[PATCH bpf-next v2 1/2] bpf: support access variable length array of integer type

From: Feng zhou
Date: Wed Apr 19 2023 - 23:28:35 EST


From: Feng Zhou <zhoufeng.zf@xxxxxxxxxxxxx>

After this commit:
bpf: Support variable length array in tracing programs (9c5f8a1008a1)
Trace programs can access variable length array, but for structure
type. This patch adds support for integer type.

Example:
Hook load_balance
struct sched_domain {
...
unsigned long span[];
}

The access: sd->span[0].

Co-developed-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Signed-off-by: Feng Zhou <zhoufeng.zf@xxxxxxxxxxxxx>
---
kernel/bpf/btf.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 027f9f8a3551..a0887ee44e89 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6157,11 +6157,13 @@ static int btf_struct_walk(struct bpf_verifier_log *log, const struct btf *btf,
if (off < moff)
goto error;

- /* Only allow structure for now, can be relaxed for
- * other types later.
- */
+ /* allow structure and integer */
t = btf_type_skip_modifiers(btf, array_elem->type,
NULL);
+
+ if (btf_type_is_int(t))
+ return WALK_SCALAR;
+
if (!btf_type_is_struct(t))
goto error;

--
2.20.1