[PAC] Fn ptr type discrimination tests (8/8) by jchlanda · Pull Request #159087 · rust-lang/rust

jchlanda · 2026-07-10T14:02:37Z

Adds tests for function pointer type discrimination.

Also updates the main pauthtest document to:

list the new tests;
remove the requirement to patch libc, since those changes have already landed; and
document that cc-rs still requires patching because compiler/rustc_llvm/Cargo.toml pins cc to the older version =1.2.16.

This is part 8 of a sequence of 8 PRs that together implement support for function pointer type discrimination:

Useful links:

Previous PAC work:
- pauthtest introduction: Introduce aarch64-unknown-linux-pauthtest target #155722
- Library support follow up: Library support for aarch64-unknown-linux-pauthtest target #156548
- Config follow up: Pointer authentication config and user facing options #156712
Project goal and tracking issue
Clang's implementation of ASTContext::encodeTypeForFunctionPointerAuth
LLVM's SpiHash

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>.

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.

Implement pointer authentication domain handling for function pointer transmutes. When function pointer type discrimination is enabled, transmuting between function pointer types with different authentication domains now re-signs the pointer using the appropriate discriminator.

…addr` call sites Fill in function pointer type discriminators logic across remaining `get_fn_addr` call sites and explicitly avoid applying it where discrimination is not meaningful. Some uses of `get_fn_addr` are intentionally left unsigned, including the EH personality function, entry wrappers, and compiler-generated Rust ABI shims.

And update to the main pauthtest document: * list new tests * remove the need for patching `libc` as the changes to it already went in. Unfortunately `cc-rs` is held back by `compiler/rustc_llvm/Cargo.toml` which pins to an old version: `cc = "=1.2.16"`

rustbot · 2026-07-24T18:09:18Z

rustc_codegen_gcc is developed in its own repository. If possible, consider making this change to rust-lang/rustc_codegen_gcc instead.

cc @antoyo, @GuillaumeGomez

Some changes occurred in src/doc/rustc/src/platform-support

cc @Noratrieb

rustbot · 2026-07-24T18:09:20Z

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jchlanda · 2026-07-24T18:09:25Z

r? compiler