"fast data access mmu miss" on kernels w/o "makeoptions DEBUG=-g"

[Marius Strobl]

On Mon, Aug 15, 2005 at 10:42:36AM -0400, John Nielsen wrote:
> On Friday 12 August 2005 00:53, Andrew Belashov wrote:
> > John Nielsen wrote:
> > > Can anyone say why removing "makeoptions DEBUG=-g" from a kernel would
> > > make it unreliable?  I'm on an Ultra 5, and it's quite stable with
> > > either GENERIC or the kernel specified below.  However, commenting out
> > > the "makeoptions DEBUG=-g" line builds a kernel that boots but then
> > > panics right after mounting /:
> > >
> > > Entropy harvesting: interrupts ethernet point_to_pointpanic: trap: fast
> > > data access mmu miss
> > > Uptime:2s
> > > Dumping 512 MB (2 chunks)
> >
> > Try to clean rebuild kernel (remove build directory
> > /usr/obj/usr/src/sys/KERNCONF or /sys/compile/KERNCONF).
> 
> No change even after a fresh buildworld (using RELENG_6):
> 
> cvsup /etc/supfile-src && rm -r /usr/obj/* && cd /usr/src && make make && 
> make clean && make cleandir && make cleandir && make buildworld && make 
> buildkernel && make installkernel && make installworld && mergemaster
> 
> I don't mind leaving the option in the kernel, but it does seem like a 
> strange bug.  Let me know if anyone has any other ideas.  Thanks,
> 

When the DEBUG make option is defined the compiler optimization
flags (COPTFLAGS) default to '-O -pipe' whereas without DEBUG the
default is '-O2 -pipe' ('-O2' can cause bogus stack traces so it's
not the default for debugging kernels). So in case you also get a
panic with a kernel having both:
makeoptions	DEBUG=-g
and:
makeoptions	COPTFLAGS="-O2 -pipe"
this probably means that there's bogus code that breaks at higher
optimization levels or a compiler bug. A stack trace from such a
panic might help to track this down in case it's not screwed due
to the '-O2'.

Marius