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

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Message-ID: <20150306180226.GB5187@kernel.org>
Date:	Fri, 6 Mar 2015 15:02:26 -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 02:59:19PM -0300, Arnaldo Carvalho de Melo escreveu:
> 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:

Ok, it works after applying 2/5, so it was just me confused by the above
statement, that a fallback was added that would make --lines work, it
works, but not with this patch, the next one is needed.

Anyway, works now, I'm happy, thanks!

- Arnaldo
 
> [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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