[PATCH 2/2] bpf: Fix warning of incorrect type in return expression

[PATCH 2/2] bpf: Fix warning of incorrect type in return expression

[Jules Irenge]

Sparse reports a warning at bpf_array_map_seq_start()

"warning: incorrect type in return expression (different address spaces)"

The root cause is the function expect a return of type void *
but instead got a percpu value in one of the return.

To fix this a variable of type void * is created
and the complainining return value is saved into the variable and return.

Fix incorrect type in return expression

Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
---
 kernel/bpf/arraymap.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 624527401d4d..b1914168c23a 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -548,6 +548,7 @@ static void *bpf_array_map_seq_start(struct seq_file *seq, loff_t *pos)
 	struct bpf_map *map = info->map;
 	struct bpf_array *array;
 	u32 index;
+	void *pptrs;
 
 	if (info->index >= map->max_entries)
 		return NULL;
@@ -556,8 +557,10 @@ static void *bpf_array_map_seq_start(struct seq_file *seq, loff_t *pos)
 		++*pos;
 	array = container_of(map, struct bpf_array, map);
 	index = info->index & array->index_mask;
-	if (info->percpu_value_buf)
-	       return array->pptrs[index];
+	if (info->percpu_value_buf) {
+		pptrs = &array->pptrs[index];
+		return pptrs;
+	}
 	return array_map_elem_ptr(array, index);
 }
 
-- 
2.35.1

Re: [PATCH 2/2] bpf: Fix warning of incorrect type in return expression

[Alexei Starovoitov]

On Sat, Sep 3, 2022 at 12:02 PM Jules Irenge <jbi.octave@gmail.com> wrote:
>
> Sparse reports a warning at bpf_array_map_seq_start()
>
> "warning: incorrect type in return expression (different address spaces)"
>
> The root cause is the function expect a return of type void *
> but instead got a percpu value in one of the return.
>
> To fix this a variable of type void * is created
> and the complainining return value is saved into the variable and return.
>
> Fix incorrect type in return expression
>
> Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
> ---
>  kernel/bpf/arraymap.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> index 624527401d4d..b1914168c23a 100644
> --- a/kernel/bpf/arraymap.c
> +++ b/kernel/bpf/arraymap.c
> @@ -548,6 +548,7 @@ static void *bpf_array_map_seq_start(struct seq_file *seq, loff_t *pos)
>         struct bpf_map *map = info->map;
>         struct bpf_array *array;
>         u32 index;
> +       void *pptrs;
>
>         if (info->index >= map->max_entries)
>                 return NULL;
> @@ -556,8 +557,10 @@ static void *bpf_array_map_seq_start(struct seq_file *seq, loff_t *pos)
>                 ++*pos;
>         array = container_of(map, struct bpf_array, map);
>         index = info->index & array->index_mask;
> -       if (info->percpu_value_buf)
> -              return array->pptrs[index];
> +       if (info->percpu_value_buf) {
> +               pptrs = &array->pptrs[index];
> +               return pptrs;
> +       }

Somebody will surely send a patch to optimize above back
to original code.
Please find a different way to shut up sparse or just ignore it.