_pointer(ptr)?;
 718                 let n = this.read_c_str(ptr)?.len();
 719                 this.write_scalar(
 720                     Scalar::from_machine_usize(u64::try_from(n).unwrap(), this),
 721                     dest,
 722                 )?;
 723             }
 724
 725             // math functions (note that there are also intrinsics for some other functions)
 726             #[rustfmt::skip]
 727             | "cbrtf"
 728             | "coshf"
 729             | "sinhf"
 730             | "tanf"
 731             | "tanhf"
 732             | "acosf"
 733             | "asinf"
 734             | "atanf"
 735             | "log1pf"
 736             | "expm1f"
 737             => {
 738                 let [f] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 739                 // FIXME: Using host floats.
 740                 let f = f32::from_bits(this.read_scalar(f)?.to_u32()?);
 741                 let res = match link_name.as_str() {
 742                     "cbrtf" => f.cbrt(),
 743                     "coshf" => f.cosh(),
 744                     "sinhf" => f.sinh(),
 745                     "tanf" => f.tan(),
 746                     "tanhf" => f.tanh(),
 747                     "acosf" => f.acos(),
 748                     "asinf" => f.asin(),
 749                     "atanf" => f.atan(),
 750                     "log1pf" => f.ln_1p(),
 751                     "expm1f" => f.exp_m1(),
 752                     _ => bug!(),
 753                 };
 754                 this.write_scalar(Scalar::from_u32(res.to_bits()), dest)?;
 755             }
 756             #[rustfmt::skip]
 757             | "_hypotf"
 758             | "hypotf"
 759             | "atan2f"
 760             | "fdimf"
 761             => {
 762                 let [f1, f2] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 763                 // underscore case for windows, here and below
 764                 // (see https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/floating-point-primitives?view=vs-2019)
 765                 // FIXME: Using host floats.
 766                 let f1 = f32::from_bits(this.read_scalar(f1)?.to_u32()?);
 767                 let f2 = f32::from_bits(this.read_scalar(f2)?.to_u32()?);
 768                 let res = match link_name.as_str() {
 769                     "_hypotf" | "hypotf" => f1.hypot(f2),
 770                     "atan2f" => f1.atan2(f2),
 771                     #[allow(deprecated)]
 772                     "fdimf" => f1.abs_sub(f2),
 773                     _ => bug!(),
 774                 };
 775                 this.write_scalar(Scalar::from_u32(res.to_bits()), dest)?;
 776             }
 777             #[rustfmt::skip]
 778             | "cbrt"
 779             | "cosh"
 780             | "sinh"
 781             | "tan"
 782             | "tanh"
 783             | "acos"
 784             | "asin"
 785             | "atan"
 786             | "log1p"
 787             | "expm1"
 788             => {
 789                 let [f] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 790                 // FIXME: Using host floats.
 791                 let f = f64::from_bits(this.read_scalar(f)?.to_u64()?);
 792                 let res = match link_name.as_str() {
 793                     "cbrt" => f.cbrt(),
 794                     "cosh" => f.cosh(),
 795                     "sinh" => f.sinh(),
 796                     "tan" => f.tan(),
 797                     "tanh" => f.tanh(),
 798                     "acos" => f.acos(),
 799                     "asin" => f.asin(),
 800                     "atan" => f.atan(),
 801                     "log1p" => f.ln_1p(),
 802                     "expm1" => f.exp_m1(),
 803                     _ => bug!(),
 804                 };
 805                 this.write_scalar(Scalar::from_u64(res.to_bits()), dest)?;
 806             }
 807             #[rustfmt::skip]
 808             | "_hypot"
 809             | "hypot"
 810             | "atan2"
 811             | "fdim"
 812             => {
 813                 let [f1, f2] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 814                 // FIXME: Using host floats.
 815                 let f1 = f64::from_bits(this.read_scalar(f1)?.to_u64()?);
 816                 let f2 = f64::from_bits(this.read_scalar(f2)?.to_u64()?);
 817                 let res = match link_name.as_str() {
 818                     "_hypot" | "hypot" => f1.hypot(f2),
 819                     "atan2" => f1.atan2(f2),
 820                     #[allow(deprecated)]
 821                     "fdim" => f1.abs_sub(f2),
 822                     _ => bug!(),
 823                 };
 824                 this.write_scalar(Scalar::from_u64(res.to_bits()), dest)?;
 825             }
 826             #[rustfmt::skip]
 827             | "_ldexp"
 828             | "ldexp"
 829             | "scalbn"
 830             => {
 831                 let [x, exp] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 832                 // For radix-2 (binary) systems, `ldexp` and `scalbn` are the same.
 833                 let x = this.read_scalar(x)?.to_f64()?;
 834                 let exp = this.read_scalar(exp)?.to_i32()?;
 835
 836                 // Saturating cast to i16. Even those are outside the valid exponent range so
 837                 // `scalbn` below will do its over/underflow handling.
 838                 let exp = if exp > i32::from(i16::MAX) {
 839                     i16::MAX
 840                 } else if exp < i32::from(i16::MIN) {
 841                     i16::MIN
 842                 } else {
 843                     exp.try_into().unwrap()
 844                 };
 845
 846                 let res = x.scalbn(exp);
 847                 this.write_scalar(Scalar::from_f64(res), dest)?;
 848             }
 849
 850             // Architecture-specific shims
 851             "llvm.x86.addcarry.64" if this.tcx.sess.target.arch == "x86_64" => {
 852                 // Computes u8+u64+u64, returning tuple (u8,u64) comprising the output carry and truncated sum.
 853                 let [c_in, a, b] = this.check_shim(abi, Abi::Unadjusted, link_name, args)?;
 854                 let c_in = this.read_scalar(c_in)?.to_u8()?;
 855                 let a = this.read_scalar(a)?.to_u64()?;
 856                 let b = this.read_scalar(b)?.to_u64()?;
 857
 858                 #[allow(clippy::integer_arithmetic)]
 859                 // adding two u64 and a u8 cannot wrap in a u128
 860                 let wide_sum = u128::from(c_in) + u128::from(a) + u128::from(b);
 861                 #[allow(clippy::integer_arithmetic)] // it's a u128, we can shift by 64
 862                 let (c_out, sum) = ((wide_sum >> 64).truncate::<u8>(), wide_sum.truncate::<u64>());
 863
 864                 let c_out_field = this.place_field(dest, 0)?;
 865                 this.write_scalar(Scalar::from_u8(c_out), &c_out_field)?;
 866                 let sum_field = this.place_field(dest, 1)?;
 867                 this.write_scalar(Scalar::from_u64(sum), &sum_field)?;
 868             }
 869             "llvm.x86.sse2.pause"
 870                 if this.tcx.sess.target.arch == "x86" || this.tcx.sess.target.arch == "x86_64" =>
 871             {
 872                 let [] = this.check_shim(abi, Abi::C { unwind: false }, link_name, args)?;
 873                 this.yield_active_thread();
 874             }
 875             "llvm.aarch64.isb" if this.tcx.sess.target.arch == "aarch64" => {
 876                 let [arg] = this.check_shim(abi, Abi::Unadjusted, link_name, args)?;
 877                 let arg = this.read_scalar(arg)?.to_i32()?;
 878                 match arg {
 879                     // SY ("full system scope")
 880                     15 => {
 881                         this.yield_active_thread();
 882                     }
 883                     _ => {
 884                         throw_unsup_format!("unsupported llvm.aarch64.isb argument {}", arg);
 885                     }
 886                 }
 887             }
 888
 889             // Platform-specific shims
 890             _ =>
 891                 return match this.tcx.sess.target.os.as_ref() {
 892                     target_os if target_os_is_unix(target_os) =>
 893                         shims::unix::foreign_items::EvalContextExt::emulate_foreign_item_by_name(
 894                             this, link_name, abi, args, dest,
 895                         ),
 896                     "windows" =>
 897                         shims::windows::foreign_items::EvalContextExt::emulate_foreign_item_by_name(
 898                             this, link_name, abi, args, dest,
 899                         ),
 900                     _ => Ok(EmulateByNameResult::NotSupported),
 901                 },
 902         };
 903         // We only fall through to here if we did *not* hit the `_` arm above,
 904         // i.e., if we actually emulated the function with one of the shims.
 905         Ok(EmulateByNameResult::NeedsJumping)
 906     }
 907
 908     /// Check some basic requirements for this allocation request:
 909     /// non-zero size, power-of-two alignment.
 910     fn check_alloc_request(size: u64, align: u64) -> InterpResult<'tcx> {
 911         if size == 0 {
 912             throw_ub_format!("creating allocation with size 0");
 913         }
 914         if !align.is_power_of_two() {
 915             throw_ub_format!("creating allocation with non-power-of-two alignment {}", align);
 916         }
 917         Ok(())
 918     }
 919 }