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CFI: Support self_cell-like recursion
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Current `transform_ty` attempts to avoid cycles when normalizing
`#[repr(transparent)]` types to their interior, but runs afoul of this
pattern used in `self_cell`:

```
struct X<T> {
  x: u8,
  p: PhantomData<T>,
}

 #[repr(transparent)]
struct Y(X<Y>);
```

When attempting to normalize Y, it will still cycle indefinitely. By
using a types-visited list, this will instead get expanded exactly
one layer deep to X<Y>, and then stop, not attempting to normalize `Y`
any further.
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@maurer
maurer committed Mar 4, 2024
1 parent fa04e3b commit 5ec1ec4
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Showing 2 changed files with 75 additions and 25 deletions.
69 changes: 44 additions & 25 deletions compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -178,14 +178,14 @@ fn encode_fnsig<'tcx>(
// Encode the return type
let transform_ty_options = TransformTyOptions::from_bits(options.bits())
.unwrap_or_else(|| bug!("encode_fnsig: invalid option(s) `{:?}`", options.bits()));
let ty = transform_ty(tcx, fn_sig.output(), transform_ty_options);
let ty = transform_ty(tcx, fn_sig.output(), &[], transform_ty_options);
s.push_str(&encode_ty(tcx, ty, dict, encode_ty_options));

// Encode the parameter types
let tys = fn_sig.inputs();
if !tys.is_empty() {
for ty in tys {
let ty = transform_ty(tcx, *ty, transform_ty_options);
let ty = transform_ty(tcx, *ty, &[], transform_ty_options);
s.push_str(&encode_ty(tcx, ty, dict, encode_ty_options));
}

Expand Down Expand Up @@ -770,11 +770,12 @@ fn transform_predicates<'tcx>(
fn transform_args<'tcx>(
tcx: TyCtxt<'tcx>,
args: GenericArgsRef<'tcx>,
parents: &[Ty<'tcx>],
options: TransformTyOptions,
) -> GenericArgsRef<'tcx> {
let args = args.iter().map(|arg| match arg.unpack() {
GenericArgKind::Type(ty) if ty.is_c_void(tcx) => Ty::new_unit(tcx).into(),
GenericArgKind::Type(ty) => transform_ty(tcx, ty, options).into(),
GenericArgKind::Type(ty) => transform_ty(tcx, ty, parents, options).into(),
_ => arg,
});
tcx.mk_args_from_iter(args)
Expand All @@ -784,9 +785,12 @@ fn transform_args<'tcx>(
// c_void types into unit types unconditionally, generalizes pointers if
// TransformTyOptions::GENERALIZE_POINTERS option is set, and normalizes integers if
// TransformTyOptions::NORMALIZE_INTEGERS option is set.
fn transform_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, options: TransformTyOptions) -> Ty<'tcx> {
let mut ty = ty;

fn transform_ty<'tcx>(
tcx: TyCtxt<'tcx>,
mut ty: Ty<'tcx>,
parents: &[Ty<'tcx>],
options: TransformTyOptions,
) -> Ty<'tcx> {
match ty.kind() {
ty::Float(..) | ty::Str | ty::Never | ty::Foreign(..) | ty::CoroutineWitness(..) => {}

Expand Down Expand Up @@ -846,17 +850,20 @@ fn transform_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, options: TransformTyOptio
_ if ty.is_unit() => {}

ty::Tuple(tys) => {
ty = Ty::new_tup_from_iter(tcx, tys.iter().map(|ty| transform_ty(tcx, ty, options)));
ty = Ty::new_tup_from_iter(
tcx,
tys.iter().map(|ty| transform_ty(tcx, ty, &parents, options)),
);
}

ty::Array(ty0, len) => {
let len = len.eval_target_usize(tcx, ty::ParamEnv::reveal_all());

ty = Ty::new_array(tcx, transform_ty(tcx, *ty0, options), len);
ty = Ty::new_array(tcx, transform_ty(tcx, *ty0, &parents, options), len);
}

ty::Slice(ty0) => {
ty = Ty::new_slice(tcx, transform_ty(tcx, *ty0, options));
ty = Ty::new_slice(tcx, transform_ty(tcx, *ty0, &parents, options));
}

ty::Adt(adt_def, args) => {
Expand All @@ -865,7 +872,8 @@ fn transform_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, options: TransformTyOptio
} else if options.contains(TransformTyOptions::GENERALIZE_REPR_C) && adt_def.repr().c()
{
ty = Ty::new_adt(tcx, *adt_def, ty::List::empty());
} else if adt_def.repr().transparent() && adt_def.is_struct() {
} else if adt_def.repr().transparent() && adt_def.is_struct() && !parents.contains(&ty)
{
// Don't transform repr(transparent) types with an user-defined CFI encoding to
// preserve the user-defined CFI encoding.
if let Some(_) = tcx.get_attr(adt_def.did(), sym::cfi_encoding) {
Expand All @@ -884,38 +892,48 @@ fn transform_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, options: TransformTyOptio
// 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.
let mut parents = parents.to_vec();
parents.push(ty);
if ty0.is_any_ptr() && ty0.contains(ty) {
ty = transform_ty(
tcx,
ty0,
&parents,
options | TransformTyOptions::GENERALIZE_POINTERS,
);
} else {
ty = transform_ty(tcx, ty0, options);
ty = transform_ty(tcx, ty0, &parents, options);
}
} else {
// Transform repr(transparent) types without non-ZST field into ()
ty = Ty::new_unit(tcx);
}
} else {
ty = Ty::new_adt(tcx, *adt_def, transform_args(tcx, args, options));
ty = Ty::new_adt(tcx, *adt_def, transform_args(tcx, args, &parents, options));
}
}

ty::FnDef(def_id, args) => {
ty = Ty::new_fn_def(tcx, *def_id, transform_args(tcx, args, options));
ty = Ty::new_fn_def(tcx, *def_id, transform_args(tcx, args, &parents, options));
}

ty::Closure(def_id, args) => {
ty = Ty::new_closure(tcx, *def_id, transform_args(tcx, args, options));
ty = Ty::new_closure(tcx, *def_id, transform_args(tcx, args, &parents, options));
}

ty::CoroutineClosure(def_id, args) => {
ty = Ty::new_coroutine_closure(tcx, *def_id, transform_args(tcx, args, options));
ty = Ty::new_coroutine_closure(
tcx,
*def_id,
transform_args(tcx, args, &parents, options),
);
}

ty::Coroutine(def_id, args) => {
ty = Ty::new_coroutine(tcx, *def_id, transform_args(tcx, args, options));
ty = Ty::new_coroutine(tcx, *def_id, transform_args(tcx, args, &parents, options));
}

ty::Ref(region, ty0, ..) => {
Expand All @@ -927,9 +945,9 @@ fn transform_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, options: TransformTyOptio
}
} else {
if ty.is_mutable_ptr() {
ty = Ty::new_mut_ref(tcx, *region, transform_ty(tcx, *ty0, options));
ty = Ty::new_mut_ref(tcx, *region, transform_ty(tcx, *ty0, &parents, options));
} else {
ty = Ty::new_imm_ref(tcx, *region, transform_ty(tcx, *ty0, options));
ty = Ty::new_imm_ref(tcx, *region, transform_ty(tcx, *ty0, &parents, options));
}
}
}
Expand All @@ -943,9 +961,9 @@ fn transform_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, options: TransformTyOptio
}
} else {
if ty.is_mutable_ptr() {
ty = Ty::new_mut_ptr(tcx, transform_ty(tcx, tm.ty, options));
ty = Ty::new_mut_ptr(tcx, transform_ty(tcx, tm.ty, &parents, options));
} else {
ty = Ty::new_imm_ptr(tcx, transform_ty(tcx, tm.ty, options));
ty = Ty::new_imm_ptr(tcx, transform_ty(tcx, tm.ty, &parents, options));
}
}
}
Expand All @@ -958,9 +976,9 @@ fn transform_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, options: TransformTyOptio
.skip_binder()
.inputs()
.iter()
.map(|ty| transform_ty(tcx, *ty, options))
.map(|ty| transform_ty(tcx, *ty, &parents, options))
.collect();
let output = transform_ty(tcx, fn_sig.skip_binder().output(), options);
let output = transform_ty(tcx, fn_sig.skip_binder().output(), &parents, options);
ty = Ty::new_fn_ptr(
tcx,
ty::Binder::bind_with_vars(
Expand Down Expand Up @@ -990,6 +1008,7 @@ fn transform_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, options: TransformTyOptio
ty = transform_ty(
tcx,
tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), ty),
&parents,
options,
);
}
Expand Down Expand Up @@ -1040,15 +1059,15 @@ pub fn typeid_for_fnabi<'tcx>(
// Encode the return type
let transform_ty_options = TransformTyOptions::from_bits(options.bits())
.unwrap_or_else(|| bug!("typeid_for_fnabi: invalid option(s) `{:?}`", options.bits()));
let ty = transform_ty(tcx, fn_abi.ret.layout.ty, transform_ty_options);
let ty = transform_ty(tcx, fn_abi.ret.layout.ty, &[], transform_ty_options);
typeid.push_str(&encode_ty(tcx, ty, &mut dict, encode_ty_options));

// Encode the parameter types
if !fn_abi.c_variadic {
let mut pushed_arg = false;
for arg in fn_abi.args.iter().filter(|arg| arg.mode != PassMode::Ignore) {
pushed_arg = true;
let ty = transform_ty(tcx, arg.layout.ty, transform_ty_options);
let ty = transform_ty(tcx, arg.layout.ty, &[], transform_ty_options);
typeid.push_str(&encode_ty(tcx, ty, &mut dict, encode_ty_options));
}
if !pushed_arg {
Expand All @@ -1061,7 +1080,7 @@ pub fn typeid_for_fnabi<'tcx>(
if fn_abi.args[n].mode == PassMode::Ignore {
continue;
}
let ty = transform_ty(tcx, fn_abi.args[n].layout.ty, transform_ty_options);
let ty = transform_ty(tcx, fn_abi.args[n].layout.ty, &[], transform_ty_options);
typeid.push_str(&encode_ty(tcx, ty, &mut dict, encode_ty_options));
}

Expand Down
31 changes: 31 additions & 0 deletions tests/ui/sanitizer/cfi-self-ref.rs
View file
Original file line number Diff line number Diff line change
@@ -0,0 +1,31 @@
// Check that encoding self-referential types works with #[repr(transparent)]

//@ needs-sanitizer-cfi
//@ compile-flags: --crate-type=bin -Cprefer-dynamic=off -Clto -Zsanitizer=cfi
//@ compile-flags: -C codegen-units=1 -C opt-level=0
//@ build-pass

use std::marker::PhantomData;

struct X<T> {
x: u8,
p: PhantomData<T>,
}

#[repr(transparent)]
struct Y(X<Y>);

trait Fooable {
fn foo(&self, y: Y);
}

struct Bar;

impl Fooable for Bar {
fn foo(&self, _: Y) {}
}

fn main() {
let x = &Bar as &dyn Fooable;
x.foo(Y(X {x: 0, p: PhantomData}));
}

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