mystrncat.c: (in function func)
mystrncat.c:12:13: Passed storage buffer not completely defined (*buffer is
                      undefined): mystrncat (buffer, ...)
mystrncat.c:13:13: Passed storage b not completely defined (*b is undefined):
                      mystrncat (b, ...)
   mystrncat.c:10:3: Storage *b allocated
mystrncat.c:12:3: Possible out-of-bounds store:
    mystrncat(buffer, str, sizeof((buffer)) - 1)
    Unable to resolve constraint:
    requires maxRead(buffer @ mystrncat.c:12:13) <= 0
     needed to satisfy precondition:
    requires maxSet(buffer @ mystrncat.c:12:13) >= maxRead(buffer @
    mystrncat.c:12:13) + 255
     derived from mystrncat precondition:
    requires maxSet(<parameter 1>) >= maxRead(<parameter 1>) + <parameter 3>
mystrncat.c:13:3: Possible out-of-bounds store:
    mystrncat(b, str, sizeof((buffer)) - 1)
    Unable to resolve constraint:
    requires maxRead(malloc(256) @ mystrncat.c:10:7) <= 0
     needed to satisfy precondition:
    requires maxSet(b @ mystrncat.c:13:13) >= maxRead(b @ mystrncat.c:13:13) +
    255
     derived from mystrncat precondition:
    requires maxSet(<parameter 1>) >= maxRead(<parameter 1>) + <parameter 3>

Finished checking --- 4 code warnings, as expected