Date: Thu, 30 May 1996 00:00:14 +0100 From: "Gary Palmer" <gpalmer@FreeBSD.ORG> To: grog@lemis.de (Greg Lehey) Cc: scrappy@ki.net (Marc G. Fournier), hackers@FreeBSD.ORG (FreeBSD Hackers) Subject: Re: I HATE OPTIMISING COMPILERS Message-ID: <2951.833410814@palmer.demon.co.uk> In-Reply-To: Your message of "Wed, 29 May 1996 18:52:09 %2B0200." <199605291652.SAA24396@allegro.lemis.de>
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Greg Lehey wrote in message ID
<199605291652.SAA24396@allegro.lemis.de>:
> At this point, of course, our mileage varies. Here, you would get the
> result:
> + (gdb) p pdu->version
> + $3 = -1
Sorry, BZZZZZZZT
The actual program, producing the actual results:
gdb apps/snmpwalk
GDB is free software and you are welcome to distribute copies of it
under certain conditions; type "show copying" to see the conditions.
There is absolutely no warranty for GDB; type "show warranty" for details.
GDB 4.13 (i386-unknown-freebsd),
Copyright 1994 Free Software Foundation, Inc...
(gdb) break snmp_api.c:1006
Breakpoint 1 at 0x96df: file snmp_api.c, line 1006.
(gdb) run -v 1 localhost public
Starting program: /mnt/root/usr/home/gary/ftp/ucd-snmp-3.1/apps/snmpwalk -v 1 localhost public
Breakpoint 1, snmp_send (session=0x65100, pdu=0x65180) at snmp_api.c:1007
1007 if (pdu->version == SNMP_DEFAULT_VERSION){
(gdb) print pdu->version
$1 = -1
(gdb) print session->version
$2 = 0
(gdb) break 1009
Breakpoint 2 at 0x96ef: file snmp_api.c, line 1009.
(gdb) cont
Continuing.
Breakpoint 2, snmp_send (session=0x65100, pdu=0x65180) at snmp_api.c:1010
1010 if (pdu->version == SNMP_DEFAULT_VERSION){
(gdb) print pdu->version
$3 = 0
(gdb) print session->version
$4 = 0
(gdb) s
1011 fprintf(stderr, "No version specified\n");
(gdb)
1013 return 0;
(gdb)
No version specified
1068 snmp_errno = SNMPERR_BAD_ADDRESS;
So, you see, GDB says that pdu->version does NOT equal
SNMP_DEFAULT_VERSION. I guess it would have tracked down the problem
quicker, but I STILL don't like gdb :-)
I guess it comes from a time when I tried (and NEARLY suceeded) in
porting the FreeBSD kernel to another machine ... printf was all I had
:-)
> I'd do this differently in gdb. Personally, I'd look at the code that
> was generated. Your code won't look like this, of course, because
> this code works. But you can see a few things:
Only if you read 80x86, which I don't, and probably never will. I've
been corrupted by a RISC processor, and hope never to have to touch a
CISC assembler ever again :-) I know (or used to) 6502 and 68000, and
that's plenty CISC to last enough a lifetime :-)
[SNIP]
> Reading assembler is tough, of course, but there are other ways. In
> any case, you save a lot by doing it this way rather than going and
> editing and recompiling possibly dozens of times.
Hmm. Maybe. Call me stoopid, but I still like my printf's thankyou :-)
Gary
--
Gary Palmer FreeBSD Core Team Member
FreeBSD: Turning PC's into workstations. See http://www.FreeBSD.ORG/ for info
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