2020-04-04 05:16:23

by Jeremy Cline

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

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 <[email protected]>
---
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

2020-04-06 02:47:32

by Andrii Nakryiko

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

On Fri, Apr 3, 2020 at 10:15 PM Jeremy Cline <[email protected]> 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 <[email protected]>
> ---

Yep, unfortunately compiler is not that smart.

Acked-by: Andrii Nakryiko <[email protected]>

> 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
>

2020-04-06 20:16:01

by Daniel Borkmann

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

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 <[email protected]>

Applied, thanks!