[Info-vax] %SYSTEM-F-ACCVIO in LIBOTS after several hours

[Simon Clubley]

On 2022-03-08, Mark Daniel <mark.daniel at wasd.vsm.com.au> wrote:
> Reproducible after several hours of continuous execution.
>
>> %SYSTEM-F-ACCVIO, access violation, reason mask=04, virtual address=0000000000039B00, PC=FFFFFFFF842341D0, PS=0000001B
>> %TRACE-F-TRACEBACK, symbolic stack dump follows
>> image     module    routine               line      rel PC           abs PC
>> LIBOTS                                       0 00000000000121D0 FFFFFFFF842341D0
>> DECC$SHR  C$TXDOPRINT  putbuf            43567 000000000000CA82 FFFFFFFF84BC4FA2
>> DECC$SHR  C$TXDOPRINT  decc$$txdoprint   43658 000000000000CD62 FFFFFFFF84BC5282
>> DECC$SHR  C$TXDOPRINT  sprintf           44192 0000000000012492 FFFFFFFF84BCA9B2
>> HTTPDMON  HTTPDMON  TcpIpLookup          60709 00000000000109A2 00000000000409A2
>> HTTPDMON  HTTPDMON  AddRequest           60536 0000000000009A62 0000000000039A62
>> HTTPDMON  HTTPDMON  MonitorHttpd         58867 0000000000001392 0000000000031392
>> HTTPDMON  HTTPDMON  main                 58751 0000000000000962 0000000000030962
>> HTTPDMON  HTTPDMON  __main               58666 00000000000000B2 00000000000300B2
>>                                              0 FFFFFFFF80A37952 FFFFFFFF80A37952
>> DCL                                          0 000000000007D2B2 000000007AE292B2
>> %TRACE-I-END, end of TRACE stack dump
>
> Line 60790 is
>
>>       3   60709             sprintf (ares[aCacheIdx], "[%s]", strerror(errno));
>

[snip]

>
> The ACCVIO is related to the target, ares[aCacheIdx], or to the 
> argument, strerror(errno)), or...?
>
> TIA for any input.
>

Since no-one else has replied, some generic observations:

Given the address and reason mask, it looks like something is trying to
write into what looks like RO program code.

Does changing the optimisation level (or disabling optimisation) change
the behaviour ?

Don't assume errno is valid or that strerror() has behaved in an
intelligent way if it has been presented with an invalid errno value.

Can you take an image dump when the program crashes and then look around
the general area of the failing VA to see if there are any clues about
what is at that location ?

Are you sure that ares[aCacheIdx] points to a memory location big enough
to hold the message ? Before that line of code is executed, you could
try writing to a temporary file both errno and the length of the output
from strerror(). Also try dumping the current value of aCacheIdx to that
file.

This has the feel of some out-of-bounds write. Whether that's due to a
VMS issue or your code I can't tell.

Also, consider the use of snprintf() instead of sprintf() if it is
available to you. That line of code looks like an error reporting
version of an unbounded strcpy() call and there's a reason why
strncpy() and friends now exist. :-)

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Walking destinations on a map are further away than they appear.