Messages in this thread | | | Date | Thu, 12 May 2011 23:06:05 +0200 | From | Ingo Molnar <> | Subject | Re: [BUG] perf: bogus correlation of kernel symbols |
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* David Miller <davem@davemloft.net> wrote:
> From: Stephane Eranian <eranian@google.com> > Date: Thu, 12 May 2011 16:48:46 +0200 > > > I think there is a serious problem with kernel symbol correlation > > with the latest perf in 2.6.39-rc7-tip. > > The behavior seems to be intentional, so that we don't expose internal > kernel addresses to userspace. > > I hate this too, and I think it's absolutely rediculous. > > Also, like you, I lost an entire afternoon trying to figure out why > this started happening.
I lost about an hour with Arnaldo on IRC to help me until we figured out that /proc/kallsyms started having zero value entries ... I'm too running perf as an unprivileged user.
Zero is a valid symbol address so nothing within perf tripped up explicitly, but perf report and perf top results were nonsensical.
There was another problem with it: perf is caching and storing known kernel buildid addresses in ~/.debug, under the (previously correct) assumption that kernel symbols do not change for one given kernel build. But with kptr_restrict it would cache the zero values - which were cached even after kptr_restrict was set back to 0.
Thanks,
Ingo
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