Re: [gentoo-embedded] lockups with hardened kernel

[Natanael Copa <mlists@tanael.org>]

On man, 2006-01-09 at 17:20 +0100, Peter S. Mazinger wrote:
> On Sat, 7 Jan 2006, Mike Frysinger wrote:
> 
> > On Saturday 07 January 2006 02:30, Natanael Copa wrote:
> > > On lør, 2006-01-07 at 00:44 -0500, Mike Frysinger wrote:
> > > > On Wednesday 04 January 2006 03:52, Natanael Copa wrote:
> > > > > I got a report from someone who experienced lockups when using
> > > > > gentoo-embedded built system (2.6.14-hardened-r1)

> > > When I disabled "Configure standard kernel features (for small
> > > systems)" (gcc -Os) the problem magically went away.
> > 
> > the kernel can be pretty sensitive to optimizations
> 
> if kernel is built w/ gcc-3.4.4 and -Os (at least I had that for 2.4.x 
> kernels) it "optimizes away" memcmp and the kernels have gotten a patch 
> to overcome this, the same problem does not occur w/ gcc-3.3.x.
> 
> > > So I think its a bug in gcc version 3.4.4 (Gentoo Hardened 3.4.4-r1,
> > > ssp-3.4.4-1.0, pie-8.7.8)
> > >
> > > Makes me nervous because I have built everything with -Os.
> 
> I have built everything w/ -Os and do not have trouble w/ it

I have researched this and found out that it is not the -Os itself that
causes this, but it is something else under "Configure standard kernel
features (for small systems)". I'm not sure of exactly what but I know
at least that it is not "Optimize for size". I have turned all options
under "Configure standard kernel features (for small systems)" except
"Load all symbols for debugging/kksymoops" (including optimize for size
(-Os)) and done the netload test all night. This morning the computer
was still up.  When I have an unstable kernel it hangs after an hour or
two.

I have tried to flip the "futex support" and that did not make any
difference (anyone who know how this affects uclibc based apps btw? Do I
need futex support?)

I think I have narrowed down the problem to one of those:
* BUG() support
* Enable full-sized data structures for core
* Enable eventpoll support

But exactly what, I dont know. If anyone here have had any problems with
disabling one of those, I'm very interested to hear.

Lots of bla bla here, I just thought it could be good for you guys to
know that turning off of those might make your kernel unstable, while
-Os should be ok with current gcc.


-- 
Natanael Copa

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