[PAC] FPTR_TYPE_DISCR in ABI Version (3/8) by jchlanda · Pull Request #159075 · rust-lang/rust

jchlanda · 2026-07-10T12:21:05Z

This patch extends the ABI version to include FPTR_TYPE_DISCR. It also removes the diagnostics and tests that previously guarded the unsupported function pointer type discrimination feature, since that functionality is now implemented.

This is part 3 of a sequence of 8 PRs that together implement support for function pointer type discrimination:

4.5 ABI-compatibility

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

kovdan01 · 2026-07-20T08:23:14Z

            | (u32::from(self.indirect_gotos) << GOTOS)
-            | (u32::from(self.typeinfo_vt_ptr_discrimination) << TYPEINFO_VT_PTR_DISCR);
+            | (u32::from(self.typeinfo_vt_ptr_discrimination) << TYPEINFO_VT_PTR_DISCR)
+            | (u32::from(self.function_pointers.as_ref().is_some_and(|schema| {


Would it be beneficial to add some assertion ensuring that if function_pointers is some, it's kind must be only PointerAuthDiscrimination::Type?

View changes since the review

That's not always true though,PointerAuthOption::Calls will result in default function pointer schema, which does not specify PointerAuthDiscrimination::Type (it uses: PointerAuthDiscrimination::None).

See here: https://github.com/jchlanda/rust/blob/951b6709c88f26ff7cf1848a553709478058d971/compiler/rustc_session/src/session.rs#L249

rustbot · 2026-07-24T18:08:06Z

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

cc @Noratrieb

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

Rollup merge of #159071 - jchlanda:jakub/pac_ty_disc_PR_1, r=davidtwco [PAC] Encoder and hash (1/8) This patch implements Rust's equivalent of Clang's function pointer type discriminator computation used for pointer authentication. Compatibility with Clang is a primary design goal. For a given extern "C" function type, the discriminator produced by Rust 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 is part 1 of a sequence of 8 PRs that together implement support for function pointer type discrimination: 1. [Encoder and hash](#159071) 2. [FnAbi, llvm.ptrauth.resign and Session API change](#159074) 3. [FPTR_TYPE_DISCR in ABI Version](#159075) 4. [Static allocs](#159081) 5. [Transmutes](#159082) 6. [Propagate discriminator logic through remaining get_fn_ptr calls sites](#159084) 7. [Minicore updates to support fn ptr type discriminator tests](#159086) 8. [Fn ptr type discrimination tests](#159087) --- Useful links: * Previous PAC work: * `pauthtest` introduction: #155722 * Library support follow up: #156548 * Config follow up: #156712 * [Project goal](https://rust-lang.github.io/rust-project-goals/2026/aarch64_pointer_authentication_pauthtest.html) and [tracking issue](rust-lang/goals#618) * Clang's implementation of [ASTContext::encodeTypeForFunctionPointerAuth](https://clang.llvm.org/doxygen/ASTContext_8cpp.html#abb1375e068e807917527842d05cadea3) * LLVM's [SpiHash](https://github.com/llvm/llvm-project/blob/main/third-party/siphash/include/siphash/SipHash.h)

[PAC] Encoder and hash (1/8) This patch implements Rust's equivalent of Clang's function pointer type discriminator computation used for pointer authentication. Compatibility with Clang is a primary design goal. For a given extern "C" function type, the discriminator produced by Rust 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 is part 1 of a sequence of 8 PRs that together implement support for function pointer type discrimination: 1. [Encoder and hash](rust-lang/rust#159071) 2. [FnAbi, llvm.ptrauth.resign and Session API change](rust-lang/rust#159074) 3. [FPTR_TYPE_DISCR in ABI Version](rust-lang/rust#159075) 4. [Static allocs](rust-lang/rust#159081) 5. [Transmutes](rust-lang/rust#159082) 6. [Propagate discriminator logic through remaining get_fn_ptr calls sites](rust-lang/rust#159084) 7. [Minicore updates to support fn ptr type discriminator tests](rust-lang/rust#159086) 8. [Fn ptr type discrimination tests](rust-lang/rust#159087) --- Useful links: * Previous PAC work: * `pauthtest` introduction: rust-lang/rust#155722 * Library support follow up: rust-lang/rust#156548 * Config follow up: rust-lang/rust#156712 * [Project goal](https://rust-lang.github.io/rust-project-goals/2026/aarch64_pointer_authentication_pauthtest.html) and [tracking issue](rust-lang/goals#618) * Clang's implementation of [ASTContext::encodeTypeForFunctionPointerAuth](https://clang.llvm.org/doxygen/ASTContext_8cpp.html#abb1375e068e807917527842d05cadea3) * LLVM's [SpiHash](https://github.com/llvm/llvm-project/blob/main/third-party/siphash/include/siphash/SipHash.h)

jchlanda · 2026-08-28T13:24:30Z

Friendly ping on this one, the next one in the sequence @davidtwco. Thank you.

…=davidtwco [PAC] FnAbi, llvm.ptrauth.resign and Session API change (2/8) 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. The use of an extended `FnAbi` is dictated by the need to issue a ptrauth bundle for [call-like instructions](https://github.com/rust-lang/rust/blob/main/compiler/rustc_codegen_llvm/src/builder.rs#L1477). At that point, we only have access to the `FnAbi` struct (`Instance` is not guaranteed to be available). Fundamentally, the discriminator originates from the source-level function type. Deriving it at the codegen stage would introduce a layering violation: it would require relying on `FnAbi`'s `ArgAbi` (for both return values and arguments) to preserve source-level type information. This is not a guarantee provided by these abstractions (and in code comments), as `FnAbi` represents a lowered calling convention rather than the original function signature. Computing the discriminator at this stage would therefore create a hard dependency on type information being available where it is not intended to be preserved. Carrying the value explicitly avoids reconstructing source-level information from lowered ABI data and keeps the abstraction boundaries intact. --- This is part 2 of a sequence of 8 PRs that together implement support for function pointer type discrimination: 1. [Encoder and hash](rust-lang#159071) 2. [FnAbi, llvm.ptrauth.resign and Session API change](rust-lang#159074) 3. [FPTR_TYPE_DISCR in ABI Version](rust-lang#159075) 4. [Static allocs](rust-lang#159081) 5. [Transmutes](rust-lang#159082) 6. [Propagate discriminator logic through remaining get_fn_ptr calls sites](rust-lang#159084) 7. [Minicore updates to support fn ptr type discriminator tests](rust-lang#159086) 8. [Fn ptr type discrimination tests](rust-lang#159087) --- Useful links: * Previous PAC work: * `pauthtest` introduction: rust-lang#155722 * Library support follow up: rust-lang#156548 * Config follow up: rust-lang#156712 * [Project goal](https://rust-lang.github.io/rust-project-goals/2026/aarch64_pointer_authentication_pauthtest.html) and [tracking issue](rust-lang/goals#618) * Clang's implementation of [ASTContext::encodeTypeForFunctionPointerAuth](https://clang.llvm.org/doxygen/ASTContext_8cpp.html#abb1375e068e807917527842d05cadea3) * LLVM's [SpiHash](https://github.com/llvm/llvm-project/blob/main/third-party/siphash/include/siphash/SipHash.h)

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 tighten the handling of enums.

Also remove error messages/tests that used to guarded it.

rustbot · 2026-09-24T10:22:08Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

jchlanda force-pushed the jakub/pac_ty_disc_PR_3 branch 2 times, most recently from d746518 to a098946 Compare July 14, 2026 07:27