From: Michael Ellerman <mpe@ellerman.id.au>
To: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
Jiri Olsa <jolsa@redhat.com>
Cc: "Yonghong Song" <yhs@fb.com>, "Jiri Olsa" <jolsa@kernel.org>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Andrii Nakryiko" <andriin@fb.com>,
netdev@vger.kernel.org, bpf@vger.kernel.org,
"Martin KaFai Lau" <kafai@fb.com>,
"Song Liu" <songliubraving@fb.com>,
"John Fastabend" <john.fastabend@gmail.com>,
"KP Singh" <kpsingh@chromium.org>,
"Toke Høiland-Jørgensen" <toke@redhat.com>,
"Yauheni Kaliuta" <ykaliuta@redhat.com>,
"Srikar Dronamraju" <srikar@linux.vnet.ibm.com>,
"Paul Mackerras" <paulus@samba.org>
Subject: Re: [PATCH bpf-next] selftests/bpf: Fix test_attach_probe for powerpc uprobes
Date: Thu, 04 Mar 2021 11:46:27 +1100 [thread overview]
Message-ID: <87blbzsq3g.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <20210303064043.GB1913@DESKTOP-TDPLP67.localdomain>
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> writes:
> On 2021/03/02 11:35AM, Jiri Olsa wrote:
>> 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@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__)
>
> This needs to be specific to ELF v2 ABI, so you'll need to check
> _CALL_ELF. See commit d5c2e2c17ae1d6 ("perf probe ppc64le: Prefer symbol
> table lookup over DWARF") for an example.
>
>> > > +/*
>> > > + * 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...
>
> I don't think we have documented this in the kernel anywhere, but this
> is specific to the ELF v2 ABI and is described there:
> - 2.3.2.1. Function Prologue:
> http://cdn.openpowerfoundation.org/wp-content/uploads/resources/leabi/content/dbdoclet.50655240___RefHeading___Toc377640597.html
> - 3.4.1. Symbol Values:
> http://cdn.openpowerfoundation.org/wp-content/uploads/resources/leabi/content/dbdoclet.50655241_95185.html
There's a comment in ppc_function_entry(), but I don't think we have any
actual "documentation".
static inline unsigned long ppc_function_entry(void *func)
{
#ifdef PPC64_ELF_ABI_v2
u32 *insn = func;
/*
* A PPC64 ABIv2 function may have a local and a global entry
* point. We need to use the local entry point when patching
* functions, so identify and step over the global entry point
* sequence.
*
* The global entry point sequence is always of the form:
*
* addis r2,r12,XXXX
* addi r2,r2,XXXX
*
* A linker optimisation may convert the addis to lis:
*
* lis r2,XXXX
* addi r2,r2,XXXX
*/
if ((((*insn & OP_RT_RA_MASK) == ADDIS_R2_R12) ||
((*insn & OP_RT_RA_MASK) == LIS_R2)) &&
((*(insn+1) & OP_RT_RA_MASK) == ADDI_R2_R2))
return (unsigned long)(insn + 2);
else
return (unsigned long)func;
cheers
next prev parent reply other threads:[~2021-03-04 1:00 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-01 19:04 [PATCH bpf-next] selftests/bpf: Fix test_attach_probe for powerpc uprobes 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 [this message]
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
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=87blbzsq3g.fsf@mpe.ellerman.id.au \
--to=mpe@ellerman.id.au \
--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=jolsa@redhat.com \
--cc=kafai@fb.com \
--cc=kpsingh@chromium.org \
--cc=naveen.n.rao@linux.vnet.ibm.com \
--cc=netdev@vger.kernel.org \
--cc=paulus@samba.org \
--cc=songliubraving@fb.com \
--cc=srikar@linux.vnet.ibm.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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).