linux-kernel - Re: [PATCH 2/2] perf-probe: Change function definition check due to broken dwarf

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Date:   Fri, 27 Nov 2020 14:36:29 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Thomas Richter <tmricht@...ux.ibm.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sumanth Korikkar <sumanthk@...ux.ibm.com>
Subject: Re: [PATCH 2/2] perf-probe: Change function definition check due to
 broken dwarf

Em Fri, Nov 27, 2020 at 02:48:55PM +0900, Masami Hiramatsu escreveu:
> Since some gcc generates a broken DWARF which lacks DW_AT_declaration
> attribute from the subprogram DIE of function prototype.
> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97060)
> 
> So, in addition to the DW_AT_declaration check, we also check the
> subprogram DIE has DW_AT_inline or actual entry pc.

Thanks, applied and tested both patches on a fedora 33 system where
previously those tests were failing:

    Committer testing:

      # cat /etc/fedora-release
      Fedora release 33 (Thirty Three)
      #

    Before:

      # perf test vfs_getname
      78: Use vfs_getname probe to get syscall args filenames             : FAILED!
      79: Check open filename arg using perf trace + vfs_getname          : FAILED!
      81: Add vfs_getname probe to get syscall args filenames             : FAILED!
      #

    After:

      # perf test vfs_getname
      78: Use vfs_getname probe to get syscall args filenames             : Ok
      79: Check open filename arg using perf trace + vfs_getname          : Ok
      81: Add vfs_getname probe to get syscall args filenames             : Ok
      #


- Arnaldo
 
> Reported-by: Thomas Richter <tmricht@...ux.ibm.com>
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  tools/perf/util/dwarf-aux.c    |   20 ++++++++++++++++++--
>  tools/perf/util/probe-finder.c |    3 +--
>  2 files changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
> index 03c1a39c312a..7b2d471a6419 100644
> --- a/tools/perf/util/dwarf-aux.c
> +++ b/tools/perf/util/dwarf-aux.c
> @@ -356,9 +356,25 @@ bool die_is_signed_type(Dwarf_Die *tp_die)
>  bool die_is_func_def(Dwarf_Die *dw_die)
>  {
>  	Dwarf_Attribute attr;
> +	Dwarf_Addr addr = 0;
> +
> +	if (dwarf_tag(dw_die) != DW_TAG_subprogram)
> +		return false;
> +
> +	if (dwarf_attr(dw_die, DW_AT_declaration, &attr))
> +		return false;
>  
> -	return (dwarf_tag(dw_die) == DW_TAG_subprogram &&
> -		dwarf_attr(dw_die, DW_AT_declaration, &attr) == NULL);
> +	/*
> +	 * DW_AT_declaration can be lost from function declaration
> +	 * by gcc's bug #97060.
> +	 * So we need to check this subprogram DIE has DW_AT_inline
> +	 * or an entry address.
> +	 */
> +	if (!dwarf_attr(dw_die, DW_AT_inline, &attr) &&
> +	    die_entrypc(dw_die, &addr) < 0)
> +		return false;
> +
> +	return true;
>  }
>  
>  /**
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index 2c4061035f77..76dd349aa48d 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -1885,8 +1885,7 @@ static int line_range_search_cb(Dwarf_Die *sp_die, void *data)
>  	if (lr->file && strtailcmp(lr->file, dwarf_decl_file(sp_die)))
>  		return DWARF_CB_OK;
>  
> -	if (die_is_func_def(sp_die) &&
> -	    die_match_name(sp_die, lr->function)) {
> +	if (die_match_name(sp_die, lr->function) && die_is_func_def(sp_die)) {
>  		lf->fname = dwarf_decl_file(sp_die);
>  		dwarf_decl_line(sp_die, &lr->offset);
>  		pr_debug("fname: %s, lineno:%d\n", lf->fname, lr->offset);
> 

-- 

- Arnaldo