rustc_middle/mir/interpret/mod.rs
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//! An interpreter for MIR used in CTFE and by miri.
#[macro_use]
mod error;
mod allocation;
mod pointer;
mod queries;
mod value;
use std::io::{Read, Write};
use std::num::NonZero;
use std::{fmt, io};
use rustc_ast::LitKind;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::sync::Lock;
use rustc_errors::ErrorGuaranteed;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisitable};
use rustc_middle::ty::print::with_no_trimmed_paths;
use rustc_serialize::{Decodable, Encodable};
use rustc_target::abi::{AddressSpace, Endian, HasDataLayout};
use tracing::{debug, trace};
// Also make the error macros available from this module.
pub use {
err_exhaust, err_inval, err_machine_stop, err_ub, err_ub_custom, err_ub_format, err_unsup,
err_unsup_format, throw_exhaust, throw_inval, throw_machine_stop, throw_ub, throw_ub_custom,
throw_ub_format, throw_unsup, throw_unsup_format,
};
pub use self::allocation::{
AllocBytes, AllocError, AllocRange, AllocResult, Allocation, ConstAllocation, InitChunk,
InitChunkIter, alloc_range,
};
pub use self::error::{
BadBytesAccess, CheckAlignMsg, CheckInAllocMsg, ErrorHandled, EvalStaticInitializerRawResult,
EvalToAllocationRawResult, EvalToConstValueResult, EvalToValTreeResult, ExpectedKind,
InterpError, InterpErrorInfo, InterpResult, InvalidMetaKind, InvalidProgramInfo,
MachineStopType, Misalignment, PointerKind, ReportedErrorInfo, ResourceExhaustionInfo,
ScalarSizeMismatch, UndefinedBehaviorInfo, UnsupportedOpInfo, ValidationErrorInfo,
ValidationErrorKind, interp_ok,
};
pub use self::pointer::{CtfeProvenance, Pointer, PointerArithmetic, Provenance};
pub use self::value::Scalar;
use crate::mir;
use crate::ty::codec::{TyDecoder, TyEncoder};
use crate::ty::{self, Instance, Ty, TyCtxt};
/// Uniquely identifies one of the following:
/// - A constant
/// - A static
#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, TyEncodable, TyDecodable)]
#[derive(HashStable, TypeFoldable, TypeVisitable)]
pub struct GlobalId<'tcx> {
/// For a constant or static, the `Instance` of the item itself.
/// For a promoted global, the `Instance` of the function they belong to.
pub instance: ty::Instance<'tcx>,
/// The index for promoted globals within their function's `mir::Body`.
pub promoted: Option<mir::Promoted>,
}
impl<'tcx> GlobalId<'tcx> {
pub fn display(self, tcx: TyCtxt<'tcx>) -> String {
let instance_name = with_no_trimmed_paths!(tcx.def_path_str(self.instance.def.def_id()));
if let Some(promoted) = self.promoted {
format!("{instance_name}::{promoted:?}")
} else {
instance_name
}
}
}
/// Input argument for `tcx.lit_to_const`.
#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash, HashStable)]
pub struct LitToConstInput<'tcx> {
/// The absolute value of the resultant constant.
pub lit: &'tcx LitKind,
/// The type of the constant.
pub ty: Ty<'tcx>,
/// If the constant is negative.
pub neg: bool,
}
/// Error type for `tcx.lit_to_const`.
#[derive(Copy, Clone, Debug, Eq, PartialEq, HashStable)]
pub enum LitToConstError {
/// The literal's inferred type did not match the expected `ty` in the input.
/// This is used for graceful error handling (`span_delayed_bug`) in
/// type checking (`Const::from_anon_const`).
TypeError,
Reported(ErrorGuaranteed),
}
#[derive(Copy, Clone, Eq, Hash, Ord, PartialEq, PartialOrd)]
pub struct AllocId(pub NonZero<u64>);
// We want the `Debug` output to be readable as it is used by `derive(Debug)` for
// all the Miri types.
impl fmt::Debug for AllocId {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
if f.alternate() { write!(f, "a{}", self.0) } else { write!(f, "alloc{}", self.0) }
}
}
// No "Display" since AllocIds are not usually user-visible.
#[derive(TyDecodable, TyEncodable)]
enum AllocDiscriminant {
Alloc,
Fn,
VTable,
Static,
}
pub fn specialized_encode_alloc_id<'tcx, E: TyEncoder<I = TyCtxt<'tcx>>>(
encoder: &mut E,
tcx: TyCtxt<'tcx>,
alloc_id: AllocId,
) {
match tcx.global_alloc(alloc_id) {
GlobalAlloc::Memory(alloc) => {
trace!("encoding {:?} with {:#?}", alloc_id, alloc);
AllocDiscriminant::Alloc.encode(encoder);
alloc.encode(encoder);
}
GlobalAlloc::Function { instance } => {
trace!("encoding {:?} with {:#?}", alloc_id, instance);
AllocDiscriminant::Fn.encode(encoder);
instance.encode(encoder);
}
GlobalAlloc::VTable(ty, poly_trait_ref) => {
trace!("encoding {:?} with {ty:#?}, {poly_trait_ref:#?}", alloc_id);
AllocDiscriminant::VTable.encode(encoder);
ty.encode(encoder);
poly_trait_ref.encode(encoder);
}
GlobalAlloc::Static(did) => {
assert!(!tcx.is_thread_local_static(did));
// References to statics doesn't need to know about their allocations,
// just about its `DefId`.
AllocDiscriminant::Static.encode(encoder);
// Cannot use `did.encode(encoder)` because of a bug around
// specializations and method calls.
Encodable::<E>::encode(&did, encoder);
}
}
}
#[derive(Clone)]
enum State {
Empty,
Done(AllocId),
}
pub struct AllocDecodingState {
// For each `AllocId`, we keep track of which decoding state it's currently in.
decoding_state: Vec<Lock<State>>,
// The offsets of each allocation in the data stream.
data_offsets: Vec<u64>,
}
impl AllocDecodingState {
#[inline]
pub fn new_decoding_session(&self) -> AllocDecodingSession<'_> {
AllocDecodingSession { state: self }
}
pub fn new(data_offsets: Vec<u64>) -> Self {
let decoding_state =
std::iter::repeat_with(|| Lock::new(State::Empty)).take(data_offsets.len()).collect();
Self { decoding_state, data_offsets }
}
}
#[derive(Copy, Clone)]
pub struct AllocDecodingSession<'s> {
state: &'s AllocDecodingState,
}
impl<'s> AllocDecodingSession<'s> {
/// Decodes an `AllocId` in a thread-safe way.
pub fn decode_alloc_id<'tcx, D>(&self, decoder: &mut D) -> AllocId
where
D: TyDecoder<I = TyCtxt<'tcx>>,
{
// Read the index of the allocation.
let idx = usize::try_from(decoder.read_u32()).unwrap();
let pos = usize::try_from(self.state.data_offsets[idx]).unwrap();
// Decode the `AllocDiscriminant` now so that we know if we have to reserve an
// `AllocId`.
let (alloc_kind, pos) = decoder.with_position(pos, |decoder| {
let alloc_kind = AllocDiscriminant::decode(decoder);
(alloc_kind, decoder.position())
});
// We are going to hold this lock during the entire decoding of this allocation, which may
// require that we decode other allocations. This cannot deadlock for two reasons:
//
// At the time of writing, it is only possible to create an allocation that contains a pointer
// to itself using the const_allocate intrinsic (which is for testing only), and even attempting
// to evaluate such consts blows the stack. If we ever grow a mechanism for producing
// cyclic allocations, we will need a new strategy for decoding that doesn't bring back
// https://github.com/rust-lang/rust/issues/126741.
//
// It is also impossible to create two allocations (call them A and B) where A is a pointer to B, and B
// is a pointer to A, because attempting to evaluate either of those consts will produce a
// query cycle, failing compilation.
let mut entry = self.state.decoding_state[idx].lock();
// Check the decoding state to see if it's already decoded or if we should
// decode it here.
if let State::Done(alloc_id) = *entry {
return alloc_id;
}
// Now decode the actual data.
let alloc_id = decoder.with_position(pos, |decoder| match alloc_kind {
AllocDiscriminant::Alloc => {
trace!("creating memory alloc ID");
let alloc = <ConstAllocation<'tcx> as Decodable<_>>::decode(decoder);
trace!("decoded alloc {:?}", alloc);
decoder.interner().reserve_and_set_memory_alloc(alloc)
}
AllocDiscriminant::Fn => {
trace!("creating fn alloc ID");
let instance = ty::Instance::decode(decoder);
trace!("decoded fn alloc instance: {:?}", instance);
decoder.interner().reserve_and_set_fn_alloc(instance, CTFE_ALLOC_SALT)
}
AllocDiscriminant::VTable => {
trace!("creating vtable alloc ID");
let ty = Decodable::decode(decoder);
let poly_trait_ref = Decodable::decode(decoder);
trace!("decoded vtable alloc instance: {ty:?}, {poly_trait_ref:?}");
decoder.interner().reserve_and_set_vtable_alloc(ty, poly_trait_ref, CTFE_ALLOC_SALT)
}
AllocDiscriminant::Static => {
trace!("creating extern static alloc ID");
let did = <DefId as Decodable<D>>::decode(decoder);
trace!("decoded static def-ID: {:?}", did);
decoder.interner().reserve_and_set_static_alloc(did)
}
});
*entry = State::Done(alloc_id);
alloc_id
}
}
/// An allocation in the global (tcx-managed) memory can be either a function pointer,
/// a static, or a "real" allocation with some data in it.
#[derive(Debug, Clone, Eq, PartialEq, Hash, TyDecodable, TyEncodable, HashStable)]
pub enum GlobalAlloc<'tcx> {
/// The alloc ID is used as a function pointer.
Function { instance: Instance<'tcx> },
/// This alloc ID points to a symbolic (not-reified) vtable.
/// We remember the full dyn type, not just the principal trait, so that
/// const-eval and Miri can detect UB due to invalid transmutes of
/// `dyn Trait` types.
VTable(Ty<'tcx>, &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>),
/// The alloc ID points to a "lazy" static variable that did not get computed (yet).
/// This is also used to break the cycle in recursive statics.
Static(DefId),
/// The alloc ID points to memory.
Memory(ConstAllocation<'tcx>),
}
impl<'tcx> GlobalAlloc<'tcx> {
/// Panics if the `GlobalAlloc` does not refer to an `GlobalAlloc::Memory`
#[track_caller]
#[inline]
pub fn unwrap_memory(&self) -> ConstAllocation<'tcx> {
match *self {
GlobalAlloc::Memory(mem) => mem,
_ => bug!("expected memory, got {:?}", self),
}
}
/// Panics if the `GlobalAlloc` is not `GlobalAlloc::Function`
#[track_caller]
#[inline]
pub fn unwrap_fn(&self) -> Instance<'tcx> {
match *self {
GlobalAlloc::Function { instance, .. } => instance,
_ => bug!("expected function, got {:?}", self),
}
}
/// Panics if the `GlobalAlloc` is not `GlobalAlloc::VTable`
#[track_caller]
#[inline]
pub fn unwrap_vtable(&self) -> (Ty<'tcx>, Option<ty::PolyExistentialTraitRef<'tcx>>) {
match *self {
GlobalAlloc::VTable(ty, dyn_ty) => (ty, dyn_ty.principal()),
_ => bug!("expected vtable, got {:?}", self),
}
}
/// The address space that this `GlobalAlloc` should be placed in.
#[inline]
pub fn address_space(&self, cx: &impl HasDataLayout) -> AddressSpace {
match self {
GlobalAlloc::Function { .. } => cx.data_layout().instruction_address_space,
GlobalAlloc::Static(..) | GlobalAlloc::Memory(..) | GlobalAlloc::VTable(..) => {
AddressSpace::DATA
}
}
}
}
pub const CTFE_ALLOC_SALT: usize = 0;
pub(crate) struct AllocMap<'tcx> {
/// Maps `AllocId`s to their corresponding allocations.
alloc_map: FxHashMap<AllocId, GlobalAlloc<'tcx>>,
/// Used to deduplicate global allocations: functions, vtables, string literals, ...
///
/// The `usize` is a "salt" used by Miri to make deduplication imperfect, thus better emulating
/// the actual guarantees.
dedup: FxHashMap<(GlobalAlloc<'tcx>, usize), AllocId>,
/// The `AllocId` to assign to the next requested ID.
/// Always incremented; never gets smaller.
next_id: AllocId,
}
impl<'tcx> AllocMap<'tcx> {
pub(crate) fn new() -> Self {
AllocMap {
alloc_map: Default::default(),
dedup: Default::default(),
next_id: AllocId(NonZero::new(1).unwrap()),
}
}
fn reserve(&mut self) -> AllocId {
let next = self.next_id;
self.next_id.0 = self.next_id.0.checked_add(1).expect(
"You overflowed a u64 by incrementing by 1... \
You've just earned yourself a free drink if we ever meet. \
Seriously, how did you do that?!",
);
next
}
}
impl<'tcx> TyCtxt<'tcx> {
/// Obtains a new allocation ID that can be referenced but does not
/// yet have an allocation backing it.
///
/// Make sure to call `set_alloc_id_memory` or `set_alloc_id_same_memory` before returning such
/// an `AllocId` from a query.
pub fn reserve_alloc_id(self) -> AllocId {
self.alloc_map.lock().reserve()
}
/// Reserves a new ID *if* this allocation has not been dedup-reserved before.
/// Should not be used for mutable memory.
fn reserve_and_set_dedup(self, alloc: GlobalAlloc<'tcx>, salt: usize) -> AllocId {
let mut alloc_map = self.alloc_map.lock();
if let GlobalAlloc::Memory(mem) = alloc {
if mem.inner().mutability.is_mut() {
bug!("trying to dedup-reserve mutable memory");
}
}
let alloc_salt = (alloc, salt);
if let Some(&alloc_id) = alloc_map.dedup.get(&alloc_salt) {
return alloc_id;
}
let id = alloc_map.reserve();
debug!("creating alloc {:?} with id {id:?}", alloc_salt.0);
alloc_map.alloc_map.insert(id, alloc_salt.0.clone());
alloc_map.dedup.insert(alloc_salt, id);
id
}
/// Generates an `AllocId` for a memory allocation. If the exact same memory has been
/// allocated before, this will return the same `AllocId`.
pub fn reserve_and_set_memory_dedup(self, mem: ConstAllocation<'tcx>, salt: usize) -> AllocId {
self.reserve_and_set_dedup(GlobalAlloc::Memory(mem), salt)
}
/// Generates an `AllocId` for a static or return a cached one in case this function has been
/// called on the same static before.
pub fn reserve_and_set_static_alloc(self, static_id: DefId) -> AllocId {
let salt = 0; // Statics have a guaranteed unique address, no salt added.
self.reserve_and_set_dedup(GlobalAlloc::Static(static_id), salt)
}
/// Generates an `AllocId` for a function. Will get deduplicated.
pub fn reserve_and_set_fn_alloc(self, instance: Instance<'tcx>, salt: usize) -> AllocId {
self.reserve_and_set_dedup(GlobalAlloc::Function { instance }, salt)
}
/// Generates an `AllocId` for a (symbolic, not-reified) vtable. Will get deduplicated.
pub fn reserve_and_set_vtable_alloc(
self,
ty: Ty<'tcx>,
dyn_ty: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
salt: usize,
) -> AllocId {
self.reserve_and_set_dedup(GlobalAlloc::VTable(ty, dyn_ty), salt)
}
/// Interns the `Allocation` and return a new `AllocId`, even if there's already an identical
/// `Allocation` with a different `AllocId`.
/// Statics with identical content will still point to the same `Allocation`, i.e.,
/// their data will be deduplicated through `Allocation` interning -- but they
/// are different places in memory and as such need different IDs.
pub fn reserve_and_set_memory_alloc(self, mem: ConstAllocation<'tcx>) -> AllocId {
let id = self.reserve_alloc_id();
self.set_alloc_id_memory(id, mem);
id
}
/// Returns `None` in case the `AllocId` is dangling. An `InterpretCx` can still have a
/// local `Allocation` for that `AllocId`, but having such an `AllocId` in a constant is
/// illegal and will likely ICE.
/// This function exists to allow const eval to detect the difference between evaluation-
/// local dangling pointers and allocations in constants/statics.
#[inline]
pub fn try_get_global_alloc(self, id: AllocId) -> Option<GlobalAlloc<'tcx>> {
self.alloc_map.lock().alloc_map.get(&id).cloned()
}
#[inline]
#[track_caller]
/// Panics in case the `AllocId` is dangling. Since that is impossible for `AllocId`s in
/// constants (as all constants must pass interning and validation that check for dangling
/// ids), this function is frequently used throughout rustc, but should not be used within
/// the interpreter.
pub fn global_alloc(self, id: AllocId) -> GlobalAlloc<'tcx> {
match self.try_get_global_alloc(id) {
Some(alloc) => alloc,
None => bug!("could not find allocation for {id:?}"),
}
}
/// Freezes an `AllocId` created with `reserve` by pointing it at an `Allocation`. Trying to
/// call this function twice, even with the same `Allocation` will ICE the compiler.
pub fn set_alloc_id_memory(self, id: AllocId, mem: ConstAllocation<'tcx>) {
if let Some(old) = self.alloc_map.lock().alloc_map.insert(id, GlobalAlloc::Memory(mem)) {
bug!("tried to set allocation ID {id:?}, but it was already existing as {old:#?}");
}
}
/// Freezes an `AllocId` created with `reserve` by pointing it at a static item. Trying to
/// call this function twice, even with the same `DefId` will ICE the compiler.
pub fn set_nested_alloc_id_static(self, id: AllocId, def_id: LocalDefId) {
if let Some(old) =
self.alloc_map.lock().alloc_map.insert(id, GlobalAlloc::Static(def_id.to_def_id()))
{
bug!("tried to set allocation ID {id:?}, but it was already existing as {old:#?}");
}
}
}
////////////////////////////////////////////////////////////////////////////////
// Methods to access integers in the target endianness
////////////////////////////////////////////////////////////////////////////////
#[inline]
pub fn write_target_uint(
endianness: Endian,
mut target: &mut [u8],
data: u128,
) -> Result<(), io::Error> {
// This u128 holds an "any-size uint" (since smaller uints can fits in it)
// So we do not write all bytes of the u128, just the "payload".
match endianness {
Endian::Little => target.write(&data.to_le_bytes())?,
Endian::Big => target.write(&data.to_be_bytes()[16 - target.len()..])?,
};
debug_assert!(target.len() == 0); // We should have filled the target buffer.
Ok(())
}
#[inline]
pub fn read_target_uint(endianness: Endian, mut source: &[u8]) -> Result<u128, io::Error> {
// This u128 holds an "any-size uint" (since smaller uints can fits in it)
let mut buf = [0u8; std::mem::size_of::<u128>()];
// So we do not read exactly 16 bytes into the u128, just the "payload".
let uint = match endianness {
Endian::Little => {
source.read_exact(&mut buf[..source.len()])?;
Ok(u128::from_le_bytes(buf))
}
Endian::Big => {
source.read_exact(&mut buf[16 - source.len()..])?;
Ok(u128::from_be_bytes(buf))
}
};
debug_assert!(source.len() == 0); // We should have consumed the source buffer.
uint
}