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Date: Tue, 2 Mar 2021 12:14:01 +0100
From: Jiri Olsa <jolsa@...hat.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andriin@...com>,
Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...omium.org>,
Toke Høiland-Jørgensen <toke@...hat.com>,
Yauheni Kaliuta <ykaliuta@...hat.com>
Subject: Re: [PATCH bpf-next] selftests/bpf: Fix test_attach_probe for
powerpc uprobes
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@...nel.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@...nel.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
jirka
>
> > +{
> > + return offset + LEP_OFFSET;
> > +}
> > +#else
> > +#define get_offset(offset) (offset)
> > +#endif
> > +
> > ssize_t get_base_addr() {
> > size_t start, offset;
> > char buf[256];
> > @@ -36,7 +52,7 @@ void test_attach_probe(void)
> > if (CHECK(base_addr < 0, "get_base_addr",
> > "failed to find base addr: %zd", base_addr))
> > return;
> > - uprobe_offset = (size_t)&get_base_addr - base_addr;
> > + uprobe_offset = get_offset((size_t)&get_base_addr - base_addr);
> >
> > skel = test_attach_probe__open_and_load();
> > if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
> > --
> > 2.29.2
> >
>
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