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    Subject[PATCH 4.14 105/161] perf probe: Skip end-of-sequence and non statement lines
    Date
    From: Masami Hiramatsu <mhiramat@kernel.org>

    [ Upstream commit f4d99bdfd124823a81878b44b5e8750b97f73902 ]

    Skip end-of-sequence and non-statement lines while walking through lines
    list.

    The "end-of-sequence" line information means:

    "the current address is that of the first byte after the
    end of a sequence of target machine instructions."
    (DWARF version 4 spec 6.2.2)

    This actually means out of scope and we can not probe on it.

    On the other hand, the statement lines (is_stmt) means:

    "the current instruction is a recommended breakpoint location.
    A recommended breakpoint location is intended to “represent”
    a line, a statement and/or a semantically distinct subpart
    of a statement."

    (DWARF version 4 spec 6.2.2)

    So, non-statement line info also should be skipped.

    These can reduce unneeded probe points and also avoid an error.

    E.g. without this patch:

    # perf probe -a "clear_tasks_mm_cpumask:1"
    Added new events:
    probe:clear_tasks_mm_cpumask (on clear_tasks_mm_cpumask:1)
    probe:clear_tasks_mm_cpumask_1 (on clear_tasks_mm_cpumask:1)
    probe:clear_tasks_mm_cpumask_2 (on clear_tasks_mm_cpumask:1)
    probe:clear_tasks_mm_cpumask_3 (on clear_tasks_mm_cpumask:1)
    probe:clear_tasks_mm_cpumask_4 (on clear_tasks_mm_cpumask:1)

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

    perf record -e probe:clear_tasks_mm_cpumask_4 -aR sleep 1

    #

    This puts 5 probes on one line, but acutally it's not inlined function.
    This is because there are many non statement instructions at the
    function prologue.

    With this patch:

    # perf probe -a "clear_tasks_mm_cpumask:1"
    Added new event:
    probe:clear_tasks_mm_cpumask (on clear_tasks_mm_cpumask:1)

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

    perf record -e probe:clear_tasks_mm_cpumask -aR sleep 1

    #

    Now perf-probe skips unneeded addresses.

    Committer testing:

    Slightly different results, but similar:

    Before:

    # uname -a
    Linux quaco 5.3.8-200.fc30.x86_64 #1 SMP Tue Oct 29 14:46:22 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
    #
    # perf probe -a "clear_tasks_mm_cpumask:1"
    Added new events:
    probe:clear_tasks_mm_cpumask (on clear_tasks_mm_cpumask:1)
    probe:clear_tasks_mm_cpumask_1 (on clear_tasks_mm_cpumask:1)
    probe:clear_tasks_mm_cpumask_2 (on clear_tasks_mm_cpumask:1)

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

    perf record -e probe:clear_tasks_mm_cpumask_2 -aR sleep 1

    #

    After:

    # perf probe -a "clear_tasks_mm_cpumask:1"
    Added new event:
    probe:clear_tasks_mm_cpumask (on clear_tasks_mm_cpumask:1)

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

    perf record -e probe:clear_tasks_mm_cpumask -aR sleep 1

    # perf probe -l
    probe:clear_tasks_mm_cpumask (on clear_tasks_mm_cpumask@kernel/cpu.c)
    #

    Fixes: 4cc9cec636e7 ("perf probe: Introduce lines walker interface")
    Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
    Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Jiri Olsa <jolsa@redhat.com>
    Cc: Namhyung Kim <namhyung@kernel.org>
    Link: http://lore.kernel.org/lkml/157241936090.32002.12156347518596111660.stgit@devnote2
    Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    tools/perf/util/dwarf-aux.c | 7 +++++++
    1 file changed, 7 insertions(+)

    diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
    index 49f9c65f1a9c..d48bd5eaa0f2 100644
    --- a/tools/perf/util/dwarf-aux.c
    +++ b/tools/perf/util/dwarf-aux.c
    @@ -773,6 +773,7 @@ int die_walk_lines(Dwarf_Die *rt_die, line_walk_callback_t callback, void *data)
    int decl = 0, inl;
    Dwarf_Die die_mem, *cu_die;
    size_t nlines, i;
    + bool flag;

    /* Get the CU die */
    if (dwarf_tag(rt_die) != DW_TAG_compile_unit) {
    @@ -803,6 +804,12 @@ int die_walk_lines(Dwarf_Die *rt_die, line_walk_callback_t callback, void *data)
    "Possible error in debuginfo.\n");
    continue;
    }
    + /* Skip end-of-sequence */
    + if (dwarf_lineendsequence(line, &flag) != 0 || flag)
    + continue;
    + /* Skip Non statement line-info */
    + if (dwarf_linebeginstatement(line, &flag) != 0 || !flag)
    + continue;
    /* Filter lines based on address */
    if (rt_die != cu_die) {
    /*
    --
    2.20.1


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