[PATCH linux-next] perf parse-events: Fix big-endian 'overwrite' by writing correct union member

[Thomas Richter]

The "Read backward ring buffer" test crashes on big-endian (e.g. s390x)
due to a NULL dereference when the backward mmap path isn't enabled.

Reproducer:
  # ./perf test -F 'Read backward ring buffer'
  Segmentation fault (core dumped)
  # uname -m
  s390x
  #

Root cause:
get_config_terms() stores into evsel_config_term::val.val (u64) while later
code reads boolean fields such as evsel_config_term::val.overwrite.
On big-endian the 1-byte boolean is left-aligned, so writing
evsel_config_term::val.val = 1 is read back as
evsel_config_term::val.overwrite = 0,
leaving backward mmap disabled and a NULL map being used.

Store values in the union member that matches the term type, e.g.:
  /* for OVERWRITE */
  new_term->val.overwrite = 1;  /* not new_term->val.val = 1 */
to fix this.

Impact:
Enables backward mmap on big-endian and prevents the crash.
No change on little-endian.

Output after:
 # ./perf test -Fv 44
 --- start ---
 Using CPUID IBM,9175,705,ME1,3.8,002f
 mmap size 1052672B
 mmap size 8192B
 ---- end ----
 44: Read backward ring buffer                         : Ok
 #

Fixes: 159ca97cd97c ("perf parse-events: Refactor get_config_terms() to remove macros")
Signed-off-by: Thomas Richter <tmricht@xxxxxxxxxxxxx>
Reviewed-by: Jan Polensky <japo@xxxxxxxxxxxxx>
Cc: James Clark <james.clark@xxxxxxxxxx>
Cc: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/util/parse-events.c | 49 +++++++++++++++++++++++++++++++++-
 1 file changed, 48 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index d4647ded340f..12fe5392c832 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -1250,7 +1250,54 @@ static int get_config_terms(const struct parse_events_terms *head_config,
 			}
 			new_term->free_str = true;
 		} else {
-			new_term->val.val = val;
+			switch (new_type) {
+			case EVSEL__CONFIG_TERM_PERIOD:
+				new_term->val.period = val;
+				break;
+			case EVSEL__CONFIG_TERM_FREQ:
+				new_term->val.freq = val;
+				break;
+			case EVSEL__CONFIG_TERM_TIME:
+				new_term->val.time = val;
+				break;
+			case EVSEL__CONFIG_TERM_STACK_USER:
+				new_term->val.stack_user = val;
+				break;
+			case EVSEL__CONFIG_TERM_INHERIT:
+				new_term->val.inherit = val;
+				break;
+			case EVSEL__CONFIG_TERM_OVERWRITE:
+				new_term->val.overwrite = val;
+				break;
+			case EVSEL__CONFIG_TERM_MAX_STACK:
+				new_term->val.max_stack = val;
+				break;
+			case EVSEL__CONFIG_TERM_MAX_EVENTS:
+				new_term->val.max_events = val;
+				break;
+			case EVSEL__CONFIG_TERM_PERCORE:
+				new_term->val.percore = val;
+				break;
+			case EVSEL__CONFIG_TERM_AUX_OUTPUT:
+				new_term->val.aux_output = val;
+				break;
+			case EVSEL__CONFIG_TERM_AUX_SAMPLE_SIZE:
+				new_term->val.aux_sample_size = val;
+				break;
+			case EVSEL__CONFIG_TERM_CALLGRAPH:
+			case EVSEL__CONFIG_TERM_DRV_CFG:
+			case EVSEL__CONFIG_TERM_BRANCH:
+			case EVSEL__CONFIG_TERM_AUX_ACTION:
+			case EVSEL__CONFIG_TERM_USR_CHG_CONFIG:
+			case EVSEL__CONFIG_TERM_USR_CHG_CONFIG1:
+			case EVSEL__CONFIG_TERM_USR_CHG_CONFIG2:
+			case EVSEL__CONFIG_TERM_USR_CHG_CONFIG3:
+			case EVSEL__CONFIG_TERM_USR_CHG_CONFIG4:
+			case EVSEL__CONFIG_TERM_RATIO_TO_PREV:
+			default:
+				new_term->val.val = val;
+				break;
+			}
 		}
 	}
 	return 0;
-- 
2.53.0