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Track reason for creating a ReifyShim

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KCFI needs to be able to tell which kind of `ReifyShim` it is examining
in order to decide whether to use a concrete type (`FnPtr` case) or an
abstract case (`Vtable` case). You can *almost* tell this from context,
but there is one case where you can't - if a trait has a method which is
*not* `#[track_caller]`, with an impl that *is* `#[track_caller]`, both
the vtable and a function pointer created from that method will be
`ReifyShim(def_id)`.

Currently, the reason is optional to ensure no additional unique
`ReifyShim`s are added without KCFI on. However, the case in which an
extra `ReifyShim` is created is sufficiently rare that this may be worth
revisiting to reduce complexity.
This commit is contained in:
Matthew Maurer 2024-03-25 19:27:43 +00:00
parent 93c2bace58
commit 6aa89f684e
9 changed files with 60 additions and 19 deletions
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2
compiler/rustc_middle/src/mir/visit.rs
View File

@ -341,7 +341,7 @@ macro_rules! make_mir_visitor {
ty::InstanceDef::Intrinsic(_def_id) |
ty::InstanceDef::VTableShim(_def_id) |
ty::InstanceDef::ReifyShim(_def_id) |
ty::InstanceDef::ReifyShim(_def_id, _) |
ty::InstanceDef::Virtual(_def_id, _) |
ty::InstanceDef::ThreadLocalShim(_def_id) |
ty::InstanceDef::ClosureOnceShim { call_once: _def_id, track_caller: _ } |

48
compiler/rustc_middle/src/ty/instance.rs
View File

@ -31,6 +31,28 @@ pub struct Instance<'tcx> {
pub args: GenericArgsRef<'tcx>,
}
/// Describes why a `ReifyShim` was created. This is needed to distingish a ReifyShim created to
/// adjust for things like `#[track_caller]` in a vtable from a `ReifyShim` created to produce a
/// function pointer from a vtable entry.
/// Currently, this is only used when KCFI is enabled, as only KCFI needs to treat those two
/// `ReifyShim`s differently.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
#[derive(TyEncodable, TyDecodable, HashStable)]
pub enum ReifyReason {
/// The `ReifyShim` was created to produce a function pointer. This happens when:
/// * A vtable entry is directly converted to a function call (e.g. creating a fn ptr from a
/// method on a `dyn` object).
/// * A function with `#[track_caller]` is converted to a function pointer
/// * If KCFI is enabled, creating a function pointer from a method on an object-safe trait.
/// This includes the case of converting `::call`-like methods on closure-likes to function
/// pointers.
FnPtr,
/// This `ReifyShim` was created to populate a vtable. Currently, this happens when a
/// `#[track_caller]` mismatch occurs between the implementation of a method and the method.
/// This includes the case of `::call`-like methods in closure-likes' vtables.
Vtable,
}
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
#[derive(TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable, Lift)]
pub enum InstanceDef<'tcx> {
@ -67,7 +89,13 @@ pub enum InstanceDef<'tcx> {
/// Because this is a required part of the function's ABI but can't be tracked
/// as a property of the function pointer, we use a single "caller location"
/// (the definition of the function itself).
ReifyShim(DefId),
///
/// The second field encodes *why* this shim was created. This allows distinguishing between
/// a `ReifyShim` that appears in a vtable vs one that appears as a function pointer.
///
/// This field will only be populated if we are compiling in a mode that needs these shims
/// to be separable, currently only when KCFI is enabled.
ReifyShim(DefId, Option<ReifyReason>),
/// `<fn() as FnTrait>::call_*` (generated `FnTrait` implementation for `fn()` pointers).
///
@ -194,7 +222,7 @@ impl<'tcx> InstanceDef<'tcx> {
match self {
InstanceDef::Item(def_id)
| InstanceDef::VTableShim(def_id)
| InstanceDef::ReifyShim(def_id)
| InstanceDef::ReifyShim(def_id, _)
| InstanceDef::FnPtrShim(def_id, _)
| InstanceDef::Virtual(def_id, _)
| InstanceDef::Intrinsic(def_id)
@ -354,7 +382,9 @@ fn fmt_instance(
match instance.def {
InstanceDef::Item(_) => Ok(()),
InstanceDef::VTableShim(_) => write!(f, " - shim(vtable)"),
InstanceDef::ReifyShim(_) => write!(f, " - shim(reify)"),
InstanceDef::ReifyShim(_, None) => write!(f, " - shim(reify)"),
InstanceDef::ReifyShim(_, Some(ReifyReason::FnPtr)) => write!(f, " - shim(reify-fnptr)"),
InstanceDef::ReifyShim(_, Some(ReifyReason::Vtable)) => write!(f, " - shim(reify-vtable)"),
InstanceDef::ThreadLocalShim(_) => write!(f, " - shim(tls)"),
InstanceDef::Intrinsic(_) => write!(f, " - intrinsic"),
InstanceDef::Virtual(_, num) => write!(f, " - virtual#{num}"),
@ -476,15 +506,16 @@ impl<'tcx> Instance<'tcx> {
debug!("resolve(def_id={:?}, args={:?})", def_id, args);
// Use either `resolve_closure` or `resolve_for_vtable`
assert!(!tcx.is_closure_like(def_id), "Called `resolve_for_fn_ptr` on closure: {def_id:?}");
let reason = tcx.sess.is_sanitizer_kcfi_enabled().then_some(ReifyReason::FnPtr);
Instance::resolve(tcx, param_env, def_id, args).ok().flatten().map(|mut resolved| {
match resolved.def {
InstanceDef::Item(def) if resolved.def.requires_caller_location(tcx) => {
debug!(" => fn pointer created for function with #[track_caller]");
resolved.def = InstanceDef::ReifyShim(def);
resolved.def = InstanceDef::ReifyShim(def, reason);
}
InstanceDef::Virtual(def_id, _) => {
debug!(" => fn pointer created for virtual call");
resolved.def = InstanceDef::ReifyShim(def_id);
resolved.def = InstanceDef::ReifyShim(def_id, reason);
}
_ => {}
}
@ -508,6 +539,7 @@ impl<'tcx> Instance<'tcx> {
debug!(" => associated item with unsizeable self: Self");
Some(Instance { def: InstanceDef::VTableShim(def_id), args })
} else {
let reason = tcx.sess.is_sanitizer_kcfi_enabled().then_some(ReifyReason::Vtable);
Instance::resolve(tcx, param_env, def_id, args).ok().flatten().map(|mut resolved| {
match resolved.def {
InstanceDef::Item(def) => {
@ -544,18 +576,18 @@ impl<'tcx> Instance<'tcx> {
// Create a shim for the `FnOnce/FnMut/Fn` method we are calling
// - unlike functions, invoking a closure always goes through a
// trait.
resolved = Instance { def: InstanceDef::ReifyShim(def_id), args };
resolved = Instance { def: InstanceDef::ReifyShim(def_id, reason), args };
} else {
debug!(
" => vtable fn pointer created for function with #[track_caller]: {:?}", def
);
resolved.def = InstanceDef::ReifyShim(def);
resolved.def = InstanceDef::ReifyShim(def, reason);
}
}
}
InstanceDef::Virtual(def_id, _) => {
debug!(" => vtable fn pointer created for virtual call");
resolved.def = InstanceDef::ReifyShim(def_id);
resolved.def = InstanceDef::ReifyShim(def_id, reason)
}
_ => {}
}

2
compiler/rustc_middle/src/ty/mod.rs
View File

@ -88,7 +88,7 @@ pub use self::context::{
tls, CtxtInterners, CurrentGcx, DeducedParamAttrs, Feed, FreeRegionInfo, GlobalCtxt, Lift,
TyCtxt, TyCtxtFeed,
};
pub use self::instance::{Instance, InstanceDef, ShortInstance, UnusedGenericParams};
pub use self::instance::{Instance, InstanceDef, ReifyReason, ShortInstance, UnusedGenericParams};
pub use self::list::List;
pub use self::parameterized::ParameterizedOverTcx;
pub use self::predicate::{

1
compiler/rustc_middle/src/ty/structural_impls.rs
View File

@ -449,6 +449,7 @@ TrivialTypeTraversalAndLiftImpls! {
crate::ty::ClosureKind,
crate::ty::ParamConst,
crate::ty::ParamTy,
crate::ty::instance::ReifyReason,
interpret::AllocId,
interpret::CtfeProvenance,
interpret::Scalar,

2
compiler/rustc_mir_transform/src/inline.rs
View File

@ -324,7 +324,7 @@ impl<'tcx> Inliner<'tcx> {
// do not need to catch this here, we can wait until the inliner decides to continue
// inlining a second time.
InstanceDef::VTableShim(_)
| InstanceDef::ReifyShim(_)
| InstanceDef::ReifyShim(..)
| InstanceDef::FnPtrShim(..)
| InstanceDef::ClosureOnceShim { .. }
| InstanceDef::ConstructCoroutineInClosureShim { .. }

2
compiler/rustc_mir_transform/src/inline/cycle.rs
View File

@ -84,7 +84,7 @@ pub(crate) fn mir_callgraph_reachable<'tcx>(
// again, a function item can end up getting inlined. Thus we'll be able to cause
// a cycle that way
InstanceDef::VTableShim(_)
| InstanceDef::ReifyShim(_)
| InstanceDef::ReifyShim(..)
| InstanceDef::FnPtrShim(..)
| InstanceDef::ClosureOnceShim { .. }
| InstanceDef::ConstructCoroutineInClosureShim { .. }

2
compiler/rustc_mir_transform/src/shim.rs
View File

@ -55,7 +55,7 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'
// a virtual call, or a direct call to a function for which
// indirect calls must be codegen'd differently than direct ones
// (such as `#[track_caller]`).
ty::InstanceDef::ReifyShim(def_id) => {
ty::InstanceDef::ReifyShim(def_id, _) => {
build_call_shim(tcx, instance, None, CallKind::Direct(def_id))
}
ty::InstanceDef::ClosureOnceShim { call_once: _, track_caller: _ } => {

12
compiler/rustc_symbol_mangling/src/legacy.rs
View File

@ -2,7 +2,7 @@ use rustc_data_structures::stable_hasher::{Hash64, HashStable, StableHasher};
use rustc_hir::def_id::CrateNum;
use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
use rustc_middle::ty::print::{PrettyPrinter, Print, PrintError, Printer};
use rustc_middle::ty::{self, Instance, Ty, TyCtxt, TypeVisitableExt};
use rustc_middle::ty::{self, Instance, ReifyReason, Ty, TyCtxt, TypeVisitableExt};
use rustc_middle::ty::{GenericArg, GenericArgKind};
use std::fmt::{self, Write};
@ -71,8 +71,14 @@ pub(super) fn mangle<'tcx>(
ty::InstanceDef::VTableShim(..) => {
printer.write_str("{{vtable-shim}}").unwrap();
}
ty::InstanceDef::ReifyShim(..) => {
printer.write_str("{{reify-shim}}").unwrap();
ty::InstanceDef::ReifyShim(_, reason) => {
printer.write_str("{{reify-shim").unwrap();
match reason {
Some(ReifyReason::FnPtr) => printer.write_str("-fnptr").unwrap(),
Some(ReifyReason::Vtable) => printer.write_str("-vtable").unwrap(),
None => (),
}
printer.write_str("}}").unwrap();
}
// FIXME(async_closures): This shouldn't be needed when we fix
// `Instance::ty`/`Instance::def_id`.

8
compiler/rustc_symbol_mangling/src/v0.rs
View File

@ -8,8 +8,8 @@ use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
use rustc_middle::ty::layout::IntegerExt;
use rustc_middle::ty::print::{Print, PrintError, Printer};
use rustc_middle::ty::{
self, EarlyBinder, FloatTy, Instance, IntTy, Ty, TyCtxt, TypeVisitable, TypeVisitableExt,
UintTy,
self, EarlyBinder, FloatTy, Instance, IntTy, ReifyReason, Ty, TyCtxt, TypeVisitable,
TypeVisitableExt, UintTy,
};
use rustc_middle::ty::{GenericArg, GenericArgKind};
use rustc_span::symbol::kw;
@ -44,7 +44,9 @@ pub(super) fn mangle<'tcx>(
let shim_kind = match instance.def {
ty::InstanceDef::ThreadLocalShim(_) => Some("tls"),
ty::InstanceDef::VTableShim(_) => Some("vtable"),
ty::InstanceDef::ReifyShim(_) => Some("reify"),
ty::InstanceDef::ReifyShim(_, None) => Some("reify"),
ty::InstanceDef::ReifyShim(_, Some(ReifyReason::FnPtr)) => Some("reify-fnptr"),
ty::InstanceDef::ReifyShim(_, Some(ReifyReason::Vtable)) => Some("reify-vtable"),
ty::InstanceDef::ConstructCoroutineInClosureShim { .. }
| ty::InstanceDef::CoroutineKindShim { .. } => Some("fn_once"),