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 13:56:59 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     bhargavb <bhargavaramudu@...il.com>, linux-kernel@...r.kernel.org,
        Paul Clarke <pc@...ibm.com>,
        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

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.

- Arnaldo

>   You can now use it in all perf tools, such as:
> 
> 	  perf record -e probe_libc:malloc_set_state -aR sleep 1
> 
>   =====
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> Reported-by: Arnaldo Carvalho de Melo <acme@...nel.org>
> Reported-by: bhargavb <bhargavaramudu@...il.com>
> ---
>  tools/perf/util/probe-event.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index c0067950e56f..74435fb7ab7f 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -2584,8 +2584,8 @@ static int get_new_event_name(char *buf, size_t len, const char *base,
>  	if (!nbase)
>  		return -ENOMEM;
>  
> -	/* Cut off the dot suffixes (e.g. .const, .isra)*/
> -	p = strchr(nbase, '.');
> +	/* Cut off the dot suffixes (e.g. .const, .isra) and version suffixes */
> +	p = strpbrk(nbase, ".@");
>  	if (p && p != nbase)
>  		*p = '\0';
>