bjoernager/rust
bjoernager/rust
1
Fork 0
Code Issues Pull requests Activity

Rollup merge of #104110 - krasimirgg:msan-16, r=nagisa

Browse source 
prevent uninitialized access in black_box for zero-sized-types

Don't read the pointer location in black_box for zero sized types, just emit a memory clobber instead. Addresses  https://github.com/rust-lang/rust/issues/103304 when rust is build against LLVM at HEAD.

Zulip thread: https://rust-lang.zulipchat.com/#narrow/stream/187780-t-compiler.2Fwg-llvm/topic/.28with.20llvm.20at.20HEAD.29.3A.20msan.20error.20in.20core.3A.3Ahint.3A.3Ablack_box
This commit is contained in:
Guillaume Gomez 2022-11-12 17:25:00 +01:00 • committed by GitHub
commit 798815aec5
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
2 changed files with 44 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

15
compiler/rustc_codegen_llvm/src/intrinsic.rs
View file

@ -340,17 +340,26 @@ impl<'ll, 'tcx> IntrinsicCallMethods<'tcx> for Builder<'_, 'll, 'tcx> {
sym::black_box => {
args[0].val.store(self, result);
let result_val_span = [result.llval];
// We need to "use" the argument in some way LLVM can't introspect, and on
// targets that support it we can typically leverage inline assembly to do
// this. LLVM's interpretation of inline assembly is that it's, well, a black
// box. This isn't the greatest implementation since it probably deoptimizes
// more than we want, but it's so far good enough.
//
// For zero-sized types, the location pointed to by the result may be
// uninitialized. Do not "use" the result in this case; instead just clobber
// the memory.
let (constraint, inputs): (&str, &[_]) = if result.layout.is_zst() {
("~{memory}", &[])
} else {
("r,~{memory}", &result_val_span)
};
crate::asm::inline_asm_call(
self,
"",
"r,~{memory}",
&[result.llval],
constraint,
inputs,
self.type_void(),
true,
false,