netdev - [PATCH bpf-next] libbpf: make LIBBPF_OPTS macro strictly a variable declaration

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Date:   Mon, 21 Oct 2019 09:57:44 -0700
From:   Andrii Nakryiko <andriin@...com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>
CC:     <andrii.nakryiko@...il.com>, <kernel-team@...com>,
        Andrii Nakryiko <andriin@...com>
Subject: [PATCH bpf-next] libbpf: make LIBBPF_OPTS macro strictly a variable declaration

LIBBPF_OPTS is implemented as a mix of field declaration and memset
+ assignment. This makes it neither variable declaration nor purely
statements, which is a problem, because you can't mix it with either
other variable declarations nor other function statements, because C90
compiler mode emits warning on mixing all that together.

This patch changes LIBBPF_OPTS into a strictly declaration of variable
and solves this problem, as can be seen in case of bpftool, which
previously would emit compiler warning, if done this way (LIBBPF_OPTS as
part of function variables declaration block).

Signed-off-by: Andrii Nakryiko <andriin@...com>
---
 tools/bpf/bpftool/prog.c |  6 +++---
 tools/lib/bpf/libbpf.h   | 13 +++++++------
 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index 27da96a797ab..1a7e8ddf8232 100644
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -1093,6 +1093,9 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
 {
 	struct bpf_object_load_attr load_attr = { 0 };
 	enum bpf_prog_type common_prog_type = BPF_PROG_TYPE_UNSPEC;
+	LIBBPF_OPTS(bpf_object_open_opts, open_opts,
+		.relaxed_maps = relaxed_maps,
+	);
 	enum bpf_attach_type expected_attach_type;
 	struct map_replace *map_replace = NULL;
 	struct bpf_program *prog = NULL, *pos;
@@ -1106,9 +1109,6 @@ static int load_with_options(int argc, char **argv, bool first_prog_only)
 	const char *file;
 	int idx, err;
 
-	LIBBPF_OPTS(bpf_object_open_opts, open_opts,
-		.relaxed_maps = relaxed_maps,
-	);
 
 	if (!REQ_ARGS(2))
 		return -1;
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 0fdf086beba7..bf105e9e866f 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -77,12 +77,13 @@ struct bpf_object_open_attr {
  * bytes, but that's the best way I've found and it seems to work in practice.
  */
 #define LIBBPF_OPTS(TYPE, NAME, ...)					    \
-	struct TYPE NAME;						    \
-	memset(&NAME, 0, sizeof(struct TYPE));				    \
-	NAME = (struct TYPE) {						    \
-		.sz = sizeof(struct TYPE),				    \
-		__VA_ARGS__						    \
-	}
+	struct TYPE NAME = ({ 						    \
+		memset(&NAME, 0, sizeof(struct TYPE));			    \
+		(struct TYPE) {						    \
+			.sz = sizeof(struct TYPE),			    \
+			__VA_ARGS__					    \
+		};							    \
+	})
 
 struct bpf_object_open_opts {
 	/* size of this struct, for forward/backward compatiblity */
-- 
2.17.1