Re: Segmentation fault when using asyn Octect writeRead

[Mark Rivers via Tech-talk <tech-talk at aps.anl.gov>]

Hi Abdalla,

I think I see an error in your driver:

    memcpy(tx_array + 0, &(tx.status),  sizeof(u16));

    memcpy(tx_array + 2, &(tx.command), sizeof(u16));

    memcpy(tx_array + 2, &(tx.address), sizeof(u16));

    memcpy(tx_array + 4, &(tx.data),    sizeof(u32));

You are copying to tx_array+2 twice.  I think you probably mean

    memcpy(tx_array + 0, &(tx.status),  sizeof(u16));

    memcpy(tx_array + 2, &(tx.command), sizeof(u16));

    memcpy(tx_array + 4, &(tx.address), sizeof(u16));

    memcpy(tx_array + 6, &(tx.data),    sizeof(u32));

The following also looks like it might be an error.  You are passing a pointer to a float cast to u32*.  Does your device really return a 32-bit float, or does it return an integer?

asynStatus PSController::readFloat64(asynUser* asyn, epicsFloat64* value)

{

      float temp = (float) *value;

      asynStatus status = performIO(asyn, (u32*) &temp);

      *value = temp;

      return status;

}

Neither of these problems is likely to cause the crash.  Please run the program under gdb and send the output of "backtrace" when it crashes.

Mark

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From: Abdalla Ahmad <Abdalla.Ahmad at sesame.org.jo>
Sent: Thursday, October 13, 2022 5:48 AM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>; Mark Rivers <rivers at cars.uchicago.edu>
Subject: Segmentation fault when using asyn Octect writeRead

 

Hello

 

I am writing a driver to control a custom power supply using asynPortDriver, I am using asynOctetSyncIO->writeRead interface to do IO with the controller but the IOC crashes on calling the function (https://github.com/AbdallaDalleh/psc-asyn-driver/blob/main/pscApp/src/PSController.cpp#L83 ). The asynOctetSyncIO interface crashes specifically on line 238, when casting the userPvt pointer of the passed asynUser pointer. I used this interface many times before and I have no idea why the segmentation fault happens.

 

Best Regards,

Abdalla.