[PAC] Encoder and hash (1/8) by jchlanda · Pull Request #159071 · rust-lang/rust

jchlanda · 2026-07-10T11:16:08Z

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:

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

Would it be possible to add unit tests for hash computation like the ones present in llvm source tree at llvm/unittests/Support/SipHashTest.cpp?

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jchlanda · 2026-07-20T11:56:47Z

Would it be possible to add unit tests for hash computation like the ones present in llvm source tree at llvm/unittests/Support/SipHashTest.cpp?

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Done in: 5e05159

rustbot · 2026-07-24T18:07:24Z

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

cc @Noratrieb

…uwer Rollup of 16 pull requests Successful merges: - #159071 ([PAC] Encoder and hash (1/8)) - #161068 (Ensure TLS accesses don't call the global allocator through panic (part 3) ) - #161332 (Some `GlobalCtxt`/`Session` cleanups) - #161344 (Update the `rustc-perf` submodule) - #150931 (rustdoc: Always document `#[repr(transparent)]` if `#[rustc_pub_transparent]` is applied) - #160582 (Add `remove hidden_glob_reexports item breaks downstream` test) - #160876 (remove unwrap from write_mir_fn_graphviz) - #160927 (Enhance EII UI tests) - #161070 (fix arm homogeneous aggregate ABI) - #161236 (Download auto jobs in citool in parallel) - #161254 (Reserve capacity for 3% anon nodes) - #161283 (Tighten the language used for documenting `TargetOptions::llvm_abiname`) - #161291 (Rename `ProjectionPredicate` and `TraitPredicate`) - #161299 (Remove a bunch of unnecessary explicit lifetimes) - #161307 (make ARM maintainers pingable) - #161308 (Add regression test for rustc diagnostic to recognize variables in match guards)

[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)

rust-bors · 2026-08-19T18:39:01Z

💔 Test for b088fd7 failed: CI. Failed job:

auto - dist-x86_64-linux (web logs, enhanced plaintext logs)

JonathanBrouwer · 2026-08-19T19:26:12Z

@bors retry

…=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](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)

…uwer Rollup of 26 pull requests Successful merges: - #161384 (Bust sccache's cache) - #161325 (Bump bootstrap to 1.99.0-beta.1) - #161344 (Update the `rustc-perf` submodule) - #161366 (Subtree sync for rustc_codegen_cranelift) - #159071 ([PAC] Encoder and hash (1/8)) - #160639 ([rustdoc] Only generate search DOM elements if the search is actually needed) - #161068 (Ensure TLS accesses don't call the global allocator through panic (part 3) ) - #161332 (Some `GlobalCtxt`/`Session` cleanups) - #150931 (rustdoc: Always document `#[repr(transparent)]` if `#[rustc_pub_transparent]` is applied) - #158999 (doc: list all remove_dir_all fallback targets) - #160582 (Add `remove hidden_glob_reexports item breaks downstream` test) - #160876 (remove unwrap from write_mir_fn_graphviz) - #160927 (Enhance EII UI tests) - #161070 (fix arm homogeneous aggregate ABI) - #161190 (fix crash in async-drop and async-gen) - #161236 (Download auto jobs in citool in parallel) - #161254 (Reserve capacity for 3% anon nodes) - #161283 (Tighten the language used for documenting `TargetOptions::llvm_abiname`) - #161291 (Rename `ProjectionPredicate` and `TraitPredicate`) - #161293 (add relnotes 1.98.0) - #161299 (Remove a bunch of unnecessary explicit lifetimes) - #161307 (make ARM maintainers pingable) - #161308 (Add regression test for rustc diagnostic to recognize variables in match guards) - #161346 (Don't rely on std traits not being const in tests) - #161360 (vec: fixup the name that i forgot) - #161367 (Reflect current PR title names for subtree syncs in triagebot no-merges)

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)

…uwer Rollup of 26 pull requests Successful merges: - rust-lang/rust#161384 (Bust sccache's cache) - rust-lang/rust#161325 (Bump bootstrap to 1.99.0-beta.1) - rust-lang/rust#161344 (Update the `rustc-perf` submodule) - rust-lang/rust#161366 (Subtree sync for rustc_codegen_cranelift) - rust-lang/rust#159071 ([PAC] Encoder and hash (1/8)) - rust-lang/rust#160639 ([rustdoc] Only generate search DOM elements if the search is actually needed) - rust-lang/rust#161068 (Ensure TLS accesses don't call the global allocator through panic (part 3) ) - rust-lang/rust#161332 (Some `GlobalCtxt`/`Session` cleanups) - rust-lang/rust#150931 (rustdoc: Always document `#[repr(transparent)]` if `#[rustc_pub_transparent]` is applied) - rust-lang/rust#158999 (doc: list all remove_dir_all fallback targets) - rust-lang/rust#160582 (Add `remove hidden_glob_reexports item breaks downstream` test) - rust-lang/rust#160876 (remove unwrap from write_mir_fn_graphviz) - rust-lang/rust#160927 (Enhance EII UI tests) - rust-lang/rust#161070 (fix arm homogeneous aggregate ABI) - rust-lang/rust#161190 (fix crash in async-drop and async-gen) - rust-lang/rust#161236 (Download auto jobs in citool in parallel) - rust-lang/rust#161254 (Reserve capacity for 3% anon nodes) - rust-lang/rust#161283 (Tighten the language used for documenting `TargetOptions::llvm_abiname`) - rust-lang/rust#161291 (Rename `ProjectionPredicate` and `TraitPredicate`) - rust-lang/rust#161293 (add relnotes 1.98.0) - rust-lang/rust#161299 (Remove a bunch of unnecessary explicit lifetimes) - rust-lang/rust#161307 (make ARM maintainers pingable) - rust-lang/rust#161308 (Add regression test for rustc diagnostic to recognize variables in match guards) - rust-lang/rust#161346 (Don't rely on std traits not being const in tests) - rust-lang/rust#161360 (vec: fixup the name that i forgot) - rust-lang/rust#161367 (Reflect current PR title names for subtree syncs in triagebot no-merges)

…=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)

RalfJung · 2026-09-08T10:04:30Z

+    Void,
+}
+
+// Canonicalize Option-wrapped pointer types used to model C nullable pointers.


This is yet another copy of code that already exists multiple times in different forms in the compiler. (And it is wrong for multiple reasons: it does not take into account repr(transparent), and it mixes up raw pointers and references.)

I don't know when we should put our foot down and refuse to add more copies of the same code, insisting on a refactor instead. But I know that if we keep going like this, we'll end up with an unmaintainable buggy mess.

(Also see #119183.)

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jchlanda force-pushed the jakub/pac_ty_disc_PR_1 branch from d798449 to 4c1b0ac Compare July 17, 2026 09:46

kovdan01 reviewed Jul 20, 2026

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jchlanda force-pushed the jakub/pac_ty_disc_PR_1 branch 2 times, most recently from 03337eb to 8b0e0ca Compare July 24, 2026 15:29

jchlanda changed the title ~~[WIP] 1 - Encoder and hash~~ [PAC] Encoder and hash (1/8) Jul 24, 2026

jchlanda marked this pull request as ready for review July 24, 2026 18:07

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 24, 2026

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JonathanBrouwer mentioned this pull request Aug 19, 2026

Rollup of 23 pull requests #161372

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Rollup of 25 pull requests #161383

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Rollup of 26 pull requests #161396

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rust-bors Bot merged commit 9fe1431 into rust-lang:main Aug 20, 2026
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jchlanda mentioned this pull request Sep 2, 2026

[WIP] pac ty disc #158567

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[PAC] Encoder and hash (1/8) - #159071

[PAC] Encoder and hash (1/8)#159071
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