Experimental Physics and
Industrial Control System

    char                zrst[26];   /* Zero String */

    char                onst[26];   /* One String */

    char                twst[26];   /* Two String */

    char                thst[26];   /* Three String */

    char                frst[26];   /* Four String */

    char                fvst[26];   /* Five String */

    char                sxst[26];   /* Six String */

    char                svst[26];   /* Seven String */

    char                eist[26];   /* Eight String */

    char                nist[26];   /* Nine String */

    char                test[26];   /* Ten String */

    char                elst[26];   /* Eleven String */

    char                tvst[26];   /* Twelve String */

    char                ttst[26];   /* Thirteen String */

    char                ftst[26];   /* Fourteen String */

    char                ffst[26];   /* Fifteen String */

In function ‘setEnums.constprop’,

    inlined from ‘interruptCallbackEnumBi’ at ../../asyn/devEpics/devAsynInt32.c:760:5:

../../asyn/devEpics/devAsynInt32.c:445:25: warning: ‘strncpy’ forming offset [27, 51] is out of the bounds [0, 26] [-Warray-bounds]

         if (outStrings) strncpy((*outStrings)[i], inStrings[i], MAX_ENUM_STRING_SIZE-1);

                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In function ‘setEnums.constprop’,

    inlined from ‘interruptCallbackEnumBo’ at ../../asyn/devEpics/devAsynInt32.c:774:5:

../../asyn/devEpics/devAsynInt32.c:445:25: warning: ‘strncpy’ forming offset [27, 51] is out of the bounds [0, 26] [-Warray-bounds]

         if (outStrings) strncpy((*outStrings)[i], inStrings[i], MAX_ENUM_STRING_SIZE-1);

                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The warning is this:


[epics@viper asyn]$ make -s
In function ‘setEnums.constprop’,
   inlined from ‘interruptCallbackEnumBi’ at ../../asyn/devEpics/devAsynInt32.c:759:5:
../../asyn/devEpics/devAsynInt32.c:444:25: warning: ‘strncpy’ forming offset [27, 51] is out of the bounds [0, 26] [-Warray-bounds]
        if (outStrings) strncpy(&outStrings[i*MAX_ENUM_STRING_SIZE], inStrings[i], MAX_ENUM_STRING_SIZE-1);

So the compiler thinks I am passing an array of 26 byes, and so complains that I am writing to bytes 27 to 51. But actually I know that the array I am writing to is not really just 26 bytes long, it is actually larger. How do I communicate that knowledge to the compiler?

Mark

Sent from my iPhone

On Sep 16, 2020, at 8:37 PM, Chris Johns <chrisj at rtems.org> wrote:

On 17/9/20 11:28 am, Mark Rivers wrote:
That article is interesting but is about string truncation.  The warnings I am worried about are actually incorrectly flagging buffer overflow. I am hoping there is a cast or other method to avoid them.

OK, I am not across the full context. Reviewing the suggested patch the post
hinted that GCC looks for the terminating nul being written:

if (outStrings) {
strncpy(&outStrings[i*MAX_ENUM_STRING_SIZE], inStrings[i], MAX_ENUM_STRING_SIZE);
outStrings[i*MAX_ENUM_STRING_SIZE + MAX_ENUM_STRING_SIZE-1] = '\0';
}

New string functions in base don’t really help me since asyn needs to build, preferably without such warnings, on older versions of base.

That makes things harder.

Chris