[PATCH] libbpf: Initialize *nl_pid so gcc 10 is happy

[PATCH] libbpf: Initialize *nl_pid so gcc 10 is happy

[Jeremy Cline]

Builds of Fedora's kernel-tools package started to fail with "may be
used uninitialized" warnings for nl_pid in bpf_set_link_xdp_fd() and
bpf_get_link_xdp_info() on the s390 architecture.

Although libbpf_netlink_open() always returns a negative number when it
does not set *nl_pid, the compiler does not determine this and thus
believes the variable might be used uninitialized. Assuage gcc's fears
by explicitly initializing nl_pid.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1807781
Signed-off-by: Jeremy Cline <jcline@redhat.com>
---
 tools/lib/bpf/netlink.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c
index 18b5319025e19..9a14694176de0 100644
--- a/tools/lib/bpf/netlink.c
+++ b/tools/lib/bpf/netlink.c
@@ -142,7 +142,7 @@ static int __bpf_set_link_xdp_fd_replace(int ifindex, int fd, int old_fd,
 		struct ifinfomsg ifinfo;
 		char             attrbuf[64];
 	} req;
-	__u32 nl_pid;
+	__u32 nl_pid = 0;
 
 	sock = libbpf_netlink_open(&nl_pid);
 	if (sock < 0)
@@ -288,7 +288,7 @@ int bpf_get_link_xdp_info(int ifindex, struct xdp_link_info *info,
 {
 	struct xdp_id_md xdp_id = {};
 	int sock, ret;
-	__u32 nl_pid;
+	__u32 nl_pid = 0;
 	__u32 mask;
 
 	if (flags & ~XDP_FLAGS_MASK || !info_size)
-- 
2.26.0

Re: [PATCH] libbpf: Initialize *nl_pid so gcc 10 is happy

[Andrii Nakryiko]

On Fri, Apr 3, 2020 at 10:15 PM Jeremy Cline <jcline@redhat.com> wrote:
>
> Builds of Fedora's kernel-tools package started to fail with "may be
> used uninitialized" warnings for nl_pid in bpf_set_link_xdp_fd() and
> bpf_get_link_xdp_info() on the s390 architecture.
>
> Although libbpf_netlink_open() always returns a negative number when it
> does not set *nl_pid, the compiler does not determine this and thus
> believes the variable might be used uninitialized. Assuage gcc's fears
> by explicitly initializing nl_pid.
>
> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1807781
> Signed-off-by: Jeremy Cline <jcline@redhat.com>
> ---

Yep, unfortunately compiler is not that smart.

Acked-by: Andrii Nakryiko <andriin@fb.com>

>  tools/lib/bpf/netlink.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c
> index 18b5319025e19..9a14694176de0 100644
> --- a/tools/lib/bpf/netlink.c
> +++ b/tools/lib/bpf/netlink.c
> @@ -142,7 +142,7 @@ static int __bpf_set_link_xdp_fd_replace(int ifindex, int fd, int old_fd,
>                 struct ifinfomsg ifinfo;
>                 char             attrbuf[64];
>         } req;
> -       __u32 nl_pid;
> +       __u32 nl_pid = 0;
>
>         sock = libbpf_netlink_open(&nl_pid);
>         if (sock < 0)
> @@ -288,7 +288,7 @@ int bpf_get_link_xdp_info(int ifindex, struct xdp_link_info *info,
>  {
>         struct xdp_id_md xdp_id = {};
>         int sock, ret;
> -       __u32 nl_pid;
> +       __u32 nl_pid = 0;
>         __u32 mask;
>
>         if (flags & ~XDP_FLAGS_MASK || !info_size)
> --
> 2.26.0
>

Re: [PATCH] libbpf: Initialize *nl_pid so gcc 10 is happy

[Daniel Borkmann]

On 4/4/20 7:14 AM, Jeremy Cline wrote:
> Builds of Fedora's kernel-tools package started to fail with "may be
> used uninitialized" warnings for nl_pid in bpf_set_link_xdp_fd() and
> bpf_get_link_xdp_info() on the s390 architecture.
> 
> Although libbpf_netlink_open() always returns a negative number when it
> does not set *nl_pid, the compiler does not determine this and thus
> believes the variable might be used uninitialized. Assuage gcc's fears
> by explicitly initializing nl_pid.
> 
> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1807781
> Signed-off-by: Jeremy Cline <jcline@redhat.com>

Applied, thanks!