[PATCH 4.19 145/243] tools/bpf: make libbpf _GNU_SOURCE friendly

[Greg Kroah-Hartman]

From: Yonghong Song <yhs@xxxxxx>

[ Upstream commit b42699547fc9fb1057795bccc21a6445743a7fde ]

During porting libbpf to bcc, I got some warnings like below:
  ...
  [  2%] Building C object src/cc/CMakeFiles/bpf-shared.dir/libbpf/src/libbpf.c.o
  /home/yhs/work/bcc2/src/cc/libbpf/src/libbpf.c:12:0:
  warning: "_GNU_SOURCE" redefined [enabled by default]
   #define _GNU_SOURCE
  ...
  [  3%] Building C object src/cc/CMakeFiles/bpf-shared.dir/libbpf/src/libbpf_errno.c.o
  /home/yhs/work/bcc2/src/cc/libbpf/src/libbpf_errno.c: In function âlibbpf_strerrorâ:
  /home/yhs/work/bcc2/src/cc/libbpf/src/libbpf_errno.c:45:7:
  warning: assignment makes integer from pointer without a cast [enabled by default]
     ret = strerror_r(err, buf, size);
  ...

bcc is built with _GNU_SOURCE defined and this caused the above warning.
This patch intends to make libpf _GNU_SOURCE friendly by
  . define _GNU_SOURCE in libbpf.c unless it is not defined
  . undefine _GNU_SOURCE as non-gnu version of strerror_r is expected.

Signed-off-by: Yonghong Song <yhs@xxxxxx>
Acked-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 tools/lib/bpf/libbpf.c       | 2 ++
 tools/lib/bpf/libbpf_errno.c | 1 +
 2 files changed, 3 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index a350f97e3a1a4..a62be78fc07b1 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -22,7 +22,9 @@
  * License along with this program; if not,  see <http://www.gnu.org/licenses>
  */
 
+#ifndef _GNU_SOURCE
 #define _GNU_SOURCE
+#endif
 #include <stdlib.h>
 #include <stdio.h>
 #include <stdarg.h>
diff --git a/tools/lib/bpf/libbpf_errno.c b/tools/lib/bpf/libbpf_errno.c
index d9ba851bd7f9f..d2d17226d9d6b 100644
--- a/tools/lib/bpf/libbpf_errno.c
+++ b/tools/lib/bpf/libbpf_errno.c
@@ -20,6 +20,7 @@
  * License along with this program; if not,  see <http://www.gnu.org/licenses>
  */
 
+#undef _GNU_SOURCE
 #include <stdio.h>
 #include <string.h>
 
-- 
2.20.1