src/shims/foreign_items.rs

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