[WIP] pac ty disc by jchlanda · Pull Request #158567 · rust-lang/rust

jchlanda · 2026-06-29T15:17:00Z

bjorn3 · 2026-06-29T15:35:55Z

+        cv: Scalar,
+        layout: abi::Scalar,
+        llty: Self::Type,
+        schema: Option<PointerAuthSchema>,


This function should have access to the Session already through self.tcx.sess.

View changes since the review

bjorn3 · 2026-06-29T15:36:05Z

+    fn get_fn_addr(
+        &self,
+        instance: Instance<'tcx>,
+        pointer_auth_schema: Option<PointerAuthSchema>,


Same

View changes since the review

kovdan01 · 2026-07-01T15:40:45Z

+        _new_key: u32,
+        _new_discriminator: u64,
+    ) -> Self::Value {
+        bug!("Resigning of pointers not implemented");


Is there a test for this (ensuring that it's not supported) or is it infeasible to reach this path?

View changes since the review

It is not a user facing function, so the only way it could be triggered is if we wrote incorrect code within the compiler itself, hence the bug!. The relevant call chain for this function starts inside codegen_transmute and is guarded by a function pointer support check.

kovdan01 · 2026-07-01T15:43:38Z

+    // Direct function pointer.
+    if let Some(input) = build_fn_ptr_type_discriminator_input(tcx, ty) {
+        // Only support about extern "C".
+        if matches!(input.abi(), ExternAbi::C { .. } | ExternAbi::System { .. }) {


Could you please explain what ExternAbi::System stands for? I would appreciate if you also refer me to the corresponding test

View changes since the review

System means the platform’s default system ABI for foreign functions, whatever the platform uses by default for system libraries. I was told in one of the PRs that for all practical cases they should match. Hence the inclusion of both.

The docs.

kovdan01 · 2026-07-01T15:46:14Z


        let address_space = cx.tcx.global_alloc(prov.alloc_id()).address_space(cx);
-        let schema = if cx.sess().pointer_authentication() {
+        let mut schema = if cx.sess().pointer_authentication() {


Why do we need mut here?

View changes since the review

Because we then retrieve the discriminator and store it in the schema.

kovdan01 · 2026-07-01T15:48:29Z

        operand: OperandRef<'tcx, Bx::Value>,
        cast: TyAndLayout<'tcx>,
    ) -> OperandValue<Bx::Value> {
+        debug!(


Is this intended to be included in the PR or is it a development-stage-only debug printing?

View changes since the review

Intended. This serves the same purpose as LLVM_DEBUG(dbgs()...) in llvm.

kovdan01 · 2026-07-01T15:49:59Z

 pub mod middle;
 pub mod mir;
 pub mod mono;
+pub mod ptrauth;


There are no other changes in the file - so, is this actually needed?

View changes since the review

Yes.
This says something along the lines of: "There is a module called ptrauth, and it should be included in the library’s public interface.If you go toptrauthdirectory you'll see themod.rs` which in turns tells us what is publicly exported from the module.
So the flow of visibility is: lib.rs -> ptrauth -> discriminator / llvm_siphash (where the last two are controlled by https://github.com/jchlanda/rust/blob/9545275cededc9e307c61ef9d640d256ae59eab3/compiler/rustc_middle/src/ptrauth/mod.rs#L5)

kovdan01 · 2026-07-01T22:09:27Z

This deleted test should also be removed from the markdown documentation file which includes it in test coverage

View changes since the review

Yeap, need to work on that file a bit more.

kovdan01 · 2026-07-01T22:27:56Z

    pub c_variadic: bool,
+
+    /// Computed type discriminator for pointer authentication purpose.
+    pub type_discriminator: u64,


It's probably worth prefixing ptrauth-related things with smth like ptrauth_ in such "generic" places (which are not ptrauth-specific). A comment here contains explanation, but when constructing struct objects we have type_discriminator: XXX which non-ptrauth-aware reader would not easily understand

View changes since the review

OK, renamed to ptrauth_type_discriminator.

kovdan01 · 2026-07-01T22:30:03Z

            fixed_count: self.fixed_count,
            conv: self.conv.stable(tables, cx),
            c_variadic: self.c_variadic,
+            type_discriminator: 0,


Could you please explain why we have 0 here and are there any cases when non-zero discriminator would be needed here?

View changes since the review

I think you are on to something. There are 3 structs with the same name (FnAbi): public, callconv and gcc. I wonder if we could get away with only extending callconv.

I'll get back to you on this one.

Yeap, the only one we need is the callconv, refactored.

kovdan01 · 2026-07-01T22:31:59Z

            fixed_count: 3,
            conv: CanonAbi::C,
            can_unwind: false,
+            type_discriminator: 0,


Probably deserves a comment that it's just a placeholder value since gcc backend is not supported for pointer authentication (if I got your reasoning right)

View changes since the review

Same as above.

kovdan01 · 2026-07-01T22:40:30Z

+            fn_ptr_discriminators.as_ref().and_then(|m| m.get(Size::from_bytes(offset as u64)));
+
+        if let (Some(schema), Some(discr)) = (schema.as_mut(), discr) {
+            schema.constant_discriminator = discr as u16;


Does this override discriminator value for init/fini if fn ptr type discr is enabled? If so, it looks diverging from how clang handles this - and my understanding is that it actually makes sense to have hard-coded separate discriminator for init/fini since these are (a) known type (b) we need to know discriminator in dynamic loader.

View changes since the review

Are you saying that discriminator for init/fini must always be 0xd9d4, regardless if fn ptr type discrimination is on or not? If so, than we've got a bug, as it would be indeed overridden. Let me see what clang does and come back to you.

Right, we do have a bug. Clang does:

no init/fini, no fn ptr ty disc:

@llvm.global_ctors = appending global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 90, ptr @foo, ptr null }]

init/fini, no fn ptr ty disc:

@llvm.global_ctors = appending global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 90, ptr ptrauth (ptr @foo, i32 0, i64 55764, ptr inttoptr (i64 1 to ptr)), ptr null }]

no init/fini, fn ptr ty disc:

@llvm.global_ctors = appending global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 90, ptr @foo, ptr null }]

init/fini, fn ptr ty disc:

@llvm.global_ctors = appending global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 90, ptr ptrauth (ptr @foo, i32 0, i64 55764, ptr inttoptr (i64 1 to ptr)), ptr null }]

I'll have to fix that in rust.

OK, fixed now, extended the test with O{0|3}_PAUTH-INIT-FINI-FN-TY-DISC.

This patch brings: * unified handling of pointer authentication options through: `-Zpointer-authentication`, with possible values: `aarch64-jump-table-hardening`, `auth-traps`, `calls`, `elf-got`, `function-pointer-type-discrimination`, `indirect-gotos`, `init-fini`, `init-fini-address-discrimination`, `return-addresses`. Toggled with `+`/`-`. * centralized handling of pointer authentication features. Session holds `pointer_auth_config: Option<PointerAuthConfig>` * encapsulation of schema for function pointers and init/fini through `PointerAuthSchema`. This allowed for retiring of `PacMetadata`. * refactor enabling of pointer authentication in code, instead of relying on the target (`pauthtest`) use the session

- warning on unsupported test - error on type discrimination - removal of PointerAuthKind

Also improve the API design of pointer_authentication_functions, by making it return Option<&PointerAuthSchema>, rather than bool.

Alongside Rust implementation of LLVM's SipHash-2-4.

This is only to be used when emitting an operand bundle, which might not have access to an Instance of the function, but for which FnAbi is guaranteed to be correct.

Start moving away from global schema, by cloning it into users. Helpers for fn ptr type discrimination status and value of the key.

This is a move away from a blind bitcast between the types. Now, when dealing with function pointers, transmute will detect a domain change (change of fn ptr type) and issue resigning.

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bjorn3 reviewed Jun 29, 2026

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jchlanda added 3 commits June 30, 2026 11:28

Add library support for aarch64-unknown-linux-pauthtest

f89e171

Use target_env = "musl" & target_abi = "pauthtest" instead of env

1098014

Update landing pad to use addr()

f971add

jchlanda force-pushed the jakub/pac_ty_disc branch from 2d3b257 to f5fa52a Compare June 30, 2026 11:57

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jchlanda force-pushed the jakub/pac_ty_disc branch from d6ce62a to 755b0b7 Compare June 30, 2026 15:08

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jchlanda force-pushed the jakub/pac_ty_disc branch from 755b0b7 to c3fd17f Compare June 30, 2026 15:23

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jchlanda force-pushed the jakub/pac_ty_disc branch from c3fd17f to 8b6e351 Compare July 1, 2026 06:23

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jchlanda force-pushed the jakub/pac_ty_disc branch from 8b6e351 to 5b8ba19 Compare July 1, 2026 07:24

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jchlanda force-pushed the jakub/pac_ty_disc branch from 5b8ba19 to 9545275 Compare July 1, 2026 08:41

jchlanda added 2 commits July 1, 2026 09:15

PR feedback: Add library support

f16c778

PR feedback: Use target_env

0f43920

jchlanda force-pushed the jakub/pac_ty_disc branch from 4301abb to 9545275 Compare July 1, 2026 15:06

kovdan01 reviewed Jul 1, 2026

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jchlanda mentioned this pull request Jul 2, 2026

Pointer authentication config and user facing options #156712

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jchlanda force-pushed the jakub/pac_ty_disc branch from 3a40e3c to 697c5ce Compare July 2, 2026 14:55

jchlanda added 7 commits July 3, 2026 10:35

Use rust_force_inline on sign_lpad function

4c59d2c

Extend version support with C++ specifics

7ce1389

Document -Zpointer-authentication option

e3b1a62

PR feedback

e0da319

- warning on unsupported test - error on type discrimination - removal of PointerAuthKind

PR feedback

16d4efe

Convert -Zpointer-authentication to target modifier

1c82b8f

Also improve the API design of pointer_authentication_functions, by making it return Option<&PointerAuthSchema>, rather than bool.

jchlanda force-pushed the jakub/pac_ty_disc branch from 697c5ce to eef2752 Compare July 3, 2026 14:44

jchlanda added 10 commits July 3, 2026 14:44

Teach builder how to issue llvm.ptrauth.resign

704698c

Introduce function pointer type encoder

5548abc

Alongside Rust implementation of LLVM's SipHash-2-4.

Extend FnAbi to hold type_discriminator

00fd69a

This is only to be used when emitting an operand bundle, which might not have access to an Instance of the function, but for which FnAbi is guaranteed to be correct.

Add FPTR_TYPE_DISCR to the supported set of features

08fd0a0

Start moving away from global schema, by cloning it into users. Helpers for fn ptr type discrimination status and value of the key.

Teach static initializer how to handle fn ptr discriminators

7a3678f

Extend transmute to handle fn ptr discriminators

ddba18c

This is a move away from a blind bitcast between the types. Now, when dealing with function pointers, transmute will detect a domain change (change of fn ptr type) and issue resigning.

Extend minicore with items required by fn ptr ty discriminator tests

cb7bee5

Add fn ptr type discrimination tests

81c37ba

Update SIMD vector encoding and extend the testing for it

7109ee6

PR feedback: FnAbi

96d5f58

jchlanda force-pushed the jakub/pac_ty_disc branch from eef2752 to 96d5f58 Compare July 3, 2026 14:45

Init/fini entries don't participate in fn ty discrimination

3fe0e17

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