Figure out if portable-atomic and the trap handler can coexist

[MabezDev]

Before we cut a release, and possibly break a bunch of code, we should figure out if these are actually incompatible. It would suck to break the world and then unbreak it in the next release.

[bugadani]

A thing to try might be codegenning for -imac, but I believe that is also something the users will need to do when they update. (And I also think that would make portable-atomic fall back to the trap mechanism, too?)

[jessebraham]

Has there been any progress here? This is definitely a blocker for the next round of releases, IMO, and would be great to resolve. I unfortunately an not too familiar with these bits.

[bugadani]

This PR landed and will be in tomorrow's nightly, which may make some difference.

[MabezDev]

I got tired of waiting for it in nightly and built the compiler myself. I don't think its possible for them to coexist nicely.

I think with rust-lang/rust#114499 merged, we should probably just remove the trap handler entirely (xtensa too). The whole reason for the trap handler was because we couldn't just have load_store atomics without enabled +a extension in LLVM, and in doing that we had to then handle CAS operations. This was 2 years ago, things have moved on and portable-atomic is a really nice drop in replacement (and sometimes improvement!) over core.

I think I will make a PR to tear out the trap handler, and enable portable-atomic by default. The only downside to this of course is that we will be stuck on nightly until 1.76. I'd like to hear some input on how we should handle this.

[bugadani]

(xtensa too)

FYI that will break all heapless 0.7-based code as some stuff there uses compare-and-swap operations but does not polyfill them for Xtensa.

[MabezDev]

I think the simple answer is update to 0.8 heapless :D, but good point, definitely worth noting that.

[jessebraham]

I think I will make a PR to tear out the trap handler, and enable portable-atomic by default. The only downside to this of course is that we will be stuck on nightly until 1.76. I'd like to hear some input on how we should handle this.

Oof, that's not ideal, but given the current situation with atomics it's probably justifiable. I'm not sure how many people, if any, are not using a recent nightly anyway, so perhaps the impact will be minimal.

I'd just say move forward with the PR, if you don't mind, and then we can make a final decision at that point. I'd like to sleep on it for now.

[bjoernQ]

I think the simple answer is update to 0.8 heapless :D, but good point, definitely worth noting that.

I think one of our dependencies (of esp-wifi) where we are currently on heapless-0.7 is embedded-svc. It's already updated but would need a release. Can't think of any other dependency but that doesn't mean there isn't one

[bugadani]

Can't think of any other dependency

smoltcp 0.10 still uses it, along with embedded-nal-async

[MabezDev]

The answer is no, but thats okay. With rust-lang/rust#114499 merged, we can now just rely on portable-atomic and remove the trap handler. We did this in #985.

Closing.