netdev - Re: [RFC bpf-next v3 03/12] bpf: verifier: remove dead code

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Message-ID: <20181231142750.0f93d3fa@cakuba.hsd1.ca.comcast.net>
Date:   Mon, 31 Dec 2018 14:27:50 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Yonghong Song <yhs@...com>
Cc:     "alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "oss-drivers@...ronome.com" <oss-drivers@...ronome.com>
Subject: Re: [RFC bpf-next v3 03/12] bpf: verifier: remove dead code

On Mon, 31 Dec 2018 21:41:22 +0000, Yonghong Song wrote:
> > func2 after func adjust will start at off and there is no line info for
> > off + cnt (insn4), so we will preserve line_info2.  
> 
> Thanks for verification, I missed that
>  >>> +	/* count lines to be removed */
>  >>> +	l_off = i;
>  >>> +	l_cnt = 0;
>  >>> +	for (; i < nr_linfo; i++)
>  >>> +		if (linfo[i].insn_off < off + cnt)
>  >>> +			l_cnt++;
>  >>> +		else
>  >>> +			break;  
> once you reached linfo[i].insn_off >= off + cnt, no more counting.
> since l_cnt starts from 0, so the last one is actually preserved.

Ah, I see!

> > linfo1:
> > 	insn1
> > 	insn2 /* dead */
> > linfo2:
> > 	insn3 /* dead */
> > 	insn4
> > linfo3:
> > 	insn5
> > 
> >    ||
> >    \/
> > 
> > linfo1:
> > 	insn1
> > linfo2:
> > 	insn4
> > linfo3:
> > 	insn5  
> 
> Yes, the above is the desirable output.

Perfect, let me respin.