Uhyve hangs if -v (verbose flag) is not used

[n0toose]

Running Uhyve directly (this does not happen with cargo run) seems to cause the process to hang indefinitely without a (graceful) exit:

$ ./target/debug/uhyve ./data/x86_64/hello_world
frequencies: 1331
CPU frequencies are not all equal

$ ./target/debug/uhyve ./data/x86_64/hello_world --pit --thp --ksm -m 2000MiB
frequencies: 2124
CPU frequencies are not all equal

However, running...

$ ./target/debug/uhyve ./data/x86_64/hello_world -v

$ ./target/debug/uhyve ./data/x86_64/rusty_demo -v

seems to work just fine. Using cargo run also works.

Affects 0222ff7, have not managed to bisect where this has seemingly stopped happening yet. Host OS is Ubuntu 24.04.1 LTS x86_64 with 6.8.0-44-generic.

[n0toose]

(I had set the flag to 1 on a previous operating system, forgot to do so again. I assumed that my environment must've broken things somehow - but not in the way that I expected. Perhaps this could explain why the error wasn't caught earlier.)

Possibly related:

• https://github.com/hermit-os/kernel/blob/e608471f42d7b79f871fbe6d60a8b30e50043aef/src/syscalls/interfaces/uhyve.rs#L161

[n0toose]

If I'm not wrong, gdb/pwndbg "thinks" that a bunch of barrier.wait()'s have piled up and are keeping the program from exiting.

log.txt

A working (borderline nonsensical) theory is that the kernel tries to inform Uhyve that it should shut down, but it doesn't (why?/how? probably wrong), therefore, it halts indefinitely:

https://github.com/hermit-os/kernel/blob/e608471f42d7b79f871fbe6d60a8b30e50043aef/src/syscalls/interfaces/uhyve.rs#L161-L169

Therefore, the Vcpu never halts, the VM never exits, and Uhyve won't get stopped.

uhyve/src/bin/uhyve.rs

Line 291 in 0222ff7

process::exit(run_uhyve())

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This also applies to the WIP v2 version of uhyve-interface.