netdev - [PATCH bpf-next] libbpf: Fix build with gcc-8

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Date:   Wed, 10 Apr 2019 18:36:43 -0700
From:   Andrey Ignatov <rdna@...com>
To:     <netdev@...r.kernel.org>
CC:     Andrey Ignatov <rdna@...com>, <ast@...nel.org>,
        <daniel@...earbox.net>, <kernel-team@...com>
Subject: [PATCH bpf-next] libbpf: Fix build with gcc-8

Reported in [1].

With gcc 8.3.0 the following error is issued:

  cc -Ibpf@sta -I. -I.. -I.././include -I.././include/uapi
  -fdiagnostics-color=always -fsanitize=address,undefined -fno-omit-frame-pointer
  -pipe -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Werror -g -fPIC -g -O2
  -Werror -Wall -Wno-pointer-arith -Wno-sign-compare  -MD -MQ
  'bpf@.../src_libbpf.c.o' -MF 'bpf@.../src_libbpf.c.o.d' -o
  'bpf@.../src_libbpf.c.o' -c ../src/libbpf.c
  ../src/libbpf.c: In function 'bpf_object__elf_collect':
  ../src/libbpf.c:947:18: error: 'map_def_sz' may be used uninitialized in this
  function [-Werror=maybe-uninitialized]
     if (map_def_sz <= sizeof(struct bpf_map_def)) {
         ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ../src/libbpf.c:827:18: note: 'map_def_sz' was declared here
    int i, map_idx, map_def_sz, nr_syms, nr_maps = 0, nr_maps_glob = 0;
                    ^~~~~~~~~~

According to [2] -Wmaybe-uninitialized is enabled by -Wall.
Same error is generated by clang's -Wconditional-uninitialized.

[1] https://github.com/libbpf/libbpf/pull/29#issuecomment-481902601
[2] https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

Fixes: d859900c4c56 ("bpf, libbpf: support global data/bss/rodata sections")
Reported-by: Evgeny Vereshchagin <evvers@...ru>
Signed-off-by: Andrey Ignatov <rdna@...com>
---
 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 e2a457e7c318..67484cf32b2e 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -824,7 +824,7 @@ bpf_object__init_internal_map(struct bpf_object *obj, struct bpf_map *map,
 static int
 bpf_object__init_maps(struct bpf_object *obj, int flags)
 {
-	int i, map_idx, map_def_sz, nr_syms, nr_maps = 0, nr_maps_glob = 0;
+	int i, map_idx, map_def_sz = 0, nr_syms, nr_maps = 0, nr_maps_glob = 0;
 	bool strict = !(flags & MAPS_RELAX_COMPAT);
 	Elf_Data *symbols = obj->efile.symbols;
 	Elf_Data *data = NULL;
-- 
2.17.1