On Tue, Jul 25, 2023 at 9:15 AM Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote: > > On Tue, Jul 25, 2023 at 7:03 AM Dave Thaler <dthaler@xxxxxxxxxxxxx> wrote: > > > > I am forwarding the email below (after converting HTML to plain text) > > to the mailto:bpf@xxxxxxxxxxxxxxx list so replies can go to both lists. > > > > Please use this one for any replies. > > > > Thanks, > > Dave > > > > > From: Bpf <bpf-bounces@xxxxxxxx> On Behalf Of Watson Ladd > > > Sent: Monday, July 24, 2023 10:05 PM > > > To: bpf@xxxxxxxx > > > Subject: [Bpf] Review of draft-thaler-bpf-isa-01 > > > > > > Dear BPF wg, > > > > > > I took a look at the draft and think it has some issues, unsurprisingly at this stage. One is > > > the specification seems to use an underspecified C pseudo code for operations vs > > > defining them mathematically. > > Hi Watson, > > This is not "underspecified C" pseudo code. > This is assembly syntax parsed and emitted by GCC, LLVM, gas, Linux Kernel, etc. I don't see a reference to any description of that in section 4.1. It's possible I've overlooked this, and if people think this style of definition is good enough that works for me. But I found table 4 pretty scanty on what exactly happens. > > > > The good news is I think this is very fixable although tedious. > > > > > > The other thornier issues are memory model etc. But the overall structure seems good > > > and the document overall makes sense. > > What do you mean by "memory model" ? > Do you see a reference to it ? Please be specific. No, and that's the problem. Section 5.2 talks about atomic operations. I'd expect that to be paired with a description of barriers so that these work, or a big warning about when you need to use them. For clarity I'm pretty unfamiliar with bpf as a technology, and it's possible that with more knowledge this would make sense. On looking back on that I don't even know if the memory space is flat, or segmented: can I access maps through a value set to dst+offset, or must I always used index? I'm just very confused. Sincerely, Watson -- Astra mortemque praestare gradatim
