linux-kernel - Re: [PATCH perf/core v2 1/5] perf-probe: Fix to handle aliased symbols in glibc

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Message-ID: <20150306175919.GA5187@kernel.org>
Date:	Fri, 6 Mar 2015 14:59:19 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Naohiro Aota <naota@...sp.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>, namhyung@...nel.org,
	Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH perf/core v2 1/5] perf-probe: Fix to handle aliased
 symbols in glibc

Em Fri, Mar 06, 2015 at 04:31:20PM +0900, Masami Hiramatsu escreveu:
> Fix perf probe to handle aliased symbols correctly in glibc.
> In the glibc, several symbols are defined as an alias of
> __libc_XXX, e.g. malloc is an alias of __libc_malloc.
> In such cases, dwarf has no subroutine instances of the
> alias functions (e.g. no "malloc" instance), but the map
> has that symbol and its address.
> Thus, if we search the alieased symbol in debuginfo, we
> always fail to find it, but it is in the map.
> 
> To solve this problem, this fails back to address-based
> alternative search, which searches the symbol in the map,
> translates its address to alternative (correct) function
> name by using debuginfo, and retry to find the alternative
> function point from debuginfo.
> 
> This adds fail-back process to --vars, --lines and --add
> options. So, now you can use those on malloc@...c :)

--vars and --add works, but not --lines:

[root@...andy ~]# perf probe -x /usr/lib64/libc-2.17.so -V malloc
Available variables at malloc
        @<__libc_malloc+96>
                size_t  bytes

[root@...andy ~]# perf probe -x /usr/lib64/libc-2.17.so -L malloc
Specified source line is not found.
  Error: Failed to show lines.
[root@...andy ~]# 

[root@...andy ~]# perf probe -x /usr/lib64/libc-2.17.so -a "malloc
bytes"
Added new event:
  probe_libc:malloc    (on malloc in /usr/lib64/libc-2.17.so with bytes)

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

	perf record -e probe_libc:malloc -aR sleep 1

[root@...andy ~]#

[root@...andy ~]# cat /t/events/probe_libc/malloc/format 
name: malloc
ID: 1921
format:
	field:unsigned short common_type;	offset:0;	size:2;	signed:0;
	field:unsigned char common_flags;	offset:2;	size:1;	signed:0;
	field:unsigned char common_preempt_count;	offset:3;	size:1;	signed:0;
	field:int common_pid;	offset:4;	size:4;	signed:1;

	field:unsigned long __probe_ip;	offset:8;	size:8;	signed:0;
	field:u64 bytes;	offset:16;	size:8;	signed:0;

print fmt: "(%lx) bytes=0x%Lx", REC->__probe_ip, REC->bytes
[root@...andy ~]# 

Works for the aliased symbol, anyway, applying as it makes progress.

[root@...andy ~]# perf probe -x /usr/lib64/libc-2.17.so -L __libc_malloc
<__libc_malloc@...r/src/debug/glibc-2.17-c758a686/malloc/malloc.c:0>
      0  __libc_malloc(size_t bytes)
      1  {
           mstate ar_ptr;
           void *victim;
         
           __malloc_ptr_t (*hook) (size_t, const __malloc_ptr_t)
      6      = force_reg (__malloc_hook);
      7    if (__builtin_expect (hook != NULL, 0))
      8      return (*hook)(bytes, RETURN_ADDRESS (0));
         
     10    arena_lookup(ar_ptr);
         
     12    arena_lock(ar_ptr, bytes);
     13    if(!ar_ptr)
     14      return 0;
     15    victim = _int_malloc(ar_ptr, bytes);
     16    if(!victim) {
     17      LIBC_PROBE (memory_malloc_retry, 1, bytes);
     18      ar_ptr = arena_get_retry(ar_ptr, bytes);
     19      if (__builtin_expect(ar_ptr != NULL, 1)) {
     20        victim = _int_malloc(ar_ptr, bytes);
     21        (void)mutex_unlock(&ar_ptr->mutex);
             }
           } else
     24      (void)mutex_unlock(&ar_ptr->mutex);
           assert(!victim || chunk_is_mmapped(mem2chunk(victim)) ||
                 ar_ptr == arena_for_chunk(mem2chunk(victim)));
           return victim;
     28  }
         libc_hidden_def(__libc_malloc)
         
         void

[root@...andy ~]#
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