From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E8311C433DB for ; Wed, 3 Mar 2021 23:08:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9CE8764F0D for ; Wed, 3 Mar 2021 23:08:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232053AbhCCXCu (ORCPT ); Wed, 3 Mar 2021 18:02:50 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:45239 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1449533AbhCCWwF (ORCPT ); Wed, 3 Mar 2021 17:52:05 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614811821; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=I+ZGM20Ww175B2i0Qx4AwkjsbVbJ+G3IdGtLxfVijYs=; b=S473nnsYFkaqzSS+4is2+6360SecWbErtnSBXs5Vazobxqs6EwKQhFi1hidKEt+wee4/og emyP5Np+Ihg0HyAqXqCTdu2kQFsV1UuTmFf/WeoGNOfGo5L/CdFLdymCAfLb238nTpwGF1 RU2XMSn4ZpwBXass8/K7egyYBV9bhwM= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-88-4KA0ZT6oNeGHCVhnnpNx8A-1; Wed, 03 Mar 2021 17:50:18 -0500 X-MC-Unique: 4KA0ZT6oNeGHCVhnnpNx8A-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3FB97107ACE3; Wed, 3 Mar 2021 22:50:16 +0000 (UTC) Received: from krava (unknown [10.40.196.53]) by smtp.corp.redhat.com (Postfix) with SMTP id 127FF60BE2; Wed, 3 Mar 2021 22:49:59 +0000 (UTC) Date: Wed, 3 Mar 2021 23:49:59 +0100 From: Jiri Olsa To: "Naveen N. Rao" Cc: Yonghong Song , Jiri Olsa , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , netdev@vger.kernel.org, bpf@vger.kernel.org, Martin KaFai Lau , Song Liu , John Fastabend , KP Singh , Toke =?iso-8859-1?Q?H=F8iland-J=F8rgensen?= , Yauheni Kaliuta , Michael Ellerman , Srikar Dronamraju , Paul Mackerras Subject: Re: [PATCH bpf-next] selftests/bpf: Fix test_attach_probe for powerpc uprobes Message-ID: References: <20210301190416.90694-1-jolsa@kernel.org> <309d8d05-4bbd-56b8-6c05-12a1aa98b843@fb.com> <20210303064043.GB1913@DESKTOP-TDPLP67.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210303064043.GB1913@DESKTOP-TDPLP67.localdomain> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Wed, Mar 03, 2021 at 12:10:43PM +0530, Naveen N. Rao wrote: > 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 > > > > --- > > > > .../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 > > > > #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. i see, there's the outer #if _CALL_ELF I missed > > > > > +/* > > > > + * 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 > > > > > 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 > > Thanks. > > > > > > > > + */ > > > > +#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")) > > > > > > As documented in the links above, the right way to identify local entry > point (LEP) is by looking at the symbol table. Falling back to using a > hardcoded offset of 8 is a reasonable workaround if we don't have access > to the symbol table. thanks for the all the info, I'll send v2 with _CALL_ELF check jirka