linux-kernel - Re: [PATCH perf/core 1/2] [BUGFIX] perf-probe: Fix to handle optimized not-inlined but has no instance

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Date:	Fri, 30 Jan 2015 11:21:35 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, namhyung@...nel.org,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH perf/core 1/2] [BUGFIX] perf-probe: Fix to handle
 optimized not-inlined but has no instance

Em Fri, Jan 30, 2015 at 06:37:44PM +0900, Masami Hiramatsu escreveu:
> Fix to handle optimized no-inline functions which have
> only function definition but no actual instance at
> that point. To fix this problem, we need to find actual
> instance of the function.
> 
> Without this patch:
>   ----
>   # perf probe -a __up
>   Failed to get entry address of __up.
>     Error: Failed to add events.
>   # perf probe -L __up
>   Specified source line is not found.
>     Error: Failed to show lines.
>   ----
> 
> With this patch:
>   ----
>   # perf probe -a __up
>   Added new event:
>     probe:__up           (on __up)
> 
>   You can now use it in all perf tools, such as:
> 
>           perf record -e probe:__up -aR sleep 1
> 
>   # perf probe -L __up
>   <__up@...me/fedora/ksrc/linux-3/kernel/locking/semaphore.c:0>
>         0  static noinline void __sched __up(struct semaphore *sem)
>            {
>                   struct semaphore_waiter *waiter = list_first_entry(&sem->wait_
>                                                           struct semaphore_waite
>         4         list_del(&waiter->list);
>         5         waiter->up = true;
>         6         wake_up_process(waiter->task);
>         7  }
>   ----

Since __up here was built in some other way, I looked for another
'noinline' function to try, and it failed here:

  [root@zoo ~]# perf probe -L vmalloc_fault | head -5
  <vmalloc_fault@...me/git/linux/arch/x86/mm/fault.c:0>
        0  static noinline int vmalloc_fault(unsigned long address)
        1  {
           	pgd_t *pgd, *pgd_ref;
           	pud_t *pud, *pud_ref;
  [root@zoo ~]# perf probe vmalloc_fault
  Added new event:
  Failed to write event: Invalid argument
    Error: Failed to add events.

---->>>>>> APPLY THE PATCH, rebuild and try again:

  [root@zoo ~]# perf probe vmalloc_fault
  Added new event:
  Failed to write event: Invalid argument
    Error: Failed to add events.
  [root@zoo ~]# perf probe -v vmalloc_fault
  probe-definition(0): vmalloc_fault 
  symbol:vmalloc_fault file:(null) line:0 offset:0 return:0 lazy:(null)
  0 arguments
  Looking at the vmlinux_path (7 entries long)
  Using /lib/modules/3.19.0-rc6+/build/vmlinux for symbols
  Open Debuginfo file: /lib/modules/3.19.0-rc6+/build/vmlinux
  Try to find probe point from debuginfo.
  Probe point found: vmalloc_fault+0
  Found 1 probe_trace_events.
  Opening /sys/kernel/debug/tracing/kprobe_events write=1
  Added new event:
  Writing event: p:probe/vmalloc_fault _text+289600
  Failed to write event: Invalid argument
    Error: Failed to add events. Reason: Invalid argument (Code: -22)
  [root@zoo ~]# grep -w vmalloc_fault /proc/kallsyms
  ffffffff81046b40 t vmalloc_fault
  [root@zoo ~]# grep -w _text /proc/kallsyms 
  ffffffff81000000 T _text
  [root@zoo ~]# python 
  Python 2.7.5 (default, Nov  3 2014, 14:26:24) 
  [GCC 4.8.3 20140911 (Red Hat 4.8.3-7)] on linux2
  Type "help", "copyright", "credits" or "license" for more information.
  >>> 0xffffffff81046b40 - 0xffffffff81000000
  289600L
  >>> 
  [root@zoo ~]# readelf -s /lib/modules/3.19.0-rc6+/build/vmlinux | egrep -w _text\|vmalloc_fault
    3499: ffffffff81046b40   410 FUNC    LOCAL  DEFAULT    1 vmalloc_fault
   48873: ffffffff81000000     0 NOTYPE  GLOBAL DEFAULT    1 _text
  [root@zoo ~]# 

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

So perhaps I need a 'noinline' _and_ '__sched', so that I have a "optimized
no-inline functions which have only function definition but no actual instance
at that point"?

Looking for one, will post here after objdump -dS finishes...

- Arnaldo
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