Raw pointer alignment checks in debug

[saethlin]

Proposal

Add a MIR transform which inserts an explicit check that a raw pointer is aligned before it is dereferenced, panicking if it isn't. This transform should only be run when debug assertions are enabled.

I have been slowly working on a draft implementation: rust-lang/rust#98112

See also: rust-lang/rust#54915 rust-lang/rust#51713

Mentors or Reviewers

@oli-obk has lightly committed to reviewing the existing implementation

Process

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

• File an issue describing the proposal.
• A compiler team member or contributor who is knowledgeable in the area can second by writing @rustbot second.
  • Finding a "second" suffices for internal changes. If however, you are proposing a new public-facing feature, such as a -C flag, then full team check-off is required.
  • Compiler team members can initiate a check-off via @rfcbot fcp merge on either the MCP or the PR.
• Once an MCP is seconded, the Final Comment Period begins. If no objections are raised after 10 days, the MCP is considered approved.

You can read more about Major Change Proposals on forge.

Comments

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

[rustbot]

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

cc @rust-lang/compiler @rust-lang/compiler-contributors

[oli-obk]

@rustbot second

[nikomatsakis]

I love this!

[nikomatsakis]

I'm nominated this for discussion in the lang team meeting: these sorts of user-visible changes feel like sometimes we ought to discuss. That said, I personally have long wanted us to make debug builds more effective at detecting UB, and I approve of steps in that direction.

[apiraino]

@rustbot label -final-comment-period +major-change-accepted