linux-kernel - [PATCH] tool/perf: Perf build fails on 5.12.0rc2 on s390

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Date:   Tue,  9 Mar 2021 12:04:47 +0100
From:   Thomas Richter <tmricht@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        acme@...nel.org
Cc:     svens@...ux.ibm.com, gor@...ux.ibm.com, sumanthk@...ux.ibm.com,
        hca@...ux.ibm.com, Thomas Richter <tmricht@...ux.ibm.com>
Subject: [PATCH] tool/perf: Perf build fails on 5.12.0rc2 on s390

perf build fails on 5.12.0rc2 on s390 with this error message:

util/synthetic-events.c: In function
				‘__event__synthesize_thread.part.0.isra’:
util/synthetic-events.c:787:19: error: ‘kernel_thread’ may be
    used uninitialized in this function [-Werror=maybe-uninitialized]
    787 |   if (_pid == pid && !kernel_thread) {
        |       ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~

The build succeeds using command 'make DEBUG=y'.

The variable kernel_thread is set by this function sequence:

__event__synthesize_thread()
|    defines bool kernel_thread; as local variable and calls
+--> perf_event__prepare_comm(..., &kernel_thread)
     +--> perf_event__get_comm_ids(..., bool *kernel);
          On return of this function variable kernel is always
          set to true of false.

To prevent this compile error, assign variable kernel_thread
a value when it is defined.

Output after:
[root@...lp76 perf]# make  util/synthetic-events.o
....
 CC       util/synthetic-events.o
[root@...lp76 perf]#

Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
---
 tools/perf/util/synthetic-events.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
index b698046ec2db..5dd451695f33 100644
--- a/tools/perf/util/synthetic-events.c
+++ b/tools/perf/util/synthetic-events.c
@@ -758,7 +758,7 @@ static int __event__synthesize_thread(union perf_event *comm_event,
 	for (i = 0; i < n; i++) {
 		char *end;
 		pid_t _pid;
-		bool kernel_thread;
+		bool kernel_thread = false;
 
 		_pid = strtol(dirent[i]->d_name, &end, 10);
 		if (*end)
-- 
2.29.2