linux-kernel - Re: [PATCH v3 1/6] perf: prepare perf_event.h for new types perf_kprobe and perf

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Date:   Mon, 4 Dec 2017 10:26:53 -0800
From:   Alexei Starovoitov <ast@...com>
To:     Song Liu <songliubraving@...com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v3 1/6] perf: prepare perf_event.h for new types
 perf_kprobe and perf_uprobe

On 12/4/17 10:24 AM, Song Liu wrote:
>
>> On Dec 3, 2017, at 9:03 AM, Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
>>
>> On Thu, Nov 30, 2017 at 03:50:18PM -0800, Song Liu wrote:
>>> Two new perf types, perf_kprobe and perf_uprobe, will be added to allow
>>> creating [k,u]probe with perf_event_open. These [k,u]probe are associated
>>> with the file decriptor created by perf_event_open, thus are easy to
>>> clean when the file descriptor is destroyed.
>>>
>>> kprobe_func and uprobe_path are added to union config1 for pointers to
>>> function name for kprobe or binary path for uprobe.
>>>
>>> kprobe_addr and probe_offset are added to union config2 for kernel
>>> address (when kprobe_func is NULL), or [k,u]probe offset.
>>>
>>> Signed-off-by: Song Liu <songliubraving@...com>
>>> Reviewed-by: Yonghong Song <yhs@...com>
>>> Reviewed-by: Josef Bacik <jbacik@...com>
>>> Acked-by: Alexei Starovoitov <ast@...nel.org>
>>> ---
>>> include/uapi/linux/perf_event.h | 6 ++++++
>>> 1 file changed, 6 insertions(+)
>>>
>>> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
>>> index 362493a..247c6cb 100644
>>> --- a/include/uapi/linux/perf_event.h
>>> +++ b/include/uapi/linux/perf_event.h
>>> @@ -299,6 +299,8 @@ enum perf_event_read_format {
>>> #define PERF_ATTR_SIZE_VER4	104	/* add: sample_regs_intr */
>>> #define PERF_ATTR_SIZE_VER5	112	/* add: aux_watermark */
>>>
>>> +#define MAX_PROBE_FUNC_NAME_LEN 64
>>
>> I think we have to remove this restriction.
>> There are already functions with names longer than 64 characters
>> in the current vmlinux:
>> trace_event_define_fields_ext4_ext_convert_to_initialized_fastpath
>> trace_event_define_fields_mm_vmscan_direct_reclaim_begin_template
>>
>> How about we drop this restriction and use NAME_MAX internally
>> without adding new uapi defines ?
>
> Yeah, I agree that we should drop this uapi define. How about we use
>
> #define KSYM_NAME_LEN 128
>
> If a function name is longer than KSYM_NAME_LEN, we get warning like:
>
> Symbol long_long_name_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz_abcdefghijklmnopqrstuvwxyz_ too long for kallsyms (204 vs 128).
> Please increase KSYM_NAME_LEN both in kernel and kallsyms.c

right. that's better.
Thanks