Re: using skip>0 with bpf_get_stack()

[Eugene Loh <eugene.loh@oracle.com>]

No update from me.  A fix would be great.

On 3/4/22 3:37 PM, Namhyung Kim wrote:
> Hello,
>
> On Mon, Jun 28, 2021 at 08:33:11PM -0700, Yonghong Song wrote:
>>
>> On 6/25/21 6:22 PM, Eugene Loh wrote:
>>> On 6/1/21 5:48 PM, Yonghong Song wrote:
>>>> Could you submit a patch for this? Thanks!
>>> Sure.  Thanks for looking at this and sorry about the long delay getting
>>> back to you.
>>>
>>> Could you take a look at the attached, proposed patch?  As you see in
>>> the commit message, I'm unclear about the bpf_get_stack*_pe() variants.
>>> They might use an earlier construct callchain, and I do not know ho
>>> init_nr was set for them.
>> I think bpf_get_stackid() and __bpf_get_stackid() implementation is correct.
>> Did you find any issues?
>>
>> For bpf_get_stack_pe, see:
>>
>> https://lore.kernel.org/bpf/20200723180648.1429892-2-songliubraving@fb.com/
>> I think you should not change bpf_get_stack() function.
>> __bpf_get_stack() is used by bpf_get_stack() and bpf_get_stack_pe().
>> In bpf_get_stack_pe(), callchain is fetched by perf event infrastructure
>> if event->attr.sample_type & __PERF_SAMPLE_CALLCHAIN_EARLY is true.
>>
>> Just focus on __bpf_get_stack(). We could factor __bpf_get_stackid(),
>> but unless we have a bug, I didn't see it is necessary.
>>
>> It will be good if you can add a test for the change, there is a stacktrace
>> test prog_tests/stacktrace_map.c, you can take a look,
>> and you can add a subtest there.
>>
>> Next time, you can submit a formal patch with `git send-email ...` to
>> this alias. This way it is easier to review compared to attachment.
> Any updates on this?  I'm hitting the same issue and found this before
> sending a fix.
>
> Thanks,
> Namhyung