linux-kernel - [PATCH v2] perf: Skip and warn on unknown format 'configN' attrs

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Date:   Fri,  9 Sep 2022 15:45:09 -0500
From:   Rob Herring <robh@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>
Cc:     James Clark <james.clark@....com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] perf: Skip and warn on unknown format 'configN' attrs

If the kernel exposes a new perf_event_attr field in a format attr, perf
will return an error stating the specified PMU can't be found. For
example, a format attr with 'config3:0-63' causes an error as config3 is
unknown to perf. This causes a compatibility issue between a newer
kernel with older perf tool.

Before this change with a kernel adding 'config3' I get:

$ perf record -e arm_spe// -- true
event syntax error: 'arm_spe//'
                     \___ Cannot find PMU `arm_spe'. Missing kernel support?
Run 'perf list' for a list of valid events

 Usage: perf record [<options>] [<command>]
    or: perf record [<options>] -- <command> [<options>]

    -e, --event <event>   event selector. use 'perf list' to list
available events

After this change, I get:

$ perf record -e arm_spe// -- true
WARNING: format 'inv_event_filter' requires 'config3' which is not supported by this version of perf!
[ perf record: Woken up 2 times to write data ]
[ perf record: Captured and wrote 0.091 MB perf.data ]

To support unknown configN formats, rework the YACC implementation to
pass any config[0-9]+ format to perf_pmu__new_format() to handle with a
warning.

Note that the user will get the warning if *any* PMU has an unsupported
format attr even if that PMU isn't used. This is because perf tool scans
all the PMUs.

Signed-off-by: Rob Herring <robh@...nel.org>
---
v2:
 - Rework YACC code to handle configN formats in C code
 - Add a warning when an unknown configN attr is found

v1: https://lore.kernel.org/all/20220901184709.2179309-1-robh@kernel.org/
---
 tools/perf/util/pmu.c |  6 ++++++
 tools/perf/util/pmu.l |  2 --
 tools/perf/util/pmu.y | 15 ++++-----------
 3 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index 89655d53117a..6757db7d559c 100644
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -1475,6 +1475,12 @@ int perf_pmu__new_format(struct list_head *list, char *name,
 {
 	struct perf_pmu_format *format;
 
+	if (config > PERF_PMU_FORMAT_VALUE_CONFIG2) {
+		pr_warning("WARNING: format '%s' requires 'config%d' which is not supported by this version of perf!\n",
+			   name, config);
+		return 0;
+	}
+
 	format = zalloc(sizeof(*format));
 	if (!format)
 		return -ENOMEM;
diff --git a/tools/perf/util/pmu.l b/tools/perf/util/pmu.l
index a15d9fbd7c0e..58b4926cfaca 100644
--- a/tools/perf/util/pmu.l
+++ b/tools/perf/util/pmu.l
@@ -27,8 +27,6 @@ num_dec         [0-9]+
 
 {num_dec}	{ return value(10); }
 config		{ return PP_CONFIG; }
-config1		{ return PP_CONFIG1; }
-config2		{ return PP_CONFIG2; }
 -		{ return '-'; }
 :		{ return ':'; }
 ,		{ return ','; }
diff --git a/tools/perf/util/pmu.y b/tools/perf/util/pmu.y
index bfd7e8509869..283efe059819 100644
--- a/tools/perf/util/pmu.y
+++ b/tools/perf/util/pmu.y
@@ -20,7 +20,7 @@ do { \
 
 %}
 
-%token PP_CONFIG PP_CONFIG1 PP_CONFIG2
+%token PP_CONFIG
 %token PP_VALUE PP_ERROR
 %type <num> PP_VALUE
 %type <bits> bit_term
@@ -47,18 +47,11 @@ PP_CONFIG ':' bits
 				      $3));
 }
 |
-PP_CONFIG1 ':' bits
+PP_CONFIG PP_VALUE ':' bits
 {
 	ABORT_ON(perf_pmu__new_format(format, name,
-				      PERF_PMU_FORMAT_VALUE_CONFIG1,
-				      $3));
-}
-|
-PP_CONFIG2 ':' bits
-{
-	ABORT_ON(perf_pmu__new_format(format, name,
-				      PERF_PMU_FORMAT_VALUE_CONFIG2,
-				      $3));
+				      $2,
+				      $4));
 }
 
 bits:
-- 
2.34.1