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

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Message-ID: <c70aa238-fcc0-4fa9-2ec3-8e8d3aea478b@fb.com>
Date:   Thu, 11 Apr 2019 04:20:20 +0000
From:   Yonghong Song <yhs@...com>
To:     Andrey Ignatov <rdna@...com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next] libbpf: Fix build with gcc-8



On 4/10/19 6:36 PM, Andrey Ignatov wrote:
> 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>

Acked-by: Yonghong Song <yhs@...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;
>