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

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Date:   Fri, 8 Dec 2017 12:01:48 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Paul Clarke <pc@...ibm.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        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 Thu, 7 Dec 2017 10:34:51 -0600
Paul Clarke <pc@...ibm.com> wrote:

> 
> 
> On 12/07/2017 01:20 AM, Masami Hiramatsu wrote:
> > 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)
> > 
> >   You can now use it in all perf tools, such as:
> > 
> > 	  perf record -e probe_libc:malloc_set_state -aR sleep 1
> > 
> >   =====
> 
> I think this will still fall over for a case where there are multiple versions of the same base symbol, like:
> 
> $ nm /lib64/libc.so.6 | egrep ' sched_getaffinity'
> 0000000000134430 T sched_getaffinity@...BC_2.3.3
> 00000000000dcf00 T sched_getaffinity@@GLIBC_2.3.4

No, in that case perf probe adds number suffix (_1, _2...) for new events :)

This feature (number suffix) is anyway required for the case that inlined
function is spreaded in multiple places. I think this is natural for perf probe.

Thank you,

> 
> Should we retain the versioning string in some form?  "sched_getaffinity--GLIBC_2.3.4"?  Should we instead interpret the '@' symbol more flexibly, so maybe first assume it is a version string, and if not found, try to see if it's a valid "@SRC" specification?
> 
> PC
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>