Re: [PATCH] libbpf: fix warnings "'pad_type' 'pad_bits' 'new_off' may be used uninitialized"

[Jiri Olsa <olsajiri@gmail.com>]

On Thu, Jul 27, 2023 at 04:25:36PM +0800, Xiangyu Chen wrote:
> From: Xiangyu Chen <xiangyu.chen@windriver.com>
> 
> When turn on the yocto DEBUG_BUILD flag, the build options for gcc would enable maybe-uninitialized,
> and following warnings would be reported as below:

curious, what's the gcc version? I can't reproduce that,
and we already have all warnings enabled:

  CFLAGS += -Werror -Wall

they seem like false warnings also, because ARRAY_SIZE(pads)
will be always > 0

jirka

> 
> | btf_dump.c: In function 'btf_dump_emit_bit_padding':
> | btf_dump.c:916:4: error: 'pad_type' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> |   916 |    btf_dump_printf(d, "\n%s%s: %d;", pfx(lvl), pad_type,
> |       |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> |   917 |      in_bitfield ? new_off - cur_off : 0);
> |       |      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> | btf_dump.c:929:6: error: 'pad_bits' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> |   929 |   if (bits == pad_bits) {
> |       |      ^
> | btf_dump.c:913:28: error: 'new_off' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> |   913 |       (new_off == next_off && roundup(cur_off, next_align * 8) != new_off) ||
> |       |       ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> |   HOSTLD  scripts/mod/modpost
> 
> Signed-off-by: Xiangyu Chen <xiangyu.chen@windriver.com>
> ---
>  tools/lib/bpf/btf_dump.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
> index 4d9f30bf7f01..79923c3b8777 100644
> --- a/tools/lib/bpf/btf_dump.c
> +++ b/tools/lib/bpf/btf_dump.c
> @@ -867,8 +867,8 @@ static void btf_dump_emit_bit_padding(const struct btf_dump *d,
>  	} pads[] = {
>  		{"long", d->ptr_sz * 8}, {"int", 32}, {"short", 16}, {"char", 8}
>  	};
> -	int new_off, pad_bits, bits, i;
> -	const char *pad_type;
> +	int new_off = 0, pad_bits = 0, bits, i;
> +	const char *pad_type = NULL;
>  
>  	if (cur_off >= next_off)
>  		return; /* no gap */
> -- 
> 2.34.1
> 
>