Re: [Bpf] [PATCH v3] bpf, docs: Add additional ABI working draft base text

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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.
"""

See [1].

If you want this document to just be the psABI for Linux, then that is
what we will do -- you are the expert and I am just the drafter.

[1] https://www.sco.com/developers/gabi/
Will





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