[PATCH] rtla: Define _GNU_SOURCE in timerlat_bpf.c

[Tomas Glozar <tglozar@redhat.com>]

Newer versions of glibc include a definition of struct sched_attr in
bits/sched.h (included through sched.h which is included by rtla).
Commit 0eecee340672 ("tools/rtla: fix collision with glibc
sched_attr/sched_set_attr") has modified the definition of struct
sched_attr in utils.h, so that it is only applied with older versions of
glibc that do not define it, in order to prevent build failure.

The definition in bits/sched.h depends on _GNU_SOURCE.
timerlat_bpf.c does not define _GNU_SOURCE, making it fall back to the
definition in utils.h. The latter has two fields less, leading to
shifted offsets of struct timerlat_params in timerlat_bpf_init.

Because of the shift, timerlat_bpf_init incorrectly reads
params->entries as 0 for timerlat-hist and disables the creation of
histogram maps, causing breakage in BPF sample collection mode:

$ rtla timerlat hist -d 1s
Error pulling BPF data

Fix the issue by also defining _GNU_SOURCE in timerlat_bpf.c.

Fixes: e34293ddcebd ("rtla/timerlat: Add BPF skeleton to collect samples")
Signed-off-by: Tomas Glozar <tglozar@redhat.com>
---
 tools/tracing/rtla/src/timerlat_bpf.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/tracing/rtla/src/timerlat_bpf.c b/tools/tracing/rtla/src/timerlat_bpf.c
index 5abee884037a..0bc44ce5d69b 100644
--- a/tools/tracing/rtla/src/timerlat_bpf.c
+++ b/tools/tracing/rtla/src/timerlat_bpf.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #ifdef HAVE_BPF_SKEL
+#define _GNU_SOURCE
 #include "timerlat.h"
 #include "timerlat_bpf.h"
 #include "timerlat.skel.h"
-- 
2.49.0