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//! Transforms instances and types for LLVM CFI and cross-language LLVM CFI support using Itanium
//! C++ ABI mangling.
//!
//! For more information about LLVM CFI and cross-language LLVM CFI support for the Rust compiler,
//! see design document in the tracking issue #89653.
use rustc_hir as hir;
use rustc_hir::LangItem;
use rustc_middle::bug;
use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
use rustc_middle::ty::{
self, Instance, IntTy, List, Ty, TyCtxt, TypeFoldable, TypeVisitableExt, UintTy,
};
use rustc_span::sym;
use rustc_trait_selection::traits;
use std::iter;
use tracing::{debug, instrument};
use crate::cfi::typeid::itanium_cxx_abi::encode::EncodeTyOptions;
use crate::cfi::typeid::TypeIdOptions;
/// Options for transform_ty.
pub type TransformTyOptions = TypeIdOptions;
pub struct TransformTy<'tcx> {
tcx: TyCtxt<'tcx>,
options: TransformTyOptions,
parents: Vec<Ty<'tcx>>,
}
impl<'tcx> TransformTy<'tcx> {
pub fn new(tcx: TyCtxt<'tcx>, options: TransformTyOptions) -> Self {
TransformTy { tcx, options, parents: Vec::new() }
}
}
/// Transforms a ty:Ty for being encoded and used in the substitution dictionary.
///
/// * Transforms all c_void types into unit types.
/// * Generalizes pointers if TransformTyOptions::GENERALIZE_POINTERS option is set.
/// * Normalizes integers if TransformTyOptions::NORMALIZE_INTEGERS option is set.
/// * Generalizes any repr(transparent) user-defined type that is either a pointer or reference, and
/// either references itself or any other type that contains or references itself, to avoid a
/// reference cycle.
/// * Transforms repr(transparent) types without non-ZST field into ().
///
impl<'tcx> TypeFolder<TyCtxt<'tcx>> for TransformTy<'tcx> {
// Transforms a ty:Ty for being encoded and used in the substitution dictionary.
fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
match t.kind() {
ty::Array(..)
| ty::Closure(..)
| ty::Coroutine(..)
| ty::CoroutineClosure(..)
| ty::CoroutineWitness(..)
| ty::Dynamic(..)
| ty::Float(..)
| ty::FnDef(..)
| ty::Foreign(..)
| ty::Never
| ty::Pat(..)
| ty::Slice(..)
| ty::Str
| ty::Tuple(..) => t.super_fold_with(self),
ty::Bool => {
if self.options.contains(EncodeTyOptions::NORMALIZE_INTEGERS) {
// Note: on all platforms that Rust's currently supports, its size and alignment
// are 1, and its ABI class is INTEGER - see Rust Layout and ABIs.
//
// (See https://rust-lang.github.io/unsafe-code-guidelines/layout/scalars.html#bool.)
//
// Clang represents bool as an 8-bit unsigned integer.
self.tcx.types.u8
} else {
t
}
}
ty::Char => {
if self.options.contains(EncodeTyOptions::NORMALIZE_INTEGERS) {
// Since #118032, char is guaranteed to have the same size, alignment, and
// function call ABI as u32 on all platforms.
self.tcx.types.u32
} else {
t
}
}
ty::Int(..) | ty::Uint(..) => {
if self.options.contains(EncodeTyOptions::NORMALIZE_INTEGERS) {
// Note: C99 7.18.2.4 requires uintptr_t and intptr_t to be at least 16-bit
// wide. All platforms we currently support have a C platform, and as a
// consequence, isize/usize are at least 16-bit wide for all of them.
//
// (See https://rust-lang.github.io/unsafe-code-guidelines/layout/scalars.html#isize-and-usize.)
match t.kind() {
ty::Int(IntTy::Isize) => match self.tcx.sess.target.pointer_width {
16 => self.tcx.types.i16,
32 => self.tcx.types.i32,
64 => self.tcx.types.i64,
128 => self.tcx.types.i128,
_ => bug!(
"fold_ty: unexpected pointer width `{}`",
self.tcx.sess.target.pointer_width
),
},
ty::Uint(UintTy::Usize) => match self.tcx.sess.target.pointer_width {
16 => self.tcx.types.u16,
32 => self.tcx.types.u32,
64 => self.tcx.types.u64,
128 => self.tcx.types.u128,
_ => bug!(
"fold_ty: unexpected pointer width `{}`",
self.tcx.sess.target.pointer_width
),
},
_ => t,
}
} else {
t
}
}
ty::Adt(..) if t.is_c_void(self.tcx) => self.tcx.types.unit,
ty::Adt(adt_def, args) => {
if adt_def.repr().transparent() && adt_def.is_struct() && !self.parents.contains(&t)
{
// Don't transform repr(transparent) types with an user-defined CFI encoding to
// preserve the user-defined CFI encoding.
if let Some(_) = self.tcx.get_attr(adt_def.did(), sym::cfi_encoding) {
return t;
}
let variant = adt_def.non_enum_variant();
let param_env = self.tcx.param_env(variant.def_id);
let field = variant.fields.iter().find(|field| {
let ty = self.tcx.type_of(field.did).instantiate_identity();
let is_zst = self
.tcx
.layout_of(param_env.and(ty))
.is_ok_and(|layout| layout.is_zst());
!is_zst
});
if let Some(field) = field {
let ty0 = self.tcx.type_of(field.did).instantiate(self.tcx, args);
// Generalize any repr(transparent) user-defined type that is either a
// pointer or reference, and either references itself or any other type that
// contains or references itself, to avoid a reference cycle.
// If the self reference is not through a pointer, for example, due
// to using `PhantomData`, need to skip normalizing it if we hit it again.
self.parents.push(t);
let ty = if ty0.is_any_ptr() && ty0.contains(t) {
let options = self.options;
self.options |= TransformTyOptions::GENERALIZE_POINTERS;
let ty = ty0.fold_with(self);
self.options = options;
ty
} else {
ty0.fold_with(self)
};
self.parents.pop();
ty
} else {
// Transform repr(transparent) types without non-ZST field into ()
self.tcx.types.unit
}
} else {
t.super_fold_with(self)
}
}
ty::Ref(..) => {
if self.options.contains(TransformTyOptions::GENERALIZE_POINTERS) {
if t.is_mutable_ptr() {
Ty::new_mut_ref(self.tcx, self.tcx.lifetimes.re_static, self.tcx.types.unit)
} else {
Ty::new_imm_ref(self.tcx, self.tcx.lifetimes.re_static, self.tcx.types.unit)
}
} else {
t.super_fold_with(self)
}
}
ty::RawPtr(..) => {
if self.options.contains(TransformTyOptions::GENERALIZE_POINTERS) {
if t.is_mutable_ptr() {
Ty::new_mut_ptr(self.tcx, self.tcx.types.unit)
} else {
Ty::new_imm_ptr(self.tcx, self.tcx.types.unit)
}
} else {
t.super_fold_with(self)
}
}
ty::FnPtr(..) => {
if self.options.contains(TransformTyOptions::GENERALIZE_POINTERS) {
Ty::new_imm_ptr(self.tcx, self.tcx.types.unit)
} else {
t.super_fold_with(self)
}
}
ty::Alias(..) => {
self.fold_ty(self.tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), t))
}
ty::Bound(..) | ty::Error(..) | ty::Infer(..) | ty::Param(..) | ty::Placeholder(..) => {
bug!("fold_ty: unexpected `{:?}`", t.kind());
}
}
}
fn interner(&self) -> TyCtxt<'tcx> {
self.tcx
}
}
#[instrument(skip(tcx), ret)]
fn trait_object_ty<'tcx>(tcx: TyCtxt<'tcx>, poly_trait_ref: ty::PolyTraitRef<'tcx>) -> Ty<'tcx> {
assert!(!poly_trait_ref.has_non_region_param());
let principal_pred = poly_trait_ref.map_bound(|trait_ref| {
ty::ExistentialPredicate::Trait(ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref))
});
let mut assoc_preds: Vec<_> = traits::supertraits(tcx, poly_trait_ref)
.flat_map(|super_poly_trait_ref| {
tcx.associated_items(super_poly_trait_ref.def_id())
.in_definition_order()
.filter(|item| item.kind == ty::AssocKind::Type)
.map(move |assoc_ty| {
super_poly_trait_ref.map_bound(|super_trait_ref| {
let alias_ty = ty::AliasTy::new(tcx, assoc_ty.def_id, super_trait_ref.args);
let resolved = tcx.normalize_erasing_regions(
ty::ParamEnv::reveal_all(),
alias_ty.to_ty(tcx),
);
debug!("Resolved {:?} -> {resolved}", alias_ty.to_ty(tcx));
ty::ExistentialPredicate::Projection(ty::ExistentialProjection {
def_id: assoc_ty.def_id,
args: ty::ExistentialTraitRef::erase_self_ty(tcx, super_trait_ref).args,
term: resolved.into(),
})
})
})
})
.collect();
assoc_preds.sort_by(|a, b| a.skip_binder().stable_cmp(tcx, &b.skip_binder()));
let preds = tcx.mk_poly_existential_predicates_from_iter(
iter::once(principal_pred).chain(assoc_preds.into_iter()),
);
Ty::new_dynamic(tcx, preds, tcx.lifetimes.re_erased, ty::Dyn)
}
/// Transforms an instance for LLVM CFI and cross-language LLVM CFI support using Itanium C++ ABI
/// mangling.
///
/// typeid_for_instance is called at two locations, initially when declaring/defining functions and
/// methods, and later during code generation at call sites, after type erasure might have ocurred.
///
/// In the first call (i.e., when declaring/defining functions and methods), it encodes type ids for
/// an FnAbi or Instance, and these type ids are attached to functions and methods. (These type ids
/// are used later by the LowerTypeTests LLVM pass to aggregate functions in groups derived from
/// these type ids.)
///
/// In the second call (i.e., during code generation at call sites), it encodes a type id for an
/// FnAbi or Instance, after type erasure might have occured, and this type id is used for testing
/// if a function is member of the group derived from this type id. Therefore, in the first call to
/// typeid_for_fnabi (when type ids are attached to functions and methods), it can only include at
/// most as much information that would be available in the second call (i.e., during code
/// generation at call sites); otherwise, the type ids would not not match.
///
/// For this, it:
///
/// * Adjust the type ids of DropGlues (see below).
/// * Adjusts the type ids of VTableShims to the type id expected in the call sites for the
/// entry in the vtable (i.e., by using the signature of the closure passed as an argument to the
/// shim, or by just removing self).
/// * Performs type erasure for calls on trait objects by transforming self into a trait object of
/// the trait that defines the method.
/// * Performs type erasure for closures call methods by transforming self into a trait object of
/// the Fn trait that defines the method (for being attached as a secondary type id).
///
#[instrument(level = "trace", skip(tcx))]
pub fn transform_instance<'tcx>(
tcx: TyCtxt<'tcx>,
mut instance: Instance<'tcx>,
options: TransformTyOptions,
) -> Instance<'tcx> {
if (matches!(instance.def, ty::InstanceDef::Virtual(..))
&& Some(instance.def_id()) == tcx.lang_items().drop_in_place_fn())
|| matches!(instance.def, ty::InstanceDef::DropGlue(..))
{
// Adjust the type ids of DropGlues
//
// DropGlues may have indirect calls to one or more given types drop function. Rust allows
// for types to be erased to any trait object and retains the drop function for the original
// type, which means at the indirect call sites in DropGlues, when typeid_for_fnabi is
// called a second time, it only has information after type erasure and it could be a call
// on any arbitrary trait object. Normalize them to a synthesized Drop trait object, both on
// declaration/definition, and during code generation at call sites so they have the same
// type id and match.
//
// FIXME(rcvalle): This allows a drop call on any trait object to call the drop function of
// any other type.
//
let def_id = tcx
.lang_items()
.drop_trait()
.unwrap_or_else(|| bug!("typeid_for_instance: couldn't get drop_trait lang item"));
let predicate = ty::ExistentialPredicate::Trait(ty::ExistentialTraitRef {
def_id: def_id,
args: List::empty(),
});
let predicates = tcx.mk_poly_existential_predicates(&[ty::Binder::dummy(predicate)]);
let self_ty = Ty::new_dynamic(tcx, predicates, tcx.lifetimes.re_erased, ty::Dyn);
instance.args = tcx.mk_args_trait(self_ty, List::empty());
} else if let ty::InstanceDef::Virtual(def_id, _) = instance.def {
// Transform self into a trait object of the trait that defines the method for virtual
// functions to match the type erasure done below.
let upcast_ty = match tcx.trait_of_item(def_id) {
Some(trait_id) => trait_object_ty(
tcx,
ty::Binder::dummy(ty::TraitRef::from_method(tcx, trait_id, instance.args)),
),
// drop_in_place won't have a defining trait, skip the upcast
None => instance.args.type_at(0),
};
let ty::Dynamic(preds, lifetime, kind) = upcast_ty.kind() else {
bug!("Tried to remove autotraits from non-dynamic type {upcast_ty}");
};
let self_ty = if preds.principal().is_some() {
let filtered_preds =
tcx.mk_poly_existential_predicates_from_iter(preds.into_iter().filter(|pred| {
!matches!(pred.skip_binder(), ty::ExistentialPredicate::AutoTrait(..))
}));
Ty::new_dynamic(tcx, filtered_preds, *lifetime, *kind)
} else {
// If there's no principal type, re-encode it as a unit, since we don't know anything
// about it. This technically discards the knowledge that it was a type that was made
// into a trait object at some point, but that's not a lot.
tcx.types.unit
};
instance.args = tcx.mk_args_trait(self_ty, instance.args.into_iter().skip(1));
} else if let ty::InstanceDef::VTableShim(def_id) = instance.def
&& let Some(trait_id) = tcx.trait_of_item(def_id)
{
// Adjust the type ids of VTableShims to the type id expected in the call sites for the
// entry in the vtable (i.e., by using the signature of the closure passed as an argument
// to the shim, or by just removing self).
let trait_ref = ty::TraitRef::new(tcx, trait_id, instance.args);
let invoke_ty = trait_object_ty(tcx, ty::Binder::dummy(trait_ref));
instance.args = tcx.mk_args_trait(invoke_ty, trait_ref.args.into_iter().skip(1));
}
if !options.contains(TransformTyOptions::USE_CONCRETE_SELF) {
// Perform type erasure for calls on trait objects by transforming self into a trait object
// of the trait that defines the method.
if let Some(impl_id) = tcx.impl_of_method(instance.def_id())
&& let Some(trait_ref) = tcx.impl_trait_ref(impl_id)
{
let impl_method = tcx.associated_item(instance.def_id());
let method_id = impl_method
.trait_item_def_id
.expect("Part of a trait implementation, but not linked to the def_id?");
let trait_method = tcx.associated_item(method_id);
let trait_id = trait_ref.skip_binder().def_id;
if traits::is_vtable_safe_method(tcx, trait_id, trait_method)
&& tcx.object_safety_violations(trait_id).is_empty()
{
// Trait methods will have a Self polymorphic parameter, where the concreteized
// implementatation will not. We need to walk back to the more general trait method
let trait_ref = tcx.instantiate_and_normalize_erasing_regions(
instance.args,
ty::ParamEnv::reveal_all(),
trait_ref,
);
let invoke_ty = trait_object_ty(tcx, ty::Binder::dummy(trait_ref));
// At the call site, any call to this concrete function through a vtable will be
// `Virtual(method_id, idx)` with appropriate arguments for the method. Since we have the
// original method id, and we've recovered the trait arguments, we can make the callee
// instance we're computing the alias set for match the caller instance.
//
// Right now, our code ignores the vtable index everywhere, so we use 0 as a placeholder.
// If we ever *do* start encoding the vtable index, we will need to generate an alias set
// based on which vtables we are putting this method into, as there will be more than one
// index value when supertraits are involved.
instance.def = ty::InstanceDef::Virtual(method_id, 0);
let abstract_trait_args =
tcx.mk_args_trait(invoke_ty, trait_ref.args.into_iter().skip(1));
instance.args = instance.args.rebase_onto(tcx, impl_id, abstract_trait_args);
}
} else if tcx.is_closure_like(instance.def_id()) {
// We're either a closure or a coroutine. Our goal is to find the trait we're defined on,
// instantiate it, and take the type of its only method as our own.
let closure_ty = instance.ty(tcx, ty::ParamEnv::reveal_all());
let (trait_id, inputs) = match closure_ty.kind() {
ty::Closure(..) => {
let closure_args = instance.args.as_closure();
let trait_id = tcx.fn_trait_kind_to_def_id(closure_args.kind()).unwrap();
let tuple_args =
tcx.instantiate_bound_regions_with_erased(closure_args.sig()).inputs()[0];
(trait_id, Some(tuple_args))
}
ty::Coroutine(..) => match tcx.coroutine_kind(instance.def_id()).unwrap() {
hir::CoroutineKind::Coroutine(..) => (
tcx.require_lang_item(LangItem::Coroutine, None),
Some(instance.args.as_coroutine().resume_ty()),
),
hir::CoroutineKind::Desugared(desugaring, _) => {
let lang_item = match desugaring {
hir::CoroutineDesugaring::Async => LangItem::Future,
hir::CoroutineDesugaring::AsyncGen => LangItem::AsyncIterator,
hir::CoroutineDesugaring::Gen => LangItem::Iterator,
};
(tcx.require_lang_item(lang_item, None), None)
}
},
ty::CoroutineClosure(..) => (
tcx.require_lang_item(LangItem::FnOnce, None),
Some(
tcx.instantiate_bound_regions_with_erased(
instance.args.as_coroutine_closure().coroutine_closure_sig(),
)
.tupled_inputs_ty,
),
),
x => bug!("Unexpected type kind for closure-like: {x:?}"),
};
let concrete_args = tcx.mk_args_trait(closure_ty, inputs.map(Into::into));
let trait_ref = ty::TraitRef::new(tcx, trait_id, concrete_args);
let invoke_ty = trait_object_ty(tcx, ty::Binder::dummy(trait_ref));
let abstract_args = tcx.mk_args_trait(invoke_ty, trait_ref.args.into_iter().skip(1));
// There should be exactly one method on this trait, and it should be the one we're
// defining.
let call = tcx
.associated_items(trait_id)
.in_definition_order()
.find(|it| it.kind == ty::AssocKind::Fn)
.expect("No call-family function on closure-like Fn trait?")
.def_id;
instance.def = ty::InstanceDef::Virtual(call, 0);
instance.args = abstract_args;
}
}
instance
}