netdev - Re: [PATCH bpf-next 0/3] libbpf: auto-resize relocatable LOAD/STORE instructions

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Date:   Wed, 7 Oct 2020 11:01:02 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Luka Perkov <luka.perkov@...tura.hr>
Cc:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        Tony Ambardar <tony.ambardar@...il.com>,
        Juraj Vijtiuk <juraj.vijtiuk@...tura.hr>,
        Luka Oreskovic <luka.oreskovic@...tura.hr>,
        Sven Fijan <sven.fijan@...tura.hr>,
        David Marcinkovic <david.marcinkovic@...tura.hr>,
        Jakov Petrina <jakov.petrina@...tura.hr>
Subject: Re: [PATCH bpf-next 0/3] libbpf: auto-resize relocatable LOAD/STORE instructions

On Wed, Oct 7, 2020 at 10:56 AM Luka Perkov <luka.perkov@...tura.hr> wrote:
>
> Hello Andrii,
>
> On Fri, Oct 2, 2020 at 3:09 AM Andrii Nakryiko <andriin@...com> wrote:
> > Patch set implements logic in libbpf to auto-adjust memory size (1-, 2-, 4-,
> > 8-bytes) of load/store (LD/ST/STX) instructions which have BPF CO-RE field
> > offset relocation associated with it. In practice this means transparent
> > handling of 32-bit kernels, both pointer and unsigned integers. Signed
> > integers are not relocatable with zero-extending loads/stores, so libbpf
> > poisons them and generates a warning. If/when BPF gets support for sign-extending
> > loads/stores, it would be possible to automatically relocate them as well.
> >
> > All the details are contained in patch #1 comments and commit message.
> > Patch #2 is a simple change in libbpf to make advanced testing with custom BTF
> > easier. Patch #3 validates correct uses of auto-resizable loads, as well as
> > check that libbpf fails invalid uses.
> >
> > I'd really appreciate folks that use BPF on 32-bit architectures to test this
> > out with their BPF programs and report if there are any problems with the
> > approach.
> >
> > Cc: Luka Perkov <luka.perkov@...tura.hr>
>
> First, thank you for the support and sending this series. It took us a
> bit longer to run the tests as our target hardware still did not fully
> get complete mainline support and we had to rebase our patches. These
> are not related to BPF.
>
> Related to this patch, we have tested various BPF programs with this
> patch, and can confirm that it fixed previous issues with pointer
> offsets that we had and reported at:
>
> https://lore.kernel.org/r/CA+XBgLU=8PFkP8S32e4gpst0=R4MFv8rZA5KaO+cEPYSnTRYYw@mail.gmail.com/.
>
> Most of our programs now work and we are currently debugging other
> programs that still aren't working. We are still not sure if the
> remaining issues are related to this or not, but will let you know
> sometime this week after further and more detailed investigation.
>

Ok, great, thanks for the update.

> Thanks,
> Luka