Oh where oh where can my arg5 be?

Start by reproducing the issue on an M1 macOS system with the port-process-return DTrace probe, then run the OPTE tests using cargo test --features usdt from the opte checkout. The work is done when a probe with six arguments reports the value passed in the arg5 position instead of NULL.

As I mentioned in #61, I'm seeing some issues around usdt while working on oxidecomputer/opte#145. I'm going to eschew the background and get straight to it.

Issue

EDIT: This is an M1 (ARM) mac.

On macOS I cannot seem to pass more than five arguments to a probe. As part of my change to OPTE (in the above link) I added an epoch argument to the port__process__return probe, now giving it a total of six arguments, pushing the res argument to arg5 position. After doing this the probe always fires with an arg5 of NULL.

$ sudo dtrace -Zn 'port-process-return { trace(arg5); }'
Password:
dtrace: description 'port-process-return ' matched 0 probes
CPU     ID                    FUNCTION:NAME
  5  14747 _ZN4opte6engine4port4Port25port_process_return_probe17hec39bcf71fd676a8E:port-process-return                 0
  2  14747 _ZN4opte6engine4port4Port25port_process_return_probe17hec39bcf71fd676a8E:port-process-return                 0
  4  14747 _ZN4opte6engine4port4Port25port_process_return_probe17hec39bcf71fd676a8E:port-process-return                 0
  9  14747 _ZN4opte6engine4port4Port25port_process_return_probe17hec39bcf71fd676a8E:port-process-return                 0
  6  14747 _ZN4opte6engine4port4Port25port_process_return_probe17hec39bcf71fd676a8E:port-process-return                 0
  7  14747 _ZN4opte6engine4port4Port25port_process_return_probe17hec39bcf71fd676a8E:port-process-return                 0
  8  14747 _ZN4opte6engine4port4Port25port_process_return_probe17hec39bcf71fd676a8E:port-process-return                 0
  8  14747 _ZN4opte6engine4port4Port25port_process_return_probe17hec39bcf71fd676a8E:port-process-return                 0
  7  14747 _ZN4opte6engine4port4Port25port_process_return_probe17hec39bcf71fd676a8E:port-process-return                 0
  8  14747 _ZN4opte6engine4port4Port25port_process_return_probe17hec39bcf71fd676a8E:port-process-return                 0
  8  14747 _ZN4opte6engine4port4Port25port_process_return_probe17hec39bcf71fd676a8E:port-process-return                 0
  6  14747 _ZN4opte6engine4port4Port25port_process_return_probe17hec39bcf71fd676a8E:port-process-return                 0
  6  14747 _ZN4opte6engine4port4Port25port_process_return_probe17hec39bcf71fd676a8E:port-process-return                 0

Reproduce

1. Clone the opte repo onto a macOS box and checkout the opte-143-set-fw-rules branch.
2. In one window trace arg5 of the port-process-return probe.

$ sudo dtrace -Zn 'port-process-return { trace(arg5); }'

3. In another window run the OPTE unit tests with the usdt feature.

$ cd opte
$ cargo test --features usdt