linux-kernel - [PATCH 5.8 26/99] libbpf: Fix build failure from uninitialized variable warning

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Message-Id: <20200929105931.016376299@linuxfoundation.org>
Date:   Tue, 29 Sep 2020 13:01:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Tony Ambardar <Tony.Ambardar@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.8 26/99] libbpf: Fix build failure from uninitialized variable warning

From: Tony Ambardar <tony.ambardar@...il.com>

[ Upstream commit 3168c158ad3535af1cd7423c9f8cd5ac549f2f9c ]

While compiling libbpf, some GCC versions (at least 8.4.0) have difficulty
determining control flow and a emit warning for potentially uninitialized
usage of 'map', which results in a build error if using "-Werror":

In file included from libbpf.c:56:
libbpf.c: In function '__bpf_object__open':
libbpf_internal.h:59:2: warning: 'map' may be used uninitialized in this function [-Wmaybe-uninitialized]
  libbpf_print(level, "libbpf: " fmt, ##__VA_ARGS__); \
  ^~~~~~~~~~~~
libbpf.c:5032:18: note: 'map' was declared here
  struct bpf_map *map, *targ_map;
                  ^~~

The warning/error is false based on code inspection, so silence it with a
NULL initialization.

Fixes: 646f02ffdd49 ("libbpf: Add BTF-defined map-in-map support")
Reference: 063e68813391 ("libbpf: Fix false uninitialized variable warning")
Signed-off-by: Tony Ambardar <Tony.Ambardar@...il.com>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Link: https://lore.kernel.org/bpf/20200831000304.1696435-1-Tony.Ambardar@gmail.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 tools/lib/bpf/libbpf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 3ac0094706b81..236c91aff48f8 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -5030,8 +5030,8 @@ static int bpf_object__collect_map_relos(struct bpf_object *obj,
 	int i, j, nrels, new_sz;
 	const struct btf_var_secinfo *vi = NULL;
 	const struct btf_type *sec, *var, *def;
+	struct bpf_map *map = NULL, *targ_map;
 	const struct btf_member *member;
-	struct bpf_map *map, *targ_map;
 	const char *name, *mname;
 	Elf_Data *symbols;
 	unsigned int moff;
-- 
2.25.1