On Tue, Oct 3, 2017 at 9:26 PM, zhiting zhu via iovisor-dev
<iovisor-dev@...> wrote:
> Hi,
>
> What's the use case for backward jump of ebpf? The verifier will reject the
> backward edge which makes the backward jump not useful. Am I missing
> something?
>
> Also, from what I read online, some slides said ebpf allows backward jump
> and some said doesn't. From the bytecode, it seems it allows it. I want some
> classification here. Thanks!

There is no such thing as 'backward edge'.
In graph theory there is 'back edge' which is the same as saying
there is a loop in control flow graph.
The kernel verifier has logic to detect back edges and reject such programs.
Backwards jumps are allowed, since backward jump != loop.