src/shims/foreign_items.rs

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