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use rustc_hir::def::DefKind;
use rustc_hir::{LangItem, CRATE_HIR_ID};
use rustc_middle::mir;
use rustc_middle::mir::interpret::PointerArithmetic;
use rustc_middle::ty::layout::{FnAbiOf, TyAndLayout};
use rustc_middle::ty::{self, TyCtxt};
use rustc_session::lint::builtin::INVALID_ALIGNMENT;
use std::borrow::Borrow;
use std::hash::Hash;
use std::ops::ControlFlow;
use rustc_data_structures::fx::FxIndexMap;
use rustc_data_structures::fx::IndexEntry;
use std::fmt;
use rustc_ast::Mutability;
use rustc_hir::def_id::DefId;
use rustc_middle::mir::AssertMessage;
use rustc_span::symbol::{sym, Symbol};
use rustc_target::abi::{Align, Size};
use rustc_target::spec::abi::Abi as CallAbi;
use crate::errors::{LongRunning, LongRunningWarn};
use crate::interpret::{
self, compile_time_machine, AllocId, ConstAllocation, FnArg, FnVal, Frame, ImmTy, InterpCx,
InterpResult, OpTy, PlaceTy, Pointer, Scalar,
};
use crate::{errors, fluent_generated as fluent};
use super::error::*;
/// When hitting this many interpreted terminators we emit a deny by default lint
/// that notfies the user that their constant takes a long time to evaluate. If that's
/// what they intended, they can just allow the lint.
const LINT_TERMINATOR_LIMIT: usize = 2_000_000;
/// The limit used by `-Z tiny-const-eval-limit`. This smaller limit is useful for internal
/// tests not needing to run 30s or more to show some behaviour.
const TINY_LINT_TERMINATOR_LIMIT: usize = 20;
/// After this many interpreted terminators, we start emitting progress indicators at every
/// power of two of interpreted terminators.
const PROGRESS_INDICATOR_START: usize = 4_000_000;
/// Extra machine state for CTFE, and the Machine instance
pub struct CompileTimeInterpreter<'mir, 'tcx> {
/// The number of terminators that have been evaluated.
///
/// This is used to produce lints informing the user that the compiler is not stuck.
/// Set to `usize::MAX` to never report anything.
pub(super) num_evaluated_steps: usize,
/// The virtual call stack.
pub(super) stack: Vec<Frame<'mir, 'tcx, AllocId, ()>>,
/// We need to make sure consts never point to anything mutable, even recursively. That is
/// relied on for pattern matching on consts with references.
/// To achieve this, two pieces have to work together:
/// * Interning makes everything outside of statics immutable.
/// * Pointers to allocations inside of statics can never leak outside, to a non-static global.
/// This boolean here controls the second part.
pub(super) can_access_statics: CanAccessStatics,
/// Whether to check alignment during evaluation.
pub(super) check_alignment: CheckAlignment,
}
#[derive(Copy, Clone)]
pub enum CheckAlignment {
/// Ignore alignment when following relocations.
/// This is mainly used in interning.
No,
/// Hard error when dereferencing a misaligned pointer.
Error,
/// Emit a future incompat lint when dereferencing a misaligned pointer.
FutureIncompat,
}
impl CheckAlignment {
pub fn should_check(&self) -> bool {
match self {
CheckAlignment::No => false,
CheckAlignment::Error | CheckAlignment::FutureIncompat => true,
}
}
}
#[derive(Copy, Clone, PartialEq)]
pub(crate) enum CanAccessStatics {
No,
Yes,
}
impl From<bool> for CanAccessStatics {
fn from(value: bool) -> Self {
if value { Self::Yes } else { Self::No }
}
}
impl<'mir, 'tcx> CompileTimeInterpreter<'mir, 'tcx> {
pub(crate) fn new(
can_access_statics: CanAccessStatics,
check_alignment: CheckAlignment,
) -> Self {
CompileTimeInterpreter {
num_evaluated_steps: 0,
stack: Vec::new(),
can_access_statics,
check_alignment,
}
}
}
impl<K: Hash + Eq, V> interpret::AllocMap<K, V> for FxIndexMap<K, V> {
#[inline(always)]
fn contains_key<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> bool
where
K: Borrow<Q>,
{
FxIndexMap::contains_key(self, k)
}
#[inline(always)]
fn insert(&mut self, k: K, v: V) -> Option<V> {
FxIndexMap::insert(self, k, v)
}
#[inline(always)]
fn remove<Q: ?Sized + Hash + Eq>(&mut self, k: &Q) -> Option<V>
where
K: Borrow<Q>,
{
FxIndexMap::remove(self, k)
}
#[inline(always)]
fn filter_map_collect<T>(&self, mut f: impl FnMut(&K, &V) -> Option<T>) -> Vec<T> {
self.iter().filter_map(move |(k, v)| f(k, &*v)).collect()
}
#[inline(always)]
fn get_or<E>(&self, k: K, vacant: impl FnOnce() -> Result<V, E>) -> Result<&V, E> {
match self.get(&k) {
Some(v) => Ok(v),
None => {
vacant()?;
bug!("The CTFE machine shouldn't ever need to extend the alloc_map when reading")
}
}
}
#[inline(always)]
fn get_mut_or<E>(&mut self, k: K, vacant: impl FnOnce() -> Result<V, E>) -> Result<&mut V, E> {
match self.entry(k) {
IndexEntry::Occupied(e) => Ok(e.into_mut()),
IndexEntry::Vacant(e) => {
let v = vacant()?;
Ok(e.insert(v))
}
}
}
}
pub(crate) type CompileTimeEvalContext<'mir, 'tcx> =
InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>>;
#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub enum MemoryKind {
Heap,
}
impl fmt::Display for MemoryKind {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
MemoryKind::Heap => write!(f, "heap allocation"),
}
}
}
impl interpret::MayLeak for MemoryKind {
#[inline(always)]
fn may_leak(self) -> bool {
match self {
MemoryKind::Heap => false,
}
}
}
impl interpret::MayLeak for ! {
#[inline(always)]
fn may_leak(self) -> bool {
// `self` is uninhabited
self
}
}
impl<'mir, 'tcx: 'mir> CompileTimeEvalContext<'mir, 'tcx> {
/// "Intercept" a function call, because we have something special to do for it.
/// All `#[rustc_do_not_const_check]` functions should be hooked here.
/// If this returns `Some` function, which may be `instance` or a different function with
/// compatible arguments, then evaluation should continue with that function.
/// If this returns `None`, the function call has been handled and the function has returned.
fn hook_special_const_fn(
&mut self,
instance: ty::Instance<'tcx>,
args: &[FnArg<'tcx>],
dest: &PlaceTy<'tcx>,
ret: Option<mir::BasicBlock>,
) -> InterpResult<'tcx, Option<ty::Instance<'tcx>>> {
let def_id = instance.def_id();
if self.tcx.has_attr(def_id, sym::rustc_const_panic_str)
|| Some(def_id) == self.tcx.lang_items().begin_panic_fn()
{
let args = self.copy_fn_args(args)?;
// &str or &&str
assert!(args.len() == 1);
let mut msg_place = self.deref_pointer(&args[0])?;
while msg_place.layout.ty.is_ref() {
msg_place = self.deref_pointer(&msg_place)?;
}
let msg = Symbol::intern(self.read_str(&msg_place)?);
let span = self.find_closest_untracked_caller_location();
let (file, line, col) = self.location_triple_for_span(span);
return Err(ConstEvalErrKind::Panic { msg, file, line, col }.into());
} else if Some(def_id) == self.tcx.lang_items().panic_fmt() {
// For panic_fmt, call const_panic_fmt instead.
let const_def_id = self.tcx.require_lang_item(LangItem::ConstPanicFmt, None);
let new_instance = ty::Instance::resolve(
*self.tcx,
ty::ParamEnv::reveal_all(),
const_def_id,
instance.args,
)
.unwrap()
.unwrap();
return Ok(Some(new_instance));
} else if Some(def_id) == self.tcx.lang_items().align_offset_fn() {
let args = self.copy_fn_args(args)?;
// For align_offset, we replace the function call if the pointer has no address.
match self.align_offset(instance, &args, dest, ret)? {
ControlFlow::Continue(()) => return Ok(Some(instance)),
ControlFlow::Break(()) => return Ok(None),
}
}
Ok(Some(instance))
}
/// `align_offset(ptr, target_align)` needs special handling in const eval, because the pointer
/// may not have an address.
///
/// If `ptr` does have a known address, then we return `Continue(())` and the function call should
/// proceed as normal.
///
/// If `ptr` doesn't have an address, but its underlying allocation's alignment is at most
/// `target_align`, then we call the function again with an dummy address relative to the
/// allocation.
///
/// If `ptr` doesn't have an address and `target_align` is stricter than the underlying
/// allocation's alignment, then we return `usize::MAX` immediately.
fn align_offset(
&mut self,
instance: ty::Instance<'tcx>,
args: &[OpTy<'tcx>],
dest: &PlaceTy<'tcx>,
ret: Option<mir::BasicBlock>,
) -> InterpResult<'tcx, ControlFlow<()>> {
assert_eq!(args.len(), 2);
let ptr = self.read_pointer(&args[0])?;
let target_align = self.read_scalar(&args[1])?.to_target_usize(self)?;
if !target_align.is_power_of_two() {
throw_ub_custom!(
fluent::const_eval_align_offset_invalid_align,
target_align = target_align,
);
}
match self.ptr_try_get_alloc_id(ptr) {
Ok((alloc_id, offset, _extra)) => {
let (_size, alloc_align, _kind) = self.get_alloc_info(alloc_id);
if target_align <= alloc_align.bytes() {
// Extract the address relative to the allocation base that is definitely
// sufficiently aligned and call `align_offset` again.
let addr = ImmTy::from_uint(offset.bytes(), args[0].layout).into();
let align = ImmTy::from_uint(target_align, args[1].layout).into();
let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty())?;
// We replace the entire function call with a "tail call".
// Note that this happens before the frame of the original function
// is pushed on the stack.
self.eval_fn_call(
FnVal::Instance(instance),
(CallAbi::Rust, fn_abi),
&[FnArg::Copy(addr), FnArg::Copy(align)],
/* with_caller_location = */ false,
dest,
ret,
mir::UnwindAction::Unreachable,
)?;
Ok(ControlFlow::Break(()))
} else {
// Not alignable in const, return `usize::MAX`.
let usize_max = Scalar::from_target_usize(self.target_usize_max(), self);
self.write_scalar(usize_max, dest)?;
self.return_to_block(ret)?;
Ok(ControlFlow::Break(()))
}
}
Err(_addr) => {
// The pointer has an address, continue with function call.
Ok(ControlFlow::Continue(()))
}
}
}
/// See documentation on the `ptr_guaranteed_cmp` intrinsic.
fn guaranteed_cmp(&mut self, a: Scalar, b: Scalar) -> InterpResult<'tcx, u8> {
Ok(match (a, b) {
// Comparisons between integers are always known.
(Scalar::Int { .. }, Scalar::Int { .. }) => {
if a == b {
1
} else {
0
}
}
// Comparisons of abstract pointers with null pointers are known if the pointer
// is in bounds, because if they are in bounds, the pointer can't be null.
// Inequality with integers other than null can never be known for sure.
(Scalar::Int(int), ptr @ Scalar::Ptr(..))
| (ptr @ Scalar::Ptr(..), Scalar::Int(int))
if int.is_null() && !self.scalar_may_be_null(ptr)? =>
{
0
}
// Equality with integers can never be known for sure.
(Scalar::Int { .. }, Scalar::Ptr(..)) | (Scalar::Ptr(..), Scalar::Int { .. }) => 2,
// FIXME: return a `1` for when both sides are the same pointer, *except* that
// some things (like functions and vtables) do not have stable addresses
// so we need to be careful around them (see e.g. #73722).
// FIXME: return `0` for at least some comparisons where we can reliably
// determine the result of runtime inequality tests at compile-time.
// Examples include comparison of addresses in different static items.
(Scalar::Ptr(..), Scalar::Ptr(..)) => 2,
})
}
}
impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir, 'tcx> {
compile_time_machine!(<'mir, 'tcx>);
type MemoryKind = MemoryKind;
const PANIC_ON_ALLOC_FAIL: bool = false; // will be raised as a proper error
#[inline(always)]
fn enforce_alignment(ecx: &InterpCx<'mir, 'tcx, Self>) -> CheckAlignment {
ecx.machine.check_alignment
}
#[inline(always)]
fn enforce_validity(ecx: &InterpCx<'mir, 'tcx, Self>, layout: TyAndLayout<'tcx>) -> bool {
ecx.tcx.sess.opts.unstable_opts.extra_const_ub_checks || layout.abi.is_uninhabited()
}
fn alignment_check_failed(
ecx: &InterpCx<'mir, 'tcx, Self>,
has: Align,
required: Align,
check: CheckAlignment,
) -> InterpResult<'tcx, ()> {
let err = err_ub!(AlignmentCheckFailed { has, required }).into();
match check {
CheckAlignment::Error => Err(err),
CheckAlignment::No => span_bug!(
ecx.cur_span(),
"`alignment_check_failed` called when no alignment check requested"
),
CheckAlignment::FutureIncompat => {
let (_, backtrace) = err.into_parts();
backtrace.print_backtrace();
let (span, frames) = super::get_span_and_frames(&ecx);
ecx.tcx.emit_spanned_lint(
INVALID_ALIGNMENT,
ecx.stack().iter().find_map(|frame| frame.lint_root()).unwrap_or(CRATE_HIR_ID),
span,
errors::AlignmentCheckFailed {
has: has.bytes(),
required: required.bytes(),
frames,
},
);
Ok(())
}
}
}
fn load_mir(
ecx: &InterpCx<'mir, 'tcx, Self>,
instance: ty::InstanceDef<'tcx>,
) -> InterpResult<'tcx, &'tcx mir::Body<'tcx>> {
match instance {
ty::InstanceDef::Item(def) => {
if ecx.tcx.is_ctfe_mir_available(def) {
Ok(ecx.tcx.mir_for_ctfe(def))
} else if ecx.tcx.def_kind(def) == DefKind::AssocConst {
let guar = ecx.tcx.sess.delay_span_bug(
rustc_span::DUMMY_SP,
"This is likely a const item that is missing from its impl",
);
throw_inval!(AlreadyReported(guar.into()));
} else {
// `find_mir_or_eval_fn` checks that this is a const fn before even calling us,
// so this should be unreachable.
let path = ecx.tcx.def_path_str(def);
bug!("trying to call extern function `{path}` at compile-time");
}
}
_ => Ok(ecx.tcx.instance_mir(instance)),
}
}
fn find_mir_or_eval_fn(
ecx: &mut InterpCx<'mir, 'tcx, Self>,
orig_instance: ty::Instance<'tcx>,
_abi: CallAbi,
args: &[FnArg<'tcx>],
dest: &PlaceTy<'tcx>,
ret: Option<mir::BasicBlock>,
_unwind: mir::UnwindAction, // unwinding is not supported in consts
) -> InterpResult<'tcx, Option<(&'mir mir::Body<'tcx>, ty::Instance<'tcx>)>> {
debug!("find_mir_or_eval_fn: {:?}", orig_instance);
// Replace some functions.
let Some(instance) = ecx.hook_special_const_fn(orig_instance, args, dest, ret)? else {
// Call has already been handled.
return Ok(None);
};
// Only check non-glue functions
if let ty::InstanceDef::Item(def) = instance.def {
// Execution might have wandered off into other crates, so we cannot do a stability-
// sensitive check here. But we can at least rule out functions that are not const at
// all. That said, we have to allow calling functions inside a trait marked with
// #[const_trait]. These *are* const-checked!
// FIXME: why does `is_const_fn_raw` not classify them as const?
if (!ecx.tcx.is_const_fn_raw(def) && !ecx.tcx.is_const_default_method(def))
|| ecx.tcx.has_attr(def, sym::rustc_do_not_const_check)
{
// We certainly do *not* want to actually call the fn
// though, so be sure we return here.
throw_unsup_format!("calling non-const function `{}`", instance)
}
}
// This is a const fn. Call it.
// In case of replacement, we return the *original* instance to make backtraces work out
// (and we hope this does not confuse the FnAbi checks too much).
Ok(Some((ecx.load_mir(instance.def, None)?, orig_instance)))
}
fn panic_nounwind(ecx: &mut InterpCx<'mir, 'tcx, Self>, msg: &str) -> InterpResult<'tcx> {
let msg = Symbol::intern(msg);
let span = ecx.find_closest_untracked_caller_location();
let (file, line, col) = ecx.location_triple_for_span(span);
Err(ConstEvalErrKind::Panic { msg, file, line, col }.into())
}
fn call_intrinsic(
ecx: &mut InterpCx<'mir, 'tcx, Self>,
instance: ty::Instance<'tcx>,
args: &[OpTy<'tcx>],
dest: &PlaceTy<'tcx, Self::Provenance>,
target: Option<mir::BasicBlock>,
_unwind: mir::UnwindAction,
) -> InterpResult<'tcx> {
// Shared intrinsics.
if ecx.emulate_intrinsic(instance, args, dest, target)? {
return Ok(());
}
let intrinsic_name = ecx.tcx.item_name(instance.def_id());
// CTFE-specific intrinsics.
let Some(ret) = target else {
throw_unsup_format!("intrinsic `{intrinsic_name}` is not supported at compile-time");
};
match intrinsic_name {
sym::ptr_guaranteed_cmp => {
let a = ecx.read_scalar(&args[0])?;
let b = ecx.read_scalar(&args[1])?;
let cmp = ecx.guaranteed_cmp(a, b)?;
ecx.write_scalar(Scalar::from_u8(cmp), dest)?;
}
sym::const_allocate => {
let size = ecx.read_scalar(&args[0])?.to_target_usize(ecx)?;
let align = ecx.read_scalar(&args[1])?.to_target_usize(ecx)?;
let align = match Align::from_bytes(align) {
Ok(a) => a,
Err(err) => throw_ub_custom!(
fluent::const_eval_invalid_align_details,
name = "const_allocate",
err_kind = err.diag_ident(),
align = err.align()
),
};
let ptr = ecx.allocate_ptr(
Size::from_bytes(size as u64),
align,
interpret::MemoryKind::Machine(MemoryKind::Heap),
)?;
ecx.write_pointer(ptr, dest)?;
}
sym::const_deallocate => {
let ptr = ecx.read_pointer(&args[0])?;
let size = ecx.read_scalar(&args[1])?.to_target_usize(ecx)?;
let align = ecx.read_scalar(&args[2])?.to_target_usize(ecx)?;
let size = Size::from_bytes(size);
let align = match Align::from_bytes(align) {
Ok(a) => a,
Err(err) => throw_ub_custom!(
fluent::const_eval_invalid_align_details,
name = "const_deallocate",
err_kind = err.diag_ident(),
align = err.align()
),
};
// If an allocation is created in an another const,
// we don't deallocate it.
let (alloc_id, _, _) = ecx.ptr_get_alloc_id(ptr)?;
let is_allocated_in_another_const = matches!(
ecx.tcx.try_get_global_alloc(alloc_id),
Some(interpret::GlobalAlloc::Memory(_))
);
if !is_allocated_in_another_const {
ecx.deallocate_ptr(
ptr,
Some((size, align)),
interpret::MemoryKind::Machine(MemoryKind::Heap),
)?;
}
}
_ => {
throw_unsup_format!(
"intrinsic `{intrinsic_name}` is not supported at compile-time"
);
}
}
ecx.go_to_block(ret);
Ok(())
}
fn assert_panic(
ecx: &mut InterpCx<'mir, 'tcx, Self>,
msg: &AssertMessage<'tcx>,
_unwind: mir::UnwindAction,
) -> InterpResult<'tcx> {
use rustc_middle::mir::AssertKind::*;
// Convert `AssertKind<Operand>` to `AssertKind<Scalar>`.
let eval_to_int =
|op| ecx.read_immediate(&ecx.eval_operand(op, None)?).map(|x| x.to_const_int());
let err = match msg {
BoundsCheck { len, index } => {
let len = eval_to_int(len)?;
let index = eval_to_int(index)?;
BoundsCheck { len, index }
}
Overflow(op, l, r) => Overflow(*op, eval_to_int(l)?, eval_to_int(r)?),
OverflowNeg(op) => OverflowNeg(eval_to_int(op)?),
DivisionByZero(op) => DivisionByZero(eval_to_int(op)?),
RemainderByZero(op) => RemainderByZero(eval_to_int(op)?),
ResumedAfterReturn(generator_kind) => ResumedAfterReturn(*generator_kind),
ResumedAfterPanic(generator_kind) => ResumedAfterPanic(*generator_kind),
MisalignedPointerDereference { ref required, ref found } => {
MisalignedPointerDereference {
required: eval_to_int(required)?,
found: eval_to_int(found)?,
}
}
};
Err(ConstEvalErrKind::AssertFailure(err).into())
}
fn binary_ptr_op(
_ecx: &InterpCx<'mir, 'tcx, Self>,
_bin_op: mir::BinOp,
_left: &ImmTy<'tcx>,
_right: &ImmTy<'tcx>,
) -> InterpResult<'tcx, (ImmTy<'tcx>, bool)> {
throw_unsup_format!("pointer arithmetic or comparison is not supported at compile-time");
}
fn increment_const_eval_counter(ecx: &mut InterpCx<'mir, 'tcx, Self>) -> InterpResult<'tcx> {
// The step limit has already been hit in a previous call to `increment_const_eval_counter`.
if let Some(new_steps) = ecx.machine.num_evaluated_steps.checked_add(1) {
let (limit, start) = if ecx.tcx.sess.opts.unstable_opts.tiny_const_eval_limit {
(TINY_LINT_TERMINATOR_LIMIT, TINY_LINT_TERMINATOR_LIMIT)
} else {
(LINT_TERMINATOR_LIMIT, PROGRESS_INDICATOR_START)
};
ecx.machine.num_evaluated_steps = new_steps;
// By default, we have a *deny* lint kicking in after some time
// to ensure `loop {}` doesn't just go forever.
// In case that lint got reduced, in particular for `--cap-lint` situations, we also
// have a hard warning shown every now and then for really long executions.
if new_steps == limit {
// By default, we stop after a million steps, but the user can disable this lint
// to be able to run until the heat death of the universe or power loss, whichever
// comes first.
let hir_id = ecx.best_lint_scope();
let is_error = ecx
.tcx
.lint_level_at_node(
rustc_session::lint::builtin::LONG_RUNNING_CONST_EVAL,
hir_id,
)
.0
.is_error();
let span = ecx.cur_span();
ecx.tcx.emit_spanned_lint(
rustc_session::lint::builtin::LONG_RUNNING_CONST_EVAL,
hir_id,
span,
LongRunning { item_span: ecx.tcx.span },
);
// If this was a hard error, don't bother continuing evaluation.
if is_error {
let guard = ecx
.tcx
.sess
.delay_span_bug(span, "The deny lint should have already errored");
throw_inval!(AlreadyReported(guard.into()));
}
} else if new_steps > start && new_steps.is_power_of_two() {
// Only report after a certain number of terminators have been evaluated and the
// current number of evaluated terminators is a power of 2. The latter gives us a cheap
// way to implement exponential backoff.
let span = ecx.cur_span();
ecx.tcx.sess.emit_warning(LongRunningWarn { span, item_span: ecx.tcx.span });
}
}
Ok(())
}
#[inline(always)]
fn expose_ptr(
_ecx: &mut InterpCx<'mir, 'tcx, Self>,
_ptr: Pointer<AllocId>,
) -> InterpResult<'tcx> {
// This is only reachable with -Zunleash-the-miri-inside-of-you.
throw_unsup_format!("exposing pointers is not possible at compile-time")
}
#[inline(always)]
fn init_frame_extra(
ecx: &mut InterpCx<'mir, 'tcx, Self>,
frame: Frame<'mir, 'tcx>,
) -> InterpResult<'tcx, Frame<'mir, 'tcx>> {
// Enforce stack size limit. Add 1 because this is run before the new frame is pushed.
if !ecx.recursion_limit.value_within_limit(ecx.stack().len() + 1) {
throw_exhaust!(StackFrameLimitReached)
} else {
Ok(frame)
}
}
#[inline(always)]
fn stack<'a>(
ecx: &'a InterpCx<'mir, 'tcx, Self>,
) -> &'a [Frame<'mir, 'tcx, Self::Provenance, Self::FrameExtra>] {
&ecx.machine.stack
}
#[inline(always)]
fn stack_mut<'a>(
ecx: &'a mut InterpCx<'mir, 'tcx, Self>,
) -> &'a mut Vec<Frame<'mir, 'tcx, Self::Provenance, Self::FrameExtra>> {
&mut ecx.machine.stack
}
fn before_access_global(
_tcx: TyCtxt<'tcx>,
machine: &Self,
alloc_id: AllocId,
alloc: ConstAllocation<'tcx>,
static_def_id: Option<DefId>,
is_write: bool,
) -> InterpResult<'tcx> {
let alloc = alloc.inner();
if is_write {
// Write access. These are never allowed, but we give a targeted error message.
match alloc.mutability {
Mutability::Not => Err(err_ub!(WriteToReadOnly(alloc_id)).into()),
Mutability::Mut => Err(ConstEvalErrKind::ModifiedGlobal.into()),
}
} else {
// Read access. These are usually allowed, with some exceptions.
if machine.can_access_statics == CanAccessStatics::Yes {
// Machine configuration allows us read from anything (e.g., `static` initializer).
Ok(())
} else if static_def_id.is_some() {
// Machine configuration does not allow us to read statics
// (e.g., `const` initializer).
// See const_eval::machine::MemoryExtra::can_access_statics for why
// this check is so important: if we could read statics, we could read pointers
// to mutable allocations *inside* statics. These allocations are not themselves
// statics, so pointers to them can get around the check in `validity.rs`.
Err(ConstEvalErrKind::ConstAccessesStatic.into())
} else {
// Immutable global, this read is fine.
// But make sure we never accept a read from something mutable, that would be
// unsound. The reason is that as the content of this allocation may be different
// now and at run-time, so if we permit reading now we might return the wrong value.
assert_eq!(alloc.mutability, Mutability::Not);
Ok(())
}
}
}
}
// Please do not add any code below the above `Machine` trait impl. I (oli-obk) plan more cleanups
// so we can end up having a file with just that impl, but for now, let's keep the impl discoverable
// at the bottom of this file.