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Date: Tue, 2 Mar 2021 09:19:49 -0800 From: Yonghong Song <yhs@...com> To: Jiri Olsa <jolsa@...hat.com>, 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>, 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 3/2/21 3:14 AM, Jiri Olsa 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@...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 Thanks. The patch 7b6ff0bdbf4f perf probe ppc64le: Fixup function entry if using kallsyms lookup talked about offset + 8 for kernel symbols. I guess uprobe symbol might be in the same situation if using the same compilation mechanism as kernel. But it would be good to get confirmation from ppc people. > > 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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