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