Re: 2.6.15-rt4 failure with LATENCY_TRACE on x86_64

[Mikael Andersson <mikael@karett.se>]

Steven Rostedt wrote:
> On Fri, 13 Jan 2006, Clark Williams wrote:
>>Have you tried booting your system with a up kernel?
>>
> Not a x86_64 up.  But serveral up i386 boxes.
> 

I had a very similar problem on a x86_64 up. I got a segfault in init 
with LATENCY_TRACE enabled on 2.6.15-rt2.
I get it at ffffffff8010fe30, which should be mcount according to my 
System.map [1]. It seems a bit weird because i have tried to alter 
mcount somewhat. Initially by removing the initial comparison, but later
i tried a few other things also. Nothing had any effect at all.

AFAIK glibc also has a mcount symbol, and it's almost as if ld.so would 
have linked the glibc mcount symbol to the kernel symbol mcount. That
would naturally lead to a pagefault :)
  And it would be consistent with the fact that statically linked shells
works.

It's probably something completely different, bevause that would be 
really weird. OTOH, it was really weird that i could change the asm for 
mcount in entry.S without any effect whatsoever.

I'll verify that it hasn't gone away in lates 2.6.15-rt tomorrow.

[1]
ffffffff8010fd68 T machine_check
ffffffff8010fdf0 T call_debug
ffffffff8010fe00 T call_softirq
ffffffff8010fe30 T mcount
ffffffff8010fe65 t skiptrace
ffffffff8010fe7c t out

/Mikael