RE: Segmentation fault when using asyn Octect writeRead

[Abdalla Ahmad via Tech-talk <tech-talk at aps.anl.gov>]

Hello Mark

 

Yes that was an indexing mistake but it did not work. The device returns all readings, float and integer, as a raw unsigned 32-bit integer and then I cast the raw data pointer into float pointer if needed. I did ran the IOC under GDB and it crashes on the call to writeRead, exactly at line 238 in asynOctetSyncIO.c where it tries to cast the userPvt pointer of the asynUser to ioPvt*.

 

Best Regards,

Abdalla.

 

From: Mark Rivers <rivers at cars.uchicago.edu>
Sent: Thursday, October 13, 2022 3:09 PM
To: Abdalla Ahmad <Abdalla.Ahmad at sesame.org.jo>; tech-talk at aps.anl.gov
Subject: Re: Segmentation fault when using asyn Octect writeRead

 

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.