Re: [PATCH] perf tools: Fix not finding kcore in buildid cache

Adrian Hunter
2013-11-27T08:10:54Z

On 26/11/13 18:15, Ingo Molnar wrote:
>
> * Adrian Hunter <adrian.hunter@intel.com> wrote:
>
>> The logic was not looking in the buildid cache for kcore
>> if the host kernel buildid did not match the recorded
>> kernel buildid.
>
> It would be nice to also include the specific failure mode in the
> changelog: exactly how can users run into this. That will be more
> useful to most people reading these changelogs than a more abstract
> bug description.

The preconditions for the problem are that kcore is in the buildid
cache and that the running kernel has a different buildid e.g.

$ perf buildid-list | grep kernel.kallsyms
b18fbe769dea12513028a4287dae02efc1582c29 [kernel.kallsyms]

$ perf record -o /tmp/junk true >/dev/null 2>&1 ; perf buildid-list -i /tmp/junk | grep kernel.kallsyms
504f9fd9328c40714995ce76fe1354c6e90136ce [kernel.kallsyms]

Before the patch:

$ perf script -v >out.txt
build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
<SNIP>
Using /home/ahunter/.debug/[kernel.kallsyms]/b18fbe769dea12513028a4287dae02efc1582c29 for symbols

perf script stopped

After the patch:

$ perf script -v >out.txt
build id event received for [kernel.kallsyms]: b18fbe769dea12513028a4287dae02efc1582c29
<SNIP>
Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kcore for kernel object code
Using /home/ahunter/.debug/[kernel.kcore]/b18fbe769dea12513028a4287dae02efc1582c29/2013112617084061/kallsyms for symbols

perf script stopped