segmentation violation when receiving

[bomm]

I noticed that sometimes the vhduino program reports a problem

2021-03-31 20:01:30 sigHandler: Unhandled signal 11, terminating

I'm using a Raspberry Pi 3B+ with Raspbian 10.9, libpigpio1 1.71-0~rpt1, kernel 5.4.72-v7+ and an RXB6 receiver connected to GPIO 17.

I was able to reproduce the problem when running vhduino in gdb. When I type a command RF receive 17 and step through the program, the signal occurs after stepping over the call to gpioSetAlertFunc() in rfcontrol_command_receive(). Unfortunately I was not able to get a useful stacktrace.

By analyzing the source code I found that rfcontrol_command_receive() calls gpioSetAlertFunc() to set handle_pigpio_interrupt() as a callback function and then calls RFControl::startReceiving which will assign an inner callback function handleInterrupt() to _hw_interruptCallback using hw_attachInterrupt().

If an interrupt occurs between gpioSetAlertFunc() and hw_attachInterrupt(), the function pointer _hw_interruptCallback can be NULL which can result in a segmentation fault when this function pointer is called.

When debugging, the time between gpioSetAlertFunc() and hw_attachInterrupt() is rather long and the problem occurs every time. When running the program in the normal way, the problematic time interval is short, so the problem doesn't seem to occur every time.

I'm preparing a fix.

[mwittig]

I am very sorry for the delay in reply. Currently, the project is lacking maintainers and I have hardly no time due to work and private commitments. I am very grateful for your detailed problem analysis and PR. I'll look into this asap.