Expose `target_abi = "pauthtest"`

[jchlanda]

Proposal

I propose adding Pauthtest = "pauthtest" as a possible value of CfgAbi, exposing cfg(target_abi = "pauthtest") for the AArch64 Linux pauthtest target. This makes pauthtest a distinct ABI configuration within rustc rather than merely another name for the default AArch64 ABI.

This MCP is being filed retroactively (apologies), following review feedback on the PR that introduced the target. The PR also added the corresponding LlvmAbi::Pauthtest value.

The target adds support for pointer authentication on AArch64 Linux ELF systems using a musl-based C standard library, using LLVM's aarch64-unknown-linux-pauthtest target triple.

The proposed pauthtest value is useful for gating target-specific pointer-authentication behavior based on the ABI. For example, the pointer authentication implementation uses the ABI to gate code responsible for creating signing schemas. The new ABI value also couples the Rust-visible ABI with the corresponding LLVM ABI, as enforced by the consistency checks.

The name pauthtest is consistent with LLVM's existing terminology.

Mentors or Reviewers

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Process

The main points of the Major Change Process are as follows:

• File an issue describing the proposal.
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• Once an MCP is seconded, the Final Comment Period begins.
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  • Outstanding concerns will block the Final Comment Period from finishing. Once all concerns are resolved, the 10 day countdown is restarted.
  • If no concerns are raised after 10 days since the resolution of the last outstanding concern, the MCP is considered approved.

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[rustbot]

Important

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cc @rust-lang/compiler

[jchlanda]

cc @RalfJung

[RalfJung]

Sorry, there was some confusion here. LlvmAbi is an internal value in rustc, doesn't need an MCP.
But that PR also added a new value for target_abi / target_env, right? That is user-visible and is something we've usually done MCPs for.

EDIT: Yeah, it's the cfg_abi: CfgAbi::Pauthtest I was talking about re: MCP. Not the llvm_abiname: LlvmAbi::Pauthtest. Please update the MCP above.

[jchlanda]

Sorry, there was some confusion here. LlvmAbi is an internal value in rustc, doesn't need an MCP. But that PR also added a new value for target_abi / target_env, right? That is user-visible and is something we've usually done MCPs for.

EDIT: Yeah, it's the cfg_abi: CfgAbi::Pauthtest I was talking about re: MCP. Not the llvm_abiname: LlvmAbi::Pauthtest. Please update the MCP above.

Done, apologies for the confusion.