On Jun 23, 2020, at 9:59 AM, Song Liu [off-list ref] wrote:

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On Jun 23, 2020, at 8:19 AM, Alexei Starovoitov [off-list ref] wrote:

On Tue, Jun 23, 2020 at 12:08 AM Song Liu [off-list ref] wrote:

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[...]

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+BPF_CALL_3(bpf_get_task_stack_trace, struct task_struct *, task,
+          void *, entries, u32, size)
+{
+       return stack_trace_save_tsk(task, (unsigned long *)entries, size, 0);
+}
+
+static int bpf_get_task_stack_trace_btf_ids[5];
+static const struct bpf_func_proto bpf_get_task_stack_trace_proto = {
+       .func           = bpf_get_task_stack_trace,
+       .gpl_only       = true,

why?

Actually, I am not sure when we should use gpl_only = true. 

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+       .ret_type       = RET_INTEGER,
+       .arg1_type      = ARG_PTR_TO_BTF_ID,
+       .arg2_type      = ARG_PTR_TO_MEM,
+       .arg3_type      = ARG_CONST_SIZE_OR_ZERO,

OR_ZERO ? why?

Will fix. 

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+       .btf_id         = bpf_get_task_stack_trace_btf_ids,
+};
+
static const struct bpf_func_proto *
raw_tp_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
{

@@ -1521,6 +1538,10 @@ tracing_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
              return prog->expected_attach_type == BPF_TRACE_ITER ?
                     &bpf_seq_write_proto :
                     NULL;
+       case BPF_FUNC_get_task_stack_trace:
+               return prog->expected_attach_type == BPF_TRACE_ITER ?
+                       &bpf_get_task_stack_trace_proto :

why limit to iter only?

I guess it is also useful for other types. Maybe move to bpf_tracing_func_proto()?

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+ *
+ * int bpf_get_task_stack_trace(struct task_struct *task, void *entries, u32 size)
+ *     Description
+ *             Save a task stack trace into array *entries*. This is a wrapper
+ *             over stack_trace_save_tsk().

size is not documented and looks wrong.
the verifier checks it in bytes, but it's consumed as number of u32s.

I am not 100% sure, but verifier seems check it correctly. And I think it is consumed
as u64s?

I was wrong. Verifier checks as bytes. Will fix. 

Song