bjoernager/rust
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Auto merge of #99420 - RalfJung:vtable, r=oli-obk

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make vtable pointers entirely opaque

This implements the scheme discussed in https://github.com/rust-lang/unsafe-code-guidelines/issues/338: vtable pointers should be considered entirely opaque and not even readable by Rust code, similar to function pointers.

- We have a new kind of `GlobalAlloc` that symbolically refers to a vtable.
- Miri uses that kind of allocation when generating a vtable.
- The codegen backends, upon encountering such an allocation, call `vtable_allocation` to obtain an actually dataful allocation for this vtable.
- We need new intrinsics to obtain the size and align from a vtable (for some `ptr::metadata` APIs), since direct accesses are UB now.

I had to touch quite a bit of code that I am not very familiar with, so some of this might not make much sense...
r? `@oli-obk`
This commit is contained in:
bors 2022-07-22 01:33:49 +00:00
commit aa01891700
69 changed files with 673 additions and 527 deletions
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2
compiler/rustc_mir_transform/src/inline.rs
View file

@ -246,7 +246,7 @@ impl<'tcx> Inliner<'tcx> {
// not get any optimizations run on it. Any subsequent inlining may cause cycles, but we
// do not need to catch this here, we can wait until the inliner decides to continue
// inlining a second time.
InstanceDef::VtableShim(_)
InstanceDef::VTableShim(_)
| InstanceDef::ReifyShim(_)
| InstanceDef::FnPtrShim(..)
| InstanceDef::ClosureOnceShim { .. }

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

@ -79,7 +79,7 @@ pub(crate) fn mir_callgraph_reachable<'tcx>(
// These have MIR and if that MIR is inlined, substituted and then inlining is run
// again, a function item can end up getting inlined. Thus we'll be able to cause
// a cycle that way
InstanceDef::VtableShim(_)
InstanceDef::VTableShim(_)
| InstanceDef::ReifyShim(_)
| InstanceDef::FnPtrShim(..)
| InstanceDef::ClosureOnceShim { .. }

6
compiler/rustc_mir_transform/src/shim.rs
View file

@ -32,7 +32,7 @@ fn make_shim<'tcx>(tcx: TyCtxt<'tcx>, instance: ty::InstanceDef<'tcx>) -> Body<'
let mut result = match instance {
ty::InstanceDef::Item(..) => bug!("item {:?} passed to make_shim", instance),
ty::InstanceDef::VtableShim(def_id) => {
ty::InstanceDef::VTableShim(def_id) => {
build_call_shim(tcx, instance, Some(Adjustment::Deref), CallKind::Direct(def_id))
}
ty::InstanceDef::FnPtrShim(def_id, ty) => {
@ -113,7 +113,7 @@ enum Adjustment {
/// We get passed `&[mut] self` and call the target with `*self`.
///
/// This either copies `self` (if `Self: Copy`, eg. for function items), or moves out of it
/// (for `VtableShim`, which effectively is passed `&own Self`).
/// (for `VTableShim`, which effectively is passed `&own Self`).
Deref,
/// We get passed `self: Self` and call the target with `&mut self`.
@ -569,7 +569,7 @@ fn build_call_shim<'tcx>(
// FIXME(eddyb) avoid having this snippet both here and in
// `Instance::fn_sig` (introduce `InstanceDef::fn_sig`?).
if let ty::InstanceDef::VtableShim(..) = instance {
if let ty::InstanceDef::VTableShim(..) = instance {
// Modify fn(self, ...) to fn(self: *mut Self, ...)
let mut inputs_and_output = sig.inputs_and_output.to_vec();
let self_arg = &mut inputs_and_output[0];