linux-kernel - Re: [PATCH v2] arm: eBPF JIT compiler

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Message-ID: <CAHgaXdKGJFh8jO44gwCqe0cijoztf39bK9k8ioBtYDjzb4vvZw@mail.gmail.com>
Date:   Wed, 21 Jun 2017 19:56:34 +0530
From:   Shubham Bansal <illusionist.neo@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Kees Cook <keescook@...omium.org>,
        Network Development <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>, Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH v2] arm: eBPF JIT compiler

Hi Daniel,

>
> So my question would be, why can't the JIT imitate something
> similar to what we do in the interpreter as well? So looking
> at the disasm of what gcc compiles for the interpreter when it's
> doing the above call could help as well in going forward. Not
> sure if that answers your question, but perhaps not sure if I
> understand your question yet?

I just looked at the code again and I think I completely misunderstood
the logic of  BPF_JMP | BPF_CALL.
I think each helper function is working like this.

____helper_function(u32 a1, u32 a2){
}

helper_function(u64 a1, u64 a2){
     ____helper_function((u32 *)a1, (u32 *)a2);
}

So ultimately, we call helper_function which takes u64 as arguments
only. I know its asking a lot, but can you please confirm this asap? I
would like to start implementing it.

>
> Cheers,
> Daniel

-Shubham