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From:   Yosry Ahmed <yosryahmed@google.com>
Date:   Fri, 20 May 2022 09:06:45 -0700
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Subject: Re: [PATCH bpf-next v1 2/5] cgroup: bpf: add cgroup_rstat_updated()
 and cgroup_rstat_flush() kfuncs
To:     Tejun Heo <tj@kernel.org>
Cc:     Kumar Kartikeya Dwivedi <memxor@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
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On Fri, May 20, 2022 at 4:16 AM Tejun Heo <tj@kernel.org> wrote:
>
> On Fri, May 20, 2022 at 03:06:07PM +0530, Kumar Kartikeya Dwivedi wrote:
> > With static noinline, the compiler will optimize away the function. With global
> > noinline, it can still optimize away the call site, but will keep the function
> > definition, so attach works. Therefore __weak is needed to ensure call is still
> > emitted. With GCC __attribute__((noipa)) might have been more appropritate, but
> > LLVM doesn't support it, so __weak is the next best thing supported by both with
> > the same side effect.

Thanks a lot for the explanation!

>
> Ah, okay, so it's to prevent compiler from optimizing away call to a noop
> function by telling it that we don't know what the function might eventually
> be. Thanks for the explanation. Yosry, can you please add a comment
> explaining what's going on?

Will add a comment explaining things in the next section.  Thanks for
reviewing this, Tejun!

>
> Thanks.
>
> --
> tejun