hiffy unable to call SpRot functions after 46fec52176e26964b65d5ddd5b4e74222de0bd02

[flihp]

I tripped over this after updating an old hubris build and attempting to talk to the SpRot task on my gimletlet. Using the latest humility & hubris from before the subject commit (d4aba7b) we're able to make SpRot calls as expected:

$ humility --target gimletlet hiffy --call=SpRot.status
humility: attached to 0483:374e:000E00103156501920323443 via ST-Link V3
SpRot.status() => SprotStatus { rot: RotStatus { version: Version(0x4), min_version: Version(0x2), request_buf_size: 0x400, response_buf_size: 0x400 }, sp: SpStatus { version: Version(0x4), min_version: Version(0x2), request_buf_size: 0x400, response_buf_size: 0x400 } }

When built from a later commit (the subject commit or later) this now fails:

$ humility --target gimletlet hiffy --call=SpRot.status
humility: attached to 0483:374e:000E00103156501920323443 via ST-Link V3
humility hiffy failed: failed to find SpRot_status_ARGS

Oddly enough the SpRot methods appear to be the only ones affected: Methods like Update.block_size and Hash.init_sha256 still work as expected.

Since the commit in question changes the idolatry built I thought that some code may be missing from the output generated by build.rs. The server_stub.rs generated by stm32h7-sprot-server crate however appears to have the expected SpRot_status_ARGS structure so that may be a dead end.

[hawkw]

Huh, it's pretty weird that this only effects the SpRot API... I'll poke around a bit.

[flihp]

Thanks! 💯 this is weird, especially that it only effects the SpRot. Thanks for taking a look.

[cbiffle]

Alright, this is an interaction of two things, both of which I've got PRs outstanding to fix.

First, Idolatry changed code generation very slightly in a way that caused rustc to stop emitting DWARF for zero-sized ARGS structs, particularly for Hubpack-encoded operations. When I say codegen was changed slightly, I mean replacing let _args = with let _ =. I've fixed this.

However, these args structs are still for all intents and purposes totally unused and zero size, which means I consider rustc at liberty to not emit DWARF for them at any point in the future. I've got a PR outstanding to cause Humility to treat a missing Idol args struct as zero-length. If it ever gets that assumption wrong, the IPC will just cause hiffy to be killed, which we'll notice.

[cbiffle]

As of a couple of minutes ago, Humility 0.11.6 should be able to talk to sprot in this firmware again.

[cbiffle]

Hubris has been revved to include the fixes in the Idol compiler. Firmware built after ~today should be compatible with earlier versions of Humility; versions of Humility after ~today should be compatible with all versions of the firmware.