Segfault on context creation

[Brandon Dube]

A MWE:

package main

import (
	"log"

	"github.com/gotmc/usbtmc"
	_ "github.com/gotmc/usbtmc/driver/truveris"
)

func main() {
	ctx, err := usbtmc.NewContext()
	if err != nil {
		log.Fatal(err)
	}
	ctx.SetDebugLevel(1)
}

Output:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x49c9c0]

goroutine 1 [running]:
<>/vendor/github.com/gotmc/usbtmc.NewContext(0x4c92e0, 0x78a790, 0x0)
	/media/psf/Home/go/src/<>/vendor/github.com/gotmc/usbtmc/context.go:20 +0x70
main.main()
	/media/psf/Home/go/src/<>/cmd/ldctest/main.go:19 +0x26

This is without any of the other drivers installed. If I uninstall this driver and install another, I get the same segfault with the other two.

[Matthew Rankin]

@brandondube

1. Do you have the libusb driver installed (e.g., brew install libusb on macOS)?
2. Did you run your Go program with root privileges (e.g., sudo myprog)?

[Brandon Dube]

Libusb1.0-dev is installed (and the lib is on the path), I didn’t run with sudo but lsusb-vvv doesn’t complain about permissions / cant open devices.

‘Bare’ google/gousb context succeeded but usbtmc panics.

[Matthew Rankin]

Have you tried running as sudo?

[Matthew Rankin]

@brandondube — A few more questions:

1. What test equipment are you trying to communicate with?
2. What hardware and O/S are you using?
3. What version of libusb are you using?

[Matthew Rankin]

I just noticed that there had been a typo in the README if you were trying to use the google/gousb driver. The correct import statement should be:

import (
	"github.com/gotmc/usbtmc"
	_ "github.com/gotmc/usbtmc/driver/google"
)

Prior to running that, make sure you install the google/gousb driver using

$ go get -v github.com/google/gousb

[Brandon Dube]

The typo is probably the cause. I'm not back at work until the week after next, but to the 1,2,3 above:

1. test equipment - Thorlabs ITC4001

2. hardware / OS -- a supermicro server (or at least one in a supermicro case, not sure who the mfg is) in a standard ATX chassis, USB 2.0 connection over the Thorlabs provided cable. Ubuntu 16.04 LTS.

3. libusb-dev 1.0.12

I did not try sudo, my user account on the server has permissions to access USB devices, but I don't have (and definitely can't get) sudo -- our IT manages that.

If it is the typo, checking if the driver is nil before the first call that uses it and bailing then would be a sensible fix. Perhaps the valid/usable import statements (_ "...") could be included in a fmt.Errorf.

In the interim, I have already made a very bare-bones impl of usbtmc for that thorlabs controller on top of google/gousb with hardcoded vid/pid, endpoint nos, etc, and bulk transfer r/w only, though it is owned by my employer so I cannot share.

[Matthew Rankin]

Closing due to inactivity. Let me know if this is still an issue, and I'll reopen.