netdev - Re: [RFCv2 07/16] bpf: enable non-core use of the verfier

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Message-ID: <20160830204826.GA71063@ast-mbp.thefacebook.com>
Date:   Tue, 30 Aug 2016 13:48:27 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jakub Kicinski <kubakici@...pl>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        netdev@...r.kernel.org, ast@...nel.org,
        dinan.gunawardena@...ronome.com, jiri@...nulli.us,
        john.fastabend@...il.com
Subject: Re: [RFCv2 07/16] bpf: enable non-core use of the verfier

On Tue, Aug 30, 2016 at 10:22:46PM +0200, Jakub Kicinski wrote:
> On Tue, 30 Aug 2016 21:07:50 +0200, Daniel Borkmann wrote:
> > > Having two modes seems more straight forward and I think we would only
> > > need to pay attention in the LD_IMM64 case, I don't think I've seen
> > > LLVM generating XORs, it's just the cBPF -> eBPF conversion.  
> > 
> > Okay, though, I think that the cBPF to eBPF migration wouldn't even
> > pass through the bpf_parse() handling, since verifier is not aware on
> > some of their aspects such as emitting calls directly (w/o *proto) or
> > arg mappings. Probably make sense to reject these (bpf_prog_was_classic())
> > if they cannot be handled anyway?
> 
> TBH again I only use cBPF for testing.  It's a convenient way of
> generating certain instruction sequences.  I can probably just drop
> it completely but the XOR patch is just 3 lines of code so not a huge
> cost either...  I'll keep patch 6 in my tree for now.  

if xor matching is only need for classic, I would drop that patch
just to avoid unnecessary state collection. The number of lines
is not a concern, but extra state for state prunning is.

> Alternatively - is there any eBPF assembler out there?  Something
> converting verifier output back into ELF would be quite cool.

would certainly be nice. I don't think there is anything standalone.
btw llvm can be made to work as assembler only, but simple flex/bison
is probably better.