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=-13.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 78EC0C4360C for ; Sun, 29 Sep 2019 21:05:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 560312081B for ; Sun, 29 Sep 2019 21:05:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729072AbfI2VFU (ORCPT ); Sun, 29 Sep 2019 17:05:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50946 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726390AbfI2VFU (ORCPT ); Sun, 29 Sep 2019 17:05:20 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id ABEF1859FF; Sun, 29 Sep 2019 21:05:19 +0000 (UTC) Received: from krava (ovpn-204-49.brq.redhat.com [10.40.204.49]) by smtp.corp.redhat.com (Postfix) with SMTP id 5240360C4B; Sun, 29 Sep 2019 21:05:15 +0000 (UTC) Date: Sun, 29 Sep 2019 23:05:14 +0200 From: Jiri Olsa To: Ian Rogers Cc: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Namhyung Kim , Andi Kleen , linux-kernel@vger.kernel.org, Stephane Eranian Subject: Re: [PATCH v2] perf tools: avoid sample_reg_masks being const + weak Message-ID: <20190929210514.GC602@krava> References: <20190927211005.147176-1-irogers@google.com> <20190927214341.170683-1-irogers@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190927214341.170683-1-irogers@google.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Sun, 29 Sep 2019 21:05:19 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 27, 2019 at 02:43:41PM -0700, Ian Rogers wrote: > Being const + weak breaks with some compilers that constant-propagate > from the weak symbol. This behavior is outside of the specification, but > in LLVM is chosen to match GCC's behavior. > > LLVM's implementation was set in this patch: > https://github.com/llvm/llvm-project/commit/f49573d1eedcf1e44893d5a062ac1b72c8419646 > A const + weak symbol is set to be weak_odr: > https://llvm.org/docs/LangRef.html > ODR is one definition rule, and given there is one constant definition > constant-propagation is possible. It is possible to get this code to > miscompile with LLVM when applying link time optimization. As compilers > become more aggressive, this is likely to break in more instances. > > Move the definition of sample_reg_masks to the conditional part of > perf_regs.h and guard usage with HAVE_PERF_REGS_SUPPORT. This avoids the > weak symbol. > > Fix an issue when HAVE_PERF_REGS_SUPPORT isn't defined from patch v1. > > Signed-off-by: Ian Rogers Acked-by: Jiri Olsa thanks, jirka > --- > tools/perf/util/parse-regs-options.c | 8 ++++++-- > tools/perf/util/perf_regs.c | 4 ---- > tools/perf/util/perf_regs.h | 4 ++-- > 3 files changed, 8 insertions(+), 8 deletions(-) > > diff --git a/tools/perf/util/parse-regs-options.c b/tools/perf/util/parse-regs-options.c > index ef46c2848808..e687497b3aac 100644 > --- a/tools/perf/util/parse-regs-options.c > +++ b/tools/perf/util/parse-regs-options.c > @@ -13,7 +13,7 @@ static int > __parse_regs(const struct option *opt, const char *str, int unset, bool intr) > { > uint64_t *mode = (uint64_t *)opt->value; > - const struct sample_reg *r; > + const struct sample_reg *r = NULL; > char *s, *os = NULL, *p; > int ret = -1; > uint64_t mask; > @@ -46,19 +46,23 @@ __parse_regs(const struct option *opt, const char *str, int unset, bool intr) > > if (!strcmp(s, "?")) { > fprintf(stderr, "available registers: "); > +#ifdef HAVE_PERF_REGS_SUPPORT > for (r = sample_reg_masks; r->name; r++) { > if (r->mask & mask) > fprintf(stderr, "%s ", r->name); > } > +#endif > fputc('\n', stderr); > /* just printing available regs */ > return -1; > } > +#ifdef HAVE_PERF_REGS_SUPPORT > for (r = sample_reg_masks; r->name; r++) { > if ((r->mask & mask) && !strcasecmp(s, r->name)) > break; > } > - if (!r->name) { > +#endif > + if (!r || !r->name) { > ui__warning("Unknown register \"%s\", check man page or run \"perf record %s?\"\n", > s, intr ? "-I" : "--user-regs="); > goto error; > diff --git a/tools/perf/util/perf_regs.c b/tools/perf/util/perf_regs.c > index 2774cec1f15f..5ee47ae1509c 100644 > --- a/tools/perf/util/perf_regs.c > +++ b/tools/perf/util/perf_regs.c > @@ -3,10 +3,6 @@ > #include "perf_regs.h" > #include "event.h" > > -const struct sample_reg __weak sample_reg_masks[] = { > - SMPL_REG_END > -}; > - > int __weak arch_sdt_arg_parse_op(char *old_op __maybe_unused, > char **new_op __maybe_unused) > { > diff --git a/tools/perf/util/perf_regs.h b/tools/perf/util/perf_regs.h > index 47fe34e5f7d5..e014c2c038f4 100644 > --- a/tools/perf/util/perf_regs.h > +++ b/tools/perf/util/perf_regs.h > @@ -15,8 +15,6 @@ struct sample_reg { > #define SMPL_REG2(n, b) { .name = #n, .mask = 3ULL << (b) } > #define SMPL_REG_END { .name = NULL } > > -extern const struct sample_reg sample_reg_masks[]; > - > enum { > SDT_ARG_VALID = 0, > SDT_ARG_SKIP, > @@ -27,6 +25,8 @@ uint64_t arch__intr_reg_mask(void); > uint64_t arch__user_reg_mask(void); > > #ifdef HAVE_PERF_REGS_SUPPORT > +extern const struct sample_reg sample_reg_masks[]; > + > #include > > #define DWARF_MINIMAL_REGS ((1ULL << PERF_REG_IP) | (1ULL << PERF_REG_SP)) > -- > 2.23.0.444.g18eeb5a265-goog >