Subject: Re: [PATCH 3/4] bpf, docs: Generate nicer tables for instruction encodings

From: Christoph Hellwig <[email-masked]>
Date: Mon, 3 Jan 2022 10:57:12 +0100

On Thu, Dec 30, 2021 at 04:43:24PM -0800, Alexei Starovoitov wrote:
> > +  ========  =====  =========================
> > +  code      value  description
> > +  ========  =====  =========================
> > +  BPF_JA    0x00   BPF_JMP only
> >    BPF_JEQ   0x10
> >    BPF_JGT   0x20
> >    BPF_JGE   0x30
> >    BPF_JSET  0x40
> 
> Not your fault, but the new table looks odd with
> only some opcodes documented.
> Same issue with BPF_ALU table.
> In the past the documented opcodes were for eBPF only and
> not documented in both, so it wasn't that bad.
> At least there was a reason for discrepancy.
> Now it just odd.
> May be add a comment to all rows?

Yes, having the description everywhere would be good.  But I'll have to
do research to actually figure out what should go in there for some.

> > +  =============  =====  =====================
> > +  mode modifier  value  description
> > +  =============  =====  =====================
> > +  BPF_IMM        0x00   used for 64-bit mov
> > +  BPF_ABS        0x20
> > +  BPF_IND        0x40
> > +  BPF_MEM        0x60
> 
> May be say here that ABS and IND are legacy for compat with classic only?
> and MEM is the most common modifier for load/store?

Sure.