netdev - Re: [PATCH bpf-next v3 4/4] bpf_trace: pass array of u64 values in kprobe

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Date:   Thu, 19 May 2022 16:43:09 +0200
From:   Eugene Syromiatnikov <esyr@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Shuah Khan <shuah@...nel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 4/4] bpf_trace: pass array of u64 values in
 kprobe_multi.addrs

On Wed, May 18, 2022 at 04:50:58PM -0700, Andrii Nakryiko wrote:
> On Tue, May 17, 2022 at 12:37 AM Eugene Syromiatnikov <esyr@...hat.com> wrote:
> >
> > With the interface as defined, it is impossible to pass 64-bit kernel
> > addresses from a 32-bit userspace process in BPF_LINK_TYPE_KPROBE_MULTI,
> > which severly limits the useability of the interface, change the ABI
> > to accept an array of u64 values instead of (kernel? user?) longs.
> > Interestingly, the rest of the libbpf infrastructure uses 64-bit values
> > for kallsyms addresses already, so this patch also eliminates
> > the sym_addr cast in tools/lib/bpf/libbpf.c:resolve_kprobe_multi_cb().
> >
> > Fixes: 0dcac272540613d4 ("bpf: Add multi kprobe link")
> > Fixes: 5117c26e877352bc ("libbpf: Add bpf_link_create support for multi kprobes")
> > Fixes: ddc6b04989eb0993 ("libbpf: Add bpf_program__attach_kprobe_multi_opts function")
> > Fixes: f7a11eeccb111854 ("selftests/bpf: Add kprobe_multi attach test")
> > Fixes: 9271a0c7ae7a9147 ("selftests/bpf: Add attach test for bpf_program__attach_kprobe_multi_opts")
> > Fixes: 2c6401c966ae1fbe ("selftests/bpf: Add kprobe_multi bpf_cookie test")
> > Signed-off-by: Eugene Syromiatnikov <esyr@...hat.com>
> > ---
> >  kernel/trace/bpf_trace.c                           | 25 ++++++++++++++++++----
> 
> kernel changes should go into a separate patch

Sure, they can be split, the only reason they are this way is to keep
API/ABI in sync between the kernel code and the user space one.

> (and seems like they
> logically fit together with patch #3, no?)

Patch #3 doesn't change the API/ABI, it only fixes the implementation
in terms of compat handling (and it is more straightforward),
that is why I decided to have it separately. The compat handling
of addrs, on the other hand, can't be fixed without the ABI change.

> >  tools/lib/bpf/bpf.h                                |  2 +-
> >  tools/lib/bpf/libbpf.c                             |  8 +++----
> >  tools/lib/bpf/libbpf.h                             |  2 +-
> >  .../testing/selftests/bpf/prog_tests/bpf_cookie.c  |  2 +-
> >  .../selftests/bpf/prog_tests/kprobe_multi_test.c   |  8 +++----
> >  6 files changed, 32 insertions(+), 15 deletions(-)
> >
> 
> [...]
>