Re: [PATCH bpf v1] selftests/bpf: Fix error compiling cgroup_ancestor.c with musl libc

["Alexis Lothoré" <alexis.lothore@bootlin.com>]

Hello Tony,

On 10/9/24 01:12, Tony Ambardar wrote:
> Existing code calls connect() with a 'struct sockaddr_in6 *' argument
> where a 'struct sockaddr *' argument is declared, yielding compile errors
> when building for mips64el/musl-libc:
> 
> In file included from cgroup_ancestor.c:3:
> cgroup_ancestor.c: In function 'send_datagram':
> cgroup_ancestor.c:38:38: error: passing argument 2 of 'connect' from incompatible pointer type [-Werror=incompatible-pointer-types]
>    38 |         if (!ASSERT_OK(connect(sock, &addr, sizeof(addr)), "connect")) {
>       |                                      ^~~~~
>       |                                      |
>       |                                      struct sockaddr_in6 *
> ./test_progs.h:343:29: note: in definition of macro 'ASSERT_OK'
>   343 |         long long ___res = (res);                                       \
>       |                             ^~~
> In file included from .../netinet/in.h:10,
>                  from .../arpa/inet.h:9,
>                  from ./test_progs.h:17:
> .../sys/socket.h:386:19: note: expected 'const struct sockaddr *' but argument is of type 'struct sockaddr_in6 *'
>   386 | int connect (int, const struct sockaddr *, socklen_t);
>       |                   ^~~~~~~~~~~~~~~~~~~~~~~
> cc1: all warnings being treated as errors
> 
> This only compiles because of a glibc extension allowing declaration of the
> argument as a "transparent union" which includes both types above.
> 
> Explicitly cast the argument to allow compiling for both musl and glibc.

Thanks for the fix and the details :) Indeed it looks like all other tests
perform this cast on connect (either to (void *) or (struct sockaddr *)) to
prevent this issue, so that's a miss on my side when I rewrote this test.

> Cc: Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>
> Fixes: f957c230e173 ("selftests/bpf: convert test_skb_cgroup_id_user to test_progs")
> Signed-off-by: Tony Ambardar <tony.ambardar@gmail.com>

Reviewed-by: Alexis Lothoré <alexis.lothore@bootlin.com>

> ---
>  tools/testing/selftests/bpf/prog_tests/cgroup_ancestor.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_ancestor.c b/tools/testing/selftests/bpf/prog_tests/cgroup_ancestor.c
> index 9250a1e9f9af..3f9ffdf71343 100644
> --- a/tools/testing/selftests/bpf/prog_tests/cgroup_ancestor.c
> +++ b/tools/testing/selftests/bpf/prog_tests/cgroup_ancestor.c
> @@ -35,7 +35,7 @@ static int send_datagram(void)
>  	if (!ASSERT_OK_FD(sock, "create socket"))
>  		return sock;
>  
> -	if (!ASSERT_OK(connect(sock, &addr, sizeof(addr)), "connect")) {
> +	if (!ASSERT_OK(connect(sock, (struct sockaddr *)&addr, sizeof(addr)), "connect")) {
>  		close(sock);
>  		return -1;
>  	}


-- 
Alexis Lothoré, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com