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Subject[PATCH AUTOSEL 4.14 095/130] 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 49f9c65f1a9c1..d48bd5eaa0f2a 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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