cvs commit: src/etc/defaults rc.conf

[Dmitry Pryanishnikov]

Hello!

On Wed, 23 Apr 2008 John Baldwin wrote:
>> brooks      2008-04-21 18:17:48 UTC
>>
>>   FreeBSD src repository
>>
>>   Modified files:
>>     etc/defaults         rc.conf
>>   Log:
>>   Change the default of ddb_enable to YES so we default to generating
>> textdumps on panic.  This means you get a potentially useful dump even if
>> your system is running X when you panic.
>
> Note that for many panics (such as page faults due to a NULL pointer
> dereference) the enhanced stack handling ability of kgdb (ability to examine
> local variables in stack frames, etc.) is a lot more useful than ddb and now
> those panics won't be nearly as easy to debug via textdumps.
>
> As far as panics in X are concerned, that is a bug in the console driver that
> it doesn't just abort ddb already and write out a dump and reboot.  I've been
> disabling ddb on panics via tunable as a workaround on my laptop to get
> crashdumps during panics in X.

 Indeed, I haven't missed a single crash dump since addition of

debug.debugger_on_panic=0

to /etc/sysctl.conf on my Asus M5A. That crashes occur now and again
due to usb/116561
(previously in RELENG_6, now in RELENG_7) almost always during web browsing in X
while using CDMA USB modem.

 I also think that textdumps severely limit amount of available
debugging information
as compared with ordinary memory [mini]dump. I don't think one can reliably
and universally foresee which variables/structures should be dumped by
ddb scripts;
and once you don't have access to some specific piece of info in
textdump, you can't proceed with the debugging. There is no such
problem with ordinary dumps as they contain all information available
at the moment of the crash.

-- 
Sincerely, Dmitry
nic-hdl: LYNX-RIPE