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[PAC] FPTR_TYPE_DISCR in ABI Version (3/8)#159075

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[PAC] FPTR_TYPE_DISCR in ABI Version (3/8)#159075
jchlanda wants to merge 4 commits into
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jchlanda:jakub/pac_ty_disc_PR_3

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@jchlanda jchlanda commented Jul 10, 2026 •
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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:

  1. Encoder and hash
  2. FnAbi, llvm.ptrauth.resign and Session API change
  3. FPTR_TYPE_DISCR in ABI Version
  4. Static allocs
  5. Transmutes
  6. Propagate discriminator logic through remaining get_fn_ptr calls sites
  7. Minicore updates to support fn ptr type discriminator tests
  8. Fn ptr type discrimination tests

Useful links:

@rustbot rustbot added A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jul 10, 2026
This was referenced Jul 10, 2026
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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
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jchlanda force-pushed the jakub/pac_ty_disc_PR_3 branch from a098946 to e1b80e7 Compare July 14, 2026 08:51
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jchlanda force-pushed the jakub/pac_ty_disc_PR_3 branch from e1b80e7 to 7135bea Compare July 17, 2026 07:03
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jchlanda force-pushed the jakub/pac_ty_disc_PR_3 branch 2 times, most recently from 66aaf1e to 951b670 Compare July 17, 2026 09:47
kovdan01
kovdan01 reviewed Jul 20, 2026
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Comment thread compiler/rustc_session/src/session.rs
| (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| {

@kovdan01 kovdan01 Jul 20, 2026 •
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Would it be beneficial to add some assertion ensuring that if function_pointers is some, it's kind must be only PointerAuthDiscrimination::Type?

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@jchlanda jchlanda Jul 20, 2026

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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

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jchlanda force-pushed the jakub/pac_ty_disc_PR_3 branch from 951b670 to df46abe Compare July 20, 2026 12:52
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jchlanda force-pushed the jakub/pac_ty_disc_PR_3 branch from df46abe to 8c3ef4c Compare July 20, 2026 15:19
jchlanda added 3 commits July 24, 2026 15:24
@jchlanda
[PAC] Introduce function pointer type encoder and hashing function
63b81b4 
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>.
@jchlanda
[PAC] Add unit tests for sip hash
8b0e0ca
@jchlanda
[PAC] Include discriminator in FnAbi, add llvm.ptrauth.resign
69e4d08 
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.
@jchlanda
jchlanda force-pushed the jakub/pac_ty_disc_PR_3 branch from 8c3ef4c to af72799 Compare July 24, 2026 15:37
@jchlanda
[PAC] Enable support for FPTR_TYPE_DISCR in ABI Version
06c9628 
Also remove error messages/tests that used to guarded it.
@jchlanda
jchlanda force-pushed the jakub/pac_ty_disc_PR_3 branch from af72799 to 06c9628 Compare July 24, 2026 15:41
@jchlanda jchlanda changed the title [WIP] 3 - FPTR_TYPE_DISCR in ABI Version [PAC] FPTR_TYPE_DISCR in ABI Version (3/8) Jul 24, 2026
@jchlanda
jchlanda marked this pull request as ready for review July 24, 2026 18:08
@rustbot

rustbot commented Jul 24, 2026

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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

@rustbot 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
@jchlanda

jchlanda commented Jul 24, 2026

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r? compiler

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rustbot commented Jul 24, 2026

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r? @petrochenkov

rustbot has assigned @petrochenkov.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

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@rustbot rustbot assigned nnethercote and unassigned petrochenkov Jul 24, 2026
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nnethercote commented Jul 24, 2026

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rustbot has assigned @petrochenkov

followed immediately by:

@rustbot rustbot assigned nnethercote and unassigned petrochenkov

which is weird.

Anyway, I don't know the first thing about this stuff, so I'll try to find a better reviewer.

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