2022-04-16 02:04:26

by Alexander Lobakin

Subject: [PATCH bpf-next 10/11] samples: bpf: fix -Wsequence-point

In some libc implementations, CPU_SET() may utilize its first
argument several times. When combined with a post-increment, it
leads to:

samples/bpf/test_lru_dist.c:233:36: warning: operation on 'next_to_try' may be undefined [-Wsequence-point]
233 | CPU_SET(next_to_try++, &cpuset);
| ^

Split the sentence into two standalone operations to fix this.

Fixes: 5db58faf989f ("bpf: Add tests for the LRU bpf_htab")
Signed-off-by: Alexander Lobakin <[email protected]>
---
samples/bpf/test_lru_dist.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/samples/bpf/test_lru_dist.c b/samples/bpf/test_lru_dist.c
index be98ccb4952f..191643ec501e 100644
--- a/samples/bpf/test_lru_dist.c
+++ b/samples/bpf/test_lru_dist.c
@@ -229,7 +229,8 @@ static int sched_next_online(int pid, int next_to_try)

while (next_to_try < nr_cpus) {
CPU_ZERO(&cpuset);
- CPU_SET(next_to_try++, &cpuset);
+ CPU_SET(next_to_try, &cpuset);
+ next_to_try++;
if (!sched_setaffinity(pid, sizeof(cpuset), &cpuset))
break;
}
--
2.35.2

2022-04-16 02:17:02

by Song Liu

Subject: Re: [PATCH bpf-next 10/11] samples: bpf: fix -Wsequence-point

On Thu, Apr 14, 2022 at 3:47 PM Alexander Lobakin <[email protected]> wrote:
>
> In some libc implementations, CPU_SET() may utilize its first
> argument several times. When combined with a post-increment, it
> leads to:
>
> samples/bpf/test_lru_dist.c:233:36: warning: operation on 'next_to_try' may be undefined [-Wsequence-point]
> 233 | CPU_SET(next_to_try++, &cpuset);
> | ^
>
> Split the sentence into two standalone operations to fix this.
>
> Fixes: 5db58faf989f ("bpf: Add tests for the LRU bpf_htab")
> Signed-off-by: Alexander Lobakin <[email protected]>

Acked-by: Song Liu <[email protected]>

> ---
> samples/bpf/test_lru_dist.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/samples/bpf/test_lru_dist.c b/samples/bpf/test_lru_dist.c
> index be98ccb4952f..191643ec501e 100644
> --- a/samples/bpf/test_lru_dist.c
> +++ b/samples/bpf/test_lru_dist.c
> @@ -229,7 +229,8 @@ static int sched_next_online(int pid, int next_to_try)
>
> while (next_to_try < nr_cpus) {
> CPU_ZERO(&cpuset);
> - CPU_SET(next_to_try++, &cpuset);
> + CPU_SET(next_to_try, &cpuset);
> + next_to_try++;
> if (!sched_setaffinity(pid, sizeof(cpuset), &cpuset))
> break;
> }
> --
> 2.35.2
>
>