netdev - Re: [PATCH bpf-next] selftests/bpf: Fix test_attach

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Date:   Tue, 2 Mar 2021 11:35:03 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Yonghong Song <yhs@...com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andriin@...com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Yauheni Kaliuta <ykaliuta@...hat.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH bpf-next] selftests/bpf: Fix test_attach_probe for
 powerpc uprobes

On Mon, Mar 01, 2021 at 02:58:53PM -0800, Yonghong Song wrote:
> 
> 
> On 3/1/21 11:04 AM, Jiri Olsa 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).
> 
> Any documentation in the kernel about this behavior? This will
> help to validate the change without trying with powerpc64 qemu...

we got similar fix in perf:

7b6ff0bdbf4f perf probe ppc64le: Fixup function entry if using kallsyms lookup

CC-ing few other folks from ppc land for more info

jirka

> 
> > + */
> > +#define LEP_OFFSET 8
> > +
> > +static ssize_t get_offset(ssize_t offset)
> > +{
> > +	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"))
> > 
>