linux-kernel - Re: [PATCH bpf-next] selftests/bpf: Fix strncpy() fortify warning

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Date:   Tue, 1 Nov 2022 14:56:23 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Rong Tao <rtoax@...mail.com>, david.laight@...lab.com
Cc:     andrii.nakryiko@...il.com, andrii@...nel.org, ast@...nel.org,
        bpf@...r.kernel.org, haoluo@...gle.com, john.fastabend@...il.com,
        jolsa@...nel.org, kpsingh@...nel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, martin.lau@...ux.dev,
        mykolal@...com, rongtao@...tc.cn, sdf@...gle.com, shuah@...nel.org,
        song@...nel.org, yhs@...com
Subject: Re: [PATCH bpf-next] selftests/bpf: Fix strncpy() fortify warning

On 11/1/22 1:21 PM, Rong Tao wrote:
> From: Rong Tao <rongtao@...tc.cn>
> 
> move libbpf_strlcpy() to bpf_util.h, and replace strncpy() with
> libbpf_strlcpy(), fix compile warning.
> 
> Compile samples/bpf, warning:
> $ cd samples/bpf
> $ make
> ...
> cgroup_helpers.c: In function ‘__enable_controllers’:
> cgroup_helpers.c:80:17: warning: ‘strncpy’ specified bound 4097 equals destination size [-Wstringop-truncation]
>     80 |                 strncpy(enable, controllers, sizeof(enable));
>        |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 

BPF CI now throws a new warning after your patch:

https://github.com/kernel-patches/bpf/actions/runs/3369416153/jobs/5589052613

   [...]
   xsk.c:536:2: error: call to undeclared function 'libbpf_strlcpy'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
           libbpf_strlcpy(ifr.ifr_name, ctx->ifname, IFNAMSIZ);
           ^
   xsk.c:755:2: error: call to undeclared function 'libbpf_strlcpy'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
           libbpf_strlcpy(ctx->ifname, ifname, IFNAMSIZ);
           ^
   xsk.c:942:2: error: call to undeclared function 'libbpf_strlcpy'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
           libbpf_strlcpy(ctx->ifname, ifname, IFNAMSIZ);
           ^
   3 errors generated.
   make: *** [Makefile:166: /tmp/work/bpf/bpf/tools/testing/selftests/bpf/xsk.o] Error 1
   make: *** Waiting for unfinished jobs....