Thanks for taking a look!

On Fri, Aug 21, 2020 at 8:30 PM Andrii Nakryiko
[off-list ref] wrote:

On Wed, Aug 19, 2020 at 3:42 PM Hao Luo [off-list ref] wrote:

quoted

Test bpf_per_cpu_ptr(). Test two paths in the kernel. If the base
pointer points to a struct, the returned reg is of type PTR_TO_BTF_ID.
Direct pointer dereference can be applied on the returned variable.
If the base pointer isn't a struct, the returned reg is of type
PTR_TO_MEM, which also supports direct pointer dereference.

Signed-off-by: Hao Luo <redacted>
---

Acked-by: Andrii Nakryiko <redacted>

[...]

quoted

 __u64 out__runqueues = -1;
 __u64 out__bpf_prog_active = -1;
+__u32 out__rq_cpu = -1;
+unsigned long out__process_counts = -1;

try to not use long for variables, it is 32-bit integer in user-space
but always 64-bit in BPF. This causes problems when using skeleton on
32-bit architecture.

Ack. I will use another variable of type 'int' instead.

quoted

-extern const struct rq runqueues __ksym; /* struct type global var. */
+extern const struct rq runqueues __ksym; /* struct type percpu var. */
 extern const int bpf_prog_active __ksym; /* int type global var. */
+extern const unsigned long process_counts __ksym; /* int type percpu var. */

 SEC("raw_tp/sys_enter")
 int handler(const void *ctx)
 {
+       struct rq *rq;
+       unsigned long *count;
+
        out__runqueues = (__u64)&runqueues;
        out__bpf_prog_active = (__u64)&bpf_prog_active;

+       rq = (struct rq *)bpf_per_cpu_ptr(&runqueues, 1);
+       if (rq)
+               out__rq_cpu = rq->cpu;

this is awesome!

Are there any per-cpu variables that are arrays? Would be nice to test
those too.

There are currently per-cpu arrays, but not common. There is a
'pmc_prev_left' in arch/x86, I can add that in this test.

[...]