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

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Message-Id: <dd7ab590-f5bc-e7bb-6807-210c099072fe@us.ibm.com>
Date:   Thu, 7 Dec 2017 10:34:51 -0600
From:   Paul Clarke <pc@...ibm.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...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 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

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