BPF Archive on lore.kernel.org
 help / color / Atom feed
From: Jiri Olsa <jolsa@redhat.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: "Jiri Olsa" <jolsa@kernel.org>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Andrii Nakryiko" <andriin@fb.com>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	"Martin KaFai Lau" <kafai@fb.com>,
	"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"KP Singh" <kpsingh@chromium.org>,
	"Toke Høiland-Jørgensen" <toke@redhat.com>,
	"Yauheni Kaliuta" <ykaliuta@redhat.com>
Subject: Re: [PATCH bpf-next] selftests/bpf: Fix test_attach_probe for powerpc uprobes
Date: Tue, 2 Mar 2021 19:58:38 +0100
Message-ID: <YD6K3nex6MQ09u8U@krava> (raw)
In-Reply-To: <CAEf4Bzah8Au01NvtwSogpkr3etwQ3_bObj3GObG8Lb3N0DqZwA@mail.gmail.com>

On Tue, Mar 02, 2021 at 10:31:41AM -0800, Andrii Nakryiko wrote:
> On Tue, Mar 2, 2021 at 3:14 AM Jiri Olsa <jolsa@redhat.com> wrote:
> >
> > On Mon, Mar 01, 2021 at 04:34:24PM -0800, Andrii Nakryiko wrote:
> > > On Mon, Mar 1, 2021 at 11:11 AM Jiri Olsa <jolsa@kernel.org> wrote:
> > > >
> > > > When testing uprobes we the test gets GEP (Global Entry Point)
> > > > address from kallsyms, but then the function is called locally
> > > > so the uprobe is not triggered.
> > > >
> > > > Fixing this by adjusting the address to LEP (Local Entry Point)
> > > > for powerpc arch.
> > > >
> > > > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > > > ---
> > > >  .../selftests/bpf/prog_tests/attach_probe.c    | 18 +++++++++++++++++-
> > > >  1 file changed, 17 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/tools/testing/selftests/bpf/prog_tests/attach_probe.c b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
> > > > index a0ee87c8e1ea..c3cfb48d3ed0 100644
> > > > --- a/tools/testing/selftests/bpf/prog_tests/attach_probe.c
> > > > +++ b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
> > > > @@ -2,6 +2,22 @@
> > > >  #include <test_progs.h>
> > > >  #include "test_attach_probe.skel.h"
> > > >
> > > > +#if defined(__powerpc64__)
> > > > +/*
> > > > + * We get the GEP (Global Entry Point) address from kallsyms,
> > > > + * but then the function is called locally, so we need to adjust
> > > > + * the address to get LEP (Local Entry Point).
> > > > + */
> > > > +#define LEP_OFFSET 8
> > > > +
> > > > +static ssize_t get_offset(ssize_t offset)
> > >
> > > if we mark this function __weak global, would it work as is? Would it
> > > get an address of a global entry point? I know nothing about this GEP
> > > vs LEP stuff, interesting :)
> >
> > you mean get_base_addr? it's already global
> >
> > all the calls to get_base_addr within the object are made
> > to get_base_addr+0x8
> >
> > 00000000100350c0 <test_attach_probe>:
> >     ...
> >     100350e0:   59 fd ff 4b     bl      10034e38 <get_base_addr+0x8>
> >     ...
> >     100358a8:   91 f5 ff 4b     bl      10034e38 <get_base_addr+0x8>
> >
> >
> > I'm following perf fix we had for similar issue:
> >   7b6ff0bdbf4f perf probe ppc64le: Fixup function entry if using kallsyms lookup
> >
> > I'll get more info on that
> 
> My thinking was that if you mark the function as __weak, then the
> compiler is not allowed to assume that the actual implementation of
> that function will come from the same object (because it might be
> replaced by the linker later), so it has to be pessimistic and use
> global entry, no? Totally theoritizing here, of course.

ah ok.. good idea, but it's still jumping to +8 in my test

    # nm test_progs | grep get_base_addr
    0000000010034e30 W get_base_addr

    100350e0:   59 fd ff 4b     bl      10034e38 <get_base_addr+0x8>

looks like it's linker, because compiler leaves just jump to next instruction

jirka


      reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-01 19:04 Jiri Olsa
2021-03-01 22:58 ` Yonghong Song
2021-03-02 10:35   ` Jiri Olsa
2021-03-03  6:40     ` Naveen N. Rao
2021-03-03 22:49       ` Jiri Olsa
2021-03-04  0:46       ` Michael Ellerman
2021-03-04 15:55         ` Jiri Olsa
2021-03-04  1:34           ` Naveen N. Rao
2021-03-05 13:38             ` Jiri Olsa
2021-03-02  0:34 ` Andrii Nakryiko
2021-03-02 11:14   ` Jiri Olsa
2021-03-02 17:19     ` Yonghong Song
2021-03-03  6:42       ` Naveen N. Rao
2021-03-02 18:31     ` Andrii Nakryiko
2021-03-02 18:58       ` Jiri Olsa [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YD6K3nex6MQ09u8U@krava \
    --to=jolsa@redhat.com \
    --cc=andrii.nakryiko@gmail.com \
    --cc=andriin@fb.com \
    --cc=ast@kernel.org \
    --cc=bpf@vger.kernel.org \
    --cc=daniel@iogearbox.net \
    --cc=john.fastabend@gmail.com \
    --cc=jolsa@kernel.org \
    --cc=kafai@fb.com \
    --cc=kpsingh@chromium.org \
    --cc=netdev@vger.kernel.org \
    --cc=songliubraving@fb.com \
    --cc=toke@redhat.com \
    --cc=yhs@fb.com \
    --cc=ykaliuta@redhat.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

BPF Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/bpf/0 bpf/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 bpf bpf/ https://lore.kernel.org/bpf \
		bpf@vger.kernel.org
	public-inbox-index bpf

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.bpf


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git