[WIP] 4 - Static allocs#159081
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This patch implements Rust's equivalent of Clang's function pointer type discriminator computation used in pointer authentication. Compatibility with Clang is a primary goal. The discriminator produced for a given external "C" function type must match the value computed by Clang so that function pointers can be exchanged safely between Rust and C code while preserving pointer authentication semantics. The implementation mirrors Clang's behavior in `ASTContext::encodeTypeForFunctionPointerAuth`, ensuring that identical C-compatible function types produce identical discriminators. See: <https://clang.llvm.org/doxygen/ASTContext_8cpp.html#abb1375e068e807917527842d05cadea3>.
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kovdan01
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| /// emitted at that offset. | ||
| /// | ||
| /// Offsets are relative to the beginning of the allocation. | ||
| pub(crate) struct FnPtrDiscriminatorAtOffset { |
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What is the established naming convention in rust for such kind of things? Should this be plural (discriminators)? Especially given the fact that we already have collect_fn_ptr_discriminators
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Sure, FnPtrDiscriminatorsAtOffset it is.
| let variant = def.non_enum_variant(); | ||
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| let Some((_, field)) = variant.fields.iter_enumerated().next() else { | ||
| return; |
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Could you please refer me to tests covering these early-return paths (from this case and from the below cases)? The logic by itself looks sound, but it definitely deserves its own test coverage (which I'm not sure I can correctly identify by myself in the new test suite from PR 8)
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Interesting, this is actually redundant. I initially though it would serve for something like:
#[repr(transparent)]
struct Wrapper(extern "C" fn(i32));
impl Sync for Wrapper {}
static T_WRAPPED_FN_PTR: Wrapper = Wrapper(g);in https://github.com/jchlanda/rust/blob/fb279532dbf253c1f78dd02a3268bfdde8d6d7ad/tests/codegen-llvm/pauth/pauth-fn-ptr-type-discrimination-struct-members.rs#L1, but turns out struct arm handles it just fine. Removing.
While at it, I added a test case for Tupel which was missing (T_TUPLE, T_TUPLE_2 and test_8_tuple_members in the same file). Tests added to the 8th PR.
Thanks!
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This patch introduces the following: * Extends `FnAbi` (`callconv`) with a `ptrauth_type_discriminator` field. This field is only used when emitting pointer authentication call bundles. It is stored in `FnAbi` because the call site is not guaranteed to have access to an `Instance`, so the discriminator cannot always be computed on demand. * Adds support for `llvm.ptrauth.resign`. This intrinsic will be used when support for semantic transmute is added. * Performs a minor API redesign as groundwork for allowing call sites to modify schemas in place.
Also remove error messages/tests that used to guarded it.
The codegen now walks the layout of static initializer types to find extern "C" function pointer fields, computes their type discriminators, and applies those discriminators when emitting authenticated function pointer relocations. Also make sure that type discrimination is never applied to init/fini entries.
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The codegen now walks the layout of statically initialized types to find
extern "C"function pointer fields, computes their type discriminators, and applies those discriminators when emitting authenticated function pointer relocations.Also make sure that type discrimination is never applied to init/fini entries.
This is part 4 of a sequence of 8 PRs, that together aim to bring function pointer type discrimination support:
Useful links:
pauthtestintroduction: Introduce aarch64-unknown-linux-pauthtest target #155722