linux-kernel - Re: [PATCH v4] perf-probe: Support escaped character in parser

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Date:   Tue, 12 Dec 2017 12:27:24 -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>,
        Thomas Richter <tmricht@...ux.vnet.ibm.com>,
        linux-rt-users@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v4] perf-probe: Support escaped character in parser

Em Wed, Dec 13, 2017 at 12:05:12AM +0900, Masami Hiramatsu escreveu:
> Support the special characters escaped by '\' in parser.
> This allows user to specify versions directly like below.
> 
>   =====
>   # ./perf probe -x /lib64/libc-2.25.so malloc_get_state\\@GLIBC_2.2.5
>   Added new event:
>     probe_libc:malloc_get_state (on malloc_get_state@...BC_2.2.5 in /usr/lib64/libc-2.25.so)
> 
>   You can now use it in all perf tools, such as:
> 
> 	  perf record -e probe_libc:malloc_get_state -aR sleep 1
> 
>   =====
> 
> Or, you can use separators in source filename, e.g.
> 
>   =====
>   # ./perf probe -x /opt/test/a.out foo+bar.c:3
>   Semantic error :There is non-digit character in offset.
>     Error: Command Parse Error.
>   =====
> 
> Usually "+" in source file cause parser error, but
> 
>   =====
>   # ./perf probe -x /opt/test/a.out foo\\+bar.c:4
>   Added new event:
>     probe_a:main         (on @foo+bar.c:4 in /opt/test/a.out)
> 
>   You can now use it in all perf tools, such as:
> 
> 	  perf record -e probe_a:main -aR sleep 1
>   =====
> 
> escaped "\+" allows you to specify that.

<SNIP>

>  Changes in v4:
>   - Fix a build error (Thanks for Arnaldo!)
>     This time, I ensured that I ran "make build-test" and it passed.

Thanks, testing it I still have that artifact:

 ---------------------------------------

[root@...et perf]# perf probe -x /lib64/libc-2.25.so malloc_get_state\\@GLIBC_2.2.5
Added new event:
  probe_libc:malloc_get_state (on malloc_get_state@...BC_2.2.5 in /usr/lib64/libc-2.25.so)

You can now use it in all perf tools, such as:

	perf record -e probe_libc:malloc_get_state -aR sleep 1

[root@...et perf]# perf probe -l
Failed to find debug information for address dd38eca7
  probe_libc:malloc_get_state (on 0xdd38eca7 in /usr/lib64/libc-2.25.so)
[root@...et perf]#

 ---------------------------------------

I mean the "on 0xdd38eca7" part:

That failed to find debug information part:

[root@...et perf]# perf probe -vv -l
Add filter: *
Opening /sys/kernel/debug/tracing//kprobe_events write=0
Opening /sys/kernel/debug/tracing//uprobe_events write=0
Parsing probe_events: p:probe_libc/malloc_get_state /usr/lib64/libc-2.25.so:0x00000000dd38eca7
Group:probe_libc Event:malloc_get_state probe:p
try to find information at dd38eca7 in /usr/lib64/libc-2.25.so
Open Debuginfo file: /usr/lib/debug/usr/lib64/libc-2.25.so.debug
Failed to find debug information for address dd38eca7
Failed to find corresponding probes from debuginfo.
symsrc__init: build id mismatch for /usr/lib/debug/usr/lib64/libc-2.25.so.debug.
Failed to find probe point from both of dwarf and map.
  probe_libc:malloc_get_state (on 0xdd38eca7 in /usr/lib64/libc-2.25.so)
[root@...et perf]#

Ok, so build-id mismatch, lets see:

[root@...et perf]# rpm -q glibc glibc-debuginfo
glibc-2.25-10.fc26.x86_64
glibc-2.25-10.fc26.i686
glibc-debuginfo-2.25-12.fc26.x86_64
[root@...et perf]#

Ok, the debuginfo file is newer than the glibc installed, updating glibc
now...

We could have a more informative message in this case, right? I.e.
something like:

[root@...et perf]# perf probe -l
There was a build-id mismatch while trying to resolve 0xdd38eca7, please
check your system's debuginfo files for mismatches, e.g. check the
versions for glibc and glibc-debuginfo.
  probe_libc:malloc_get_state (on 0xdd38eca7 in /usr/lib64/libc-2.25.so)
[root@...et perf]#

- Arnaldo