On Wed, Nov 8, 2023 at 3:57 PM Will Hawkins <hawkinsw@xxxxxx> wrote: > > On Wed, Nov 8, 2023 at 2:51 PM Alexei Starovoitov > <alexei.starovoitov@xxxxxxxxx> wrote: > > > > On Wed, Nov 8, 2023 at 2:13 AM Will Hawkins <hawkinsw@xxxxxx> wrote: > > > > > > On Tue, Nov 7, 2023 at 8:17 PM Alexei Starovoitov > > > <alexei.starovoitov@xxxxxxxxx> wrote: > > > > > > > > On Tue, Nov 7, 2023 at 11:56 AM Will Hawkins <hawkinsw@xxxxxx> wrote: > > > > > > > > > > On Mon, Nov 6, 2023 at 3:38 AM Alexei Starovoitov > > > > > <alexei.starovoitov@xxxxxxxxx> wrote: > > > > > > > > > > > > On Sun, Nov 5, 2023 at 4:17 PM Will Hawkins <hawkinsw@xxxxxx> wrote: > > > > > > > > > > > > > > On Sun, Nov 5, 2023 at 4:51 AM Alexei Starovoitov > > > > > > > <alexei.starovoitov@xxxxxxxxx> wrote: > > > > > > > > > > > > > > > > On Fri, Nov 3, 2023 at 2:20 PM Will Hawkins <hawkinsw@xxxxxx> wrote: > > > > > > > > > + > > > > > > > > > +The ABI is specified in two parts: a generic part and a processor-specific part. > > > > > > > > > +A pairing of generic ABI with the processor-specific ABI for a certain > > > > > > > > > +instantiation of a BPF machine represents a complete binary interface for BPF > > > > > > > > > +programs executing on that machine. > > > > > > > > > + > > > > > > > > > +This document is the generic ABI and specifies the parameters and behavior > > > > > > > > > +common to all instantiations of BPF machines. In addition, it defines the > > > > > > > > > +details that must be specified by each processor-specific ABI. > > > > > > > > > + > > > > > > > > > +These psABIs are the second part of the ABI. Each instantiation of a BPF > > > > > > > > > +machine must describe the mechanism through which binary interface > > > > > > > > > +compatibility is maintained with respect to the issues highlighted by this > > > > > > > > > +document. However, the details that must be defined by a psABI are a minimum -- > > > > > > > > > +a psABI may specify additional requirements for binary interface compatibility > > > > > > > > > +on a platform. > > > > > > > > > > > > > > > > I don't understand what you are trying to say in the above. > > > > > > > > In my mind there is only one BPF psABI and it doesn't have > > > > > > > > generic and processor parts. There is only one "processor". > > > > > > > > BPF is such a processor. > > > > > > > > > > > > > > What I was trying to say was that the document here describes a > > > > > > > generic ABI. In this document there will be areas that are specific to > > > > > > > different implementations and those would be considered processor > > > > > > > specific. In other words, the ubpf runtime could define those things > > > > > > > differently than the rbpf runtime which, in turn, could define those > > > > > > > things differently than the kernel's implementation. > > > > > > > > > > > > I see what you mean. There is only one BPF psABI. There cannot be two. > > > > > > ubpf can decide not to follow it, but it could only mean that > > > > > > it's non conformant and not compatible. > > > > > > > > > > Okay. That was not how I was structuring the ABI. I thought we had > > > > > decided that, as the document said, an instantiation of a machine had > > > > > to > > > > > > > > > > 1. meet the gABI > > > > > 2. specify its requirements vis a vis the psABI > > > > > 3. (optionally) describe other requirements. > > > > > > > > > > If that is not what we decided then we will have to restructure the document. > > > > > > > > This abi.rst file is the beginning of "BPF psABI" document. > > > > We probably should rename it to psabi.rst to avoid confusion. > > > > See my slides from IETF 118. I hope they explain what "BPF psABI" is for. > > > > > > Of course they do! Thank you! My only question: In the language I was > > > using, I was taking a cue from the System V world where there is a > > > Generic ABI and a psABI. The Generic ABI applies to all System V > > > compatible systems and defines certain processor-specific details that > > > each platform must specify to define a complete ABI. In particular, I > > > took this language as inspiration > > > > > > """ > > > The System V ABI is composed of two basic parts: A generic part of the > > > specification describes those parts of the interface that remain > > > constant across all hardware implementations of System V, and a > > > processor-specific part of the specification describes the parts of > > > the specification that are specific to a particular processor > > > architecture. Together, the generic ABI (or gABI) and the processor > > > specific supplement (or psABI) provide a complete interface > > > specification for compiled application programs on systems that share > > > a common hardware architecture. > > > """ > > > > I see where you got the inspiration from, but it's not applicable > > in the BPF case. BPF is such one and only processor. > > We're not changing nor adding anything to Sys V generic parts. > > That was not quite what I was saying. What I started to draft is > something (yes, modeled after the Sys V (g/ps)ABI) but _brand new_ for > BPF. I think that is where I have been failing to communicate > correctly. What I was proposing was inspired by other ABIs but > completely separate and orthogonal. That is the reason for the > document speaking of a BPF Machine like: > > ABI-conforming BPF Machine Instantiation: A physical or logical realization > of a computer system capable of executing BPF programs consistently with the > specifications outlined in this document. > > because it is a (not necessarily physical) entity that executes BPF > programs (i.e. a "BPF CPU") for which we are specifying the binary > compatibility. In other words, the document as it stands is proposing > a gABI where > > the kernel's "BPF CPU" would have its own psABI > ubpf's "BPF CPU" would have its own psABI and how would you expect that to work? psABI is a compiler spec in the first place. The user would use clang -O2 -target bpf_kernel vs -target bpf_ubpf ?
