debugging enabled? (was Re: KGDB command line options not working for kernel 2.6.32)

debugging enabled? (was Re: KGDB command line options not working for kernel 2.6.32)

[Mulyadi Santosa]

>I have one question in this context. Should we disable optimization when >building the kernel when we wish to enable kgdb or should we leave it intact.

Whenever possible, yes...disable optimization.... -O option and -g in
gcc don't play nicely together according to my experience. The DWARF
info will be somewhat fuzzed or even "corrupted"....so it might point
to wrong source line etc

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

debugging enabled? (was Re: KGDB command line options not working for kernel 2.6.32)

[Spiro Trikaliotis]

Hello,

* On Mon, Jun 27, 2011 at 09:51:53PM +0700 Mulyadi Santosa wrote:
> >I have one question in this context. Should we disable optimization when
> >building the kernel when we wish to enable kgdb or should we leave it intact.
> 
> Whenever possible, yes...disable optimization.... -O option and -g in
> gcc don't play nicely together according to my experience. The DWARF
> info will be somewhat fuzzed or even "corrupted"....so it might point
> to wrong source line etc

On the one hand, you are right. With optimisations on, following the
code lines does not give much fun. Some locals are not visible as they
are optimised out, and so on.

On the other hand: With optimisations disabled, the kernel behaves
differently than it would with optimisations. That's why many people
prefer to keep them switched on, and only disable them partially if
really, really needed.

Anyway, the opinions vary a lot here. I think one should try both and
find out what fits most to ones way of doing it.

Best regards
Spiro.

-- 
Spiro R. Trikaliotis                              http://opencbm.sf.net/
http://www.trikaliotis.net/                     http://www.viceteam.org/

debugging enabled? (was Re: KGDB command line options not working for kernel 2.6.32)

[Mulyadi Santosa]

Hi Spiro

On Tue, Jun 28, 2011 at 01:40, Spiro Trikaliotis
<ml-kernelnewbies@spiro.trikaliotis.net> wrote:
>
> On the other hand: With optimisations disabled, the kernel behaves
> differently than it would with optimisations. That's why many people
> prefer to keep them switched on, and only disable them partially if
> really, really needed.

I agree...even I still have mixed conclusion whether to go or no go
with -O when dealing with -O and debugging. I guess one of the biggest
offenders are: inlining, dead code (and symbols) elimination,
substitution with specific machine specific opcode (not really sure,
is -march has relationship with -O)...

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

debugging enabled? (was Re: KGDB command line options not working for kernel 2.6.32)

[Prabhu nath]

Hi Mulyadi/Spiro,

           Can you please help me in partially enabling/disabling
optimizations, because I was consistently hitting at the below problem when
building the kernel after disabling the optimization

ERROR: "intel_gmbus_is_forced_bit" [drivers/gpu/drm/i915/i915.ko] undefined!
ERROR: "__udivdi3" [drivers/gpu/drm/i915/i915.ko] undefined!
make[2]: *** [__modpost] Error 1
make[1]: *** [modules] Error 2
make: *** [sub-make] Error 2

Can I enable optimization for this i915 driver, so that I can contine with
my kernel building ?

Thanks,
Prabhu


On Tue, Jun 28, 2011 at 7:21 AM, Mulyadi Santosa
<mulyadi.santosa@gmail.com>wrote:

> Hi Spiro
>
> On Tue, Jun 28, 2011 at 01:40, Spiro Trikaliotis
> <ml-kernelnewbies@spiro.trikaliotis.net> wrote:
> >
> > On the other hand: With optimisations disabled, the kernel behaves
> > differently than it would with optimisations. That's why many people
> > prefer to keep them switched on, and only disable them partially if
> > really, really needed.
>
> I agree...even I still have mixed conclusion whether to go or no go
> with -O when dealing with -O and debugging. I guess one of the biggest
> offenders are: inlining, dead code (and symbols) elimination,
> substitution with specific machine specific opcode (not really sure,
> is -march has relationship with -O)...
>
> --
> regards,
>
> Mulyadi Santosa
> Freelance Linux trainer and consultant
>
> blog: the-hydra.blogspot.com
> training: mulyaditraining.blogspot.com
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
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debugging enabled? (was Re: KGDB command line options not working for kernel 2.6.32)

[Mulyadi Santosa]

Hi...

On Tue, Jun 28, 2011 at 13:25, Prabhu nath <gprabhunath@gmail.com> wrote:
> Hi Mulyadi/Spiro,
>
> ?????????? Can you please help me in partially enabling/disabling
> optimizations, because I was consistently hitting at the below problem when
> building the kernel after disabling the optimization
>
> ERROR: "intel_gmbus_is_forced_bit" [drivers/gpu/drm/i915/i915.ko] undefined!
> ERROR: "__udivdi3" [drivers/gpu/drm/i915/i915.ko] undefined!
> make[2]: *** [__modpost] Error 1
> make[1]: *** [modules] Error 2
> make: *** [sub-make] Error 2
>
> Can I enable optimization for this i915 driver, so that I can contine with
> my kernel building ?

Please don't top post.... btw, I remember that someone posted the same
problem about a week or two ago...kindly dig the archieve and see what
the solution is there. Sorry if I can't help much.

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
training: mulyaditraining.blogspot.com

debugging enabled? (was Re: KGDB command line options not working for kernel 2.6.32)

[Dave Hylands]

Hi Prabhu,

On Mon, Jun 27, 2011 at 11:25 PM, Prabhu nath <gprabhunath@gmail.com> wrote:
> Hi Mulyadi/Spiro,
>
> ?????????? Can you please help me in partially enabling/disabling
> optimizations, because I was consistently hitting at the below problem when
> building the kernel after disabling the optimization
>
> ERROR: "intel_gmbus_is_forced_bit" [drivers/gpu/drm/i915/i915.ko] undefined!
> ERROR: "__udivdi3" [drivers/gpu/drm/i915/i915.ko] undefined!
> make[2]: *** [__modpost] Error 1
> make[1]: *** [modules] Error 2
> make: *** [sub-make] Error 2

This is happening because some code is trying to do 64-bit division
which isn't supported in the kernel. The code needs to be modified to
use do_div macro (which is available in either asm/div64.h).

-- 
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com