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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 72EBBC433F5 for ; Wed, 16 Feb 2022 17:03:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236870AbiBPRD1 (ORCPT ); Wed, 16 Feb 2022 12:03:27 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:32852 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236862AbiBPRDX (ORCPT ); Wed, 16 Feb 2022 12:03:23 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id F384A16201F for ; Wed, 16 Feb 2022 09:03:10 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1645030990; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=XwunH2DjI7pFdcpeiWUDm/kpK6CfJVOijKSMOBToDFg=; b=FbRjioSM/omvO1tgMXjZO3tzANXj6Sk2llkpc+ut/ijuxGcuL2DvZ+PVqoaBZdOIvSNG9Q 8rvfxsH7NuHiE43PxdeKmJoqTfi5RVpvGxEqR53URx5JQYlAISqZBPnDhSFwIv1F0ZBGPl mUEEbelz24CE7K6z3Ttxflczmo90e7Q= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-81-gQYbUko9OWOMsN9ib_JuJg-1; Wed, 16 Feb 2022 12:03:06 -0500 X-MC-Unique: gQYbUko9OWOMsN9ib_JuJg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9760E1800D50; Wed, 16 Feb 2022 17:03:05 +0000 (UTC) Received: from redhat.com (unknown [10.22.8.49]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 17B22753EA; Wed, 16 Feb 2022 17:03:04 +0000 (UTC) Date: Wed, 16 Feb 2022 12:03:03 -0500 From: Joe Lawrence To: live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org Subject: Re: [RFC PATCH v6 10/12] livepatch/selftests: add __asm__ symbol renaming examples Message-ID: References: <20220216163940.228309-1-joe.lawrence@redhat.com> <20220216163940.228309-11-joe.lawrence@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220216163940.228309-11-joe.lawrence@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 16, 2022 at 11:39:38AM -0500, Joe Lawrence wrote: > GCC can rename symbols like static data and optimized functions, adding > a suffix that includes illegal C characters. Extend the klp-convert > examples to demonstrate how to use __asm__ renaming from C code to > create klp-relocations to such renamed symbols. > > Signed-off-by: Joe Lawrence > --- > lib/livepatch/test_klp_convert.h | 2 ++ > lib/livepatch/test_klp_convert1.c | 8 ++++++++ > lib/livepatch/test_klp_convert_mod_a.c | 6 ++++++ > lib/livepatch/test_klp_convert_mod_b.c | 6 ++++++ > tools/testing/selftests/livepatch/test-livepatch.sh | 4 ++++ > 5 files changed, 26 insertions(+) > > diff --git a/lib/livepatch/test_klp_convert.h b/lib/livepatch/test_klp_convert.h > index 5d97bc546d6e..42befbfd63cb 100644 > --- a/lib/livepatch/test_klp_convert.h > +++ b/lib/livepatch/test_klp_convert.h > @@ -10,5 +10,7 @@ extern char driver_name[]; > extern char homonym_string[]; > extern const char *get_homonym_string(void); > extern const char *test_klp_get_driver_name(void); > +extern char klp_string_a[] __asm__("klp_string.12345"); > +extern char klp_string_b[] __asm__("klp_string.67890"); > > #endif > diff --git a/lib/livepatch/test_klp_convert1.c b/lib/livepatch/test_klp_convert1.c > index cd2d3c638258..06926cf1c609 100644 > --- a/lib/livepatch/test_klp_convert1.c > +++ b/lib/livepatch/test_klp_convert1.c > @@ -25,6 +25,12 @@ void print_homonym_string(void) > pr_info("get_homonym_string(), 1: %s\n", get_homonym_string()); > } > > +void print_static_strings(void) > +{ > + pr_info("klp_string.12345 = %s\n", klp_string_a); > + pr_info("klp_string.67890 = %s\n", klp_string_b); > +} > + > /* provide a sysfs handle to invoke debug functions */ > static int print_debug; > static int print_debug_set(const char *val, const struct kernel_param *kp) > @@ -32,6 +38,7 @@ static int print_debug_set(const char *val, const struct kernel_param *kp) > print_saved_command_line(); > print_driver_name(); > print_homonym_string(); > + print_static_strings(); > > return 0; > } > @@ -67,6 +74,7 @@ KLP_MODULE_RELOC(test_klp_convert_mod) test_klp_convert_mod_relocs_a[] = { > KLP_SYMPOS(homonym_string, 1), > KLP_SYMPOS(get_homonym_string, 1), > KLP_SYMPOS(test_klp_get_driver_name, 0), > + KLP_SYMPOS(klp_string_b, 1), > }; > > static struct klp_func funcs[] = { > diff --git a/lib/livepatch/test_klp_convert_mod_a.c b/lib/livepatch/test_klp_convert_mod_a.c > index ae5e911fbb9b..9af0fcab0c8d 100644 > --- a/lib/livepatch/test_klp_convert_mod_a.c > +++ b/lib/livepatch/test_klp_convert_mod_a.c > @@ -20,6 +20,12 @@ __used static const char *get_homonym_string(void) > return homonym_string; > } > > +__used static void static_string_function(void) > +{ > + __used static char klp_string[] __asm__("klp_string.12345") = > + __FILE__ " static string"; > +} > + > MODULE_LICENSE("GPL"); > MODULE_AUTHOR("Joe Lawrence "); > MODULE_DESCRIPTION("Livepatch test: klp-convert module"); > diff --git a/lib/livepatch/test_klp_convert_mod_b.c b/lib/livepatch/test_klp_convert_mod_b.c > index 5eca8a4cae38..0a68e898fe03 100644 > --- a/lib/livepatch/test_klp_convert_mod_b.c > +++ b/lib/livepatch/test_klp_convert_mod_b.c > @@ -11,3 +11,9 @@ __used static const char *get_homonym_string(void) > { > return homonym_string; > } > + > +__used static void static_string_function(void) > +{ > + __used static char klp_string[] __asm__("klp_string.67890") = > + __FILE__ " static string"; > +} > diff --git a/tools/testing/selftests/livepatch/test-livepatch.sh b/tools/testing/selftests/livepatch/test-livepatch.sh > index bcb8b468b80a..ec3b6c919b01 100755 > --- a/tools/testing/selftests/livepatch/test-livepatch.sh > +++ b/tools/testing/selftests/livepatch/test-livepatch.sh > @@ -200,6 +200,8 @@ $MOD_KLP_CONVERT1: driver_name, 0: $MOD_KLP_CONVERT_MOD > $MOD_KLP_CONVERT1: test_klp_get_driver_name(), 0: $MOD_KLP_CONVERT_MOD > $MOD_KLP_CONVERT1: homonym_string, 1: homonym string A > $MOD_KLP_CONVERT1: get_homonym_string(), 1: homonym string A > +test_klp_convert1: klp_string.12345 = lib/livepatch/test_klp_convert_mod_a.c static string > +test_klp_convert1: klp_string.67890 = lib/livepatch/test_klp_convert_mod_b.c static string > % echo 0 > /sys/kernel/livepatch/$MOD_KLP_CONVERT1/enabled > livepatch: '$MOD_KLP_CONVERT1': initializing unpatching transition > livepatch: '$MOD_KLP_CONVERT1': starting unpatching transition > @@ -265,6 +267,8 @@ $MOD_KLP_CONVERT1: driver_name, 0: $MOD_KLP_CONVERT_MOD > $MOD_KLP_CONVERT1: test_klp_get_driver_name(), 0: $MOD_KLP_CONVERT_MOD > $MOD_KLP_CONVERT1: homonym_string, 1: homonym string A > $MOD_KLP_CONVERT1: get_homonym_string(), 1: homonym string A > +test_klp_convert1: klp_string.12345 = lib/livepatch/test_klp_convert_mod_a.c static string > +test_klp_convert1: klp_string.67890 = lib/livepatch/test_klp_convert_mod_b.c static string > % echo 0 > /sys/kernel/livepatch/$MOD_KLP_CONVERT1/enabled > livepatch: '$MOD_KLP_CONVERT1': initializing unpatching transition > livepatch: '$MOD_KLP_CONVERT1': starting unpatching transition > -- > 2.26.3 > I'm not sure how portable it is using __asm__("new.name"), but it seems to work with versions of GCC that I've tried. Other tools like kpatch-build can manipulate such symbols directly, but for anything that needs to feed the C compiler, some kind of workaround is needed to create klp-relocations for them. FWIW, the trick works through the KLP_SYMPOS macro annotations as well, for example: void pfn_valid_part_0(void) __asm__("pfn_valid.part.0"); KLP_MODULE_RELOC(kvm) kvm_main_relocs[] = { KLP_SYMPOS(pfn_valid_part_0, 0), }; -- Joe