Design meeting: resolve ABI issues around target-feature

[RalfJung]

Summary

Target features generally control which instructions codegen may use during the final step of generating assembly, but some of them also affect how arguments and return values are passed across function call boundaries.
This means that in general, code compiled with different target features is not ABI-compatible and cannot be linked with each other.
In particular, since the standard library is shipped in binary form pre-built for the default set of target features, enabling/disabling particular features means that calling standard library methods suddenly causes Undefined Behavior.
That's a soundness bug that we clearly should tackle.

Background reading

Design meeting document: https://hackmd.io/e4bYAMh2RWG2yKZHivmF9Q

• Tracking issue: 32bit x86 targets without SSE2 have unsound floating point behavior rust#114479
• The ABI of float types can be changed by -Ctarget-feature rust#116344
• Remove ability to disable some target features rust#116584

About this issue

This issue corresponds to a lang-team design meeting proposal. It corresponds to a possible topic of discussion that may be scheduled for deeper discussion during one of our design meetings.

[calebzulawski]

I don't know the intended permissions, but the hackmd isn't publicly visible

[RalfJung]

Sorry for that -- fixed.

[RalfJung]

@traviscross

This question is scheduled for a T-lang design meeting on 2023-12-20

With the rust-lang website down... can you remind us of the time and place of these meetings?

[RalfJung]

I did find the calendar link on this page but I can't view the calendar, it requires logging with a Google account and I don't have one (nor do I want to create one).

[Jules-Bertholet]

1pm - 2pm (Eastern Time - New York)
Wed Dec 20, 2023
https://meet.jit.si/ferris-rules
Design meeting schedule: T-lang design meeting schedule