linux-kernel - Re: [PATCH v2 2/5] perf-probe: Cut off the version suffix from event name

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Date:   Thu, 7 Dec 2017 11:24:47 -0600
From:   Paul Clarke <pc@...ibm.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Cc:     bhargavb <bhargavaramudu@...il.com>, linux-kernel@...r.kernel.org,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>,
        linux-rt-users@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2 2/5] perf-probe: Cut off the version suffix from event
 name



On 12/07/2017 10:56 AM, Arnaldo Carvalho de Melo wrote:
> Em Thu, Dec 07, 2017 at 04:20:28PM +0900, Masami Hiramatsu escreveu:
>> Cut off the version suffix (e.g. @GLIBC_2.2.5 etc.) from
>> automatic generated event name. This fixes wildcard event
>> adding like below case;
>>
>>   =====
>>   # perf probe -x /lib64/libc-2.25.so malloc*
>>   Internal error: "malloc_get_state@...BC_2" is wrong event name.
>>     Error: Failed to add events.
>>   =====
>>
>> This failure was caused by a versioned suffix symbol.
>> With this fix, perf probe automatically cuts the
>> suffix after @ as below.
>>
>>   =====
>>   # ./perf probe -x /lib64/libc-2.25.so malloc*
>>   Added new events:
>>     probe_libc:malloc_printerr (on malloc* in /usr/lib64/libc-2.25.so)
>>     probe_libc:malloc_consolidate (on malloc* in /usr/lib64/libc-2.25.so)
>>     probe_libc:malloc_check (on malloc* in /usr/lib64/libc-2.25.so)
>>     probe_libc:malloc_hook_ini (on malloc* in /usr/lib64/libc-2.25.so)
>>     probe_libc:malloc    (on malloc* in /usr/lib64/libc-2.25.so)
>>     probe_libc:malloc_trim (on malloc* in /usr/lib64/libc-2.25.so)
>>     probe_libc:malloc_usable_size (on malloc* in /usr/lib64/libc-2.25.so)
>>     probe_libc:malloc_stats (on malloc* in /usr/lib64/libc-2.25.so)
>>     probe_libc:malloc_info (on malloc* in /usr/lib64/libc-2.25.so)
>>     probe_libc:mallochook (on malloc* in /usr/lib64/libc-2.25.so)
>>     probe_libc:malloc_get_state (on malloc* in /usr/lib64/libc-2.25.so)
>>     probe_libc:malloc_set_state (on malloc* in /usr/lib64/libc-2.25.so)
> 
> Thanks for working on this! I'm now going over it, and one thing I
> noticed was that the (on malloc*) on all the entries matched by that
> wildcard, can I suggest that you expand it there as well? I.e.
> 
>      probe_libc:malloc_set_state (on malloc_set_state in /usr/lib64/libc-2.25.so)
> 
> This way we'll now when aliases are used, and also for the versioning
> case, i.e. to which version is a probe pointing?
> 
> See also Paul Clarke's question and suggestion, which I agree, i.e.
> instead of chopping off the version, just replace the chars with valid
> ones or better, do what Paul suggests, be more flexible in interpreting
> @, i.e. if it is a number and/or fails to point to any file, interpret
> it as versioning.

It's a nit, and subjective, but I'd favor checking for versioning first, then file.  The namespaces are very unlikely to intersect, but I could foresee symbols like "sym@...lA.c" and "sym@...lB.c" more likely than a symbol in a file "GLIBC_2.2.5".

Perhaps straying toward bikeshedding...

PC