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=-10.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 DBEB3C433ED for ; Thu, 23 Jul 2020 11:52:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BAD0A20684 for ; Thu, 23 Jul 2020 11:52:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728412AbgGWLwZ (ORCPT ); Thu, 23 Jul 2020 07:52:25 -0400 Received: from foss.arm.com ([217.140.110.172]:44500 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727940AbgGWLwY (ORCPT ); Thu, 23 Jul 2020 07:52:24 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 48C3AD6E; Thu, 23 Jul 2020 04:52:23 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.6.96]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3BAB13F718; Thu, 23 Jul 2020 04:52:22 -0700 (PDT) Date: Thu, 23 Jul 2020 12:52:16 +0100 From: Mark Rutland To: gregory.herrero@oracle.com Cc: linux-kernel@vger.kernel.org, rostedt@goodmis.org, stable@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com Subject: Re: [PATCH] recordmcount: only record relocation of type R_AARCH64_CALL26 on arm64. Message-ID: <20200723115216.GA17032@C02TD0UTHF1T.local> References: <20200717143338.19302-1-gregory.herrero@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200717143338.19302-1-gregory.herrero@oracle.com> Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org Hi Gregory, As a general thing, for patches affecting arm64 could you please Cc the linx-arm-kernel mailing list (linux-arm-kernel@lists.infradead.org). Some folk working on arm/arm64 aren't subscribed to LKML, and it means patches like this may get missed. On Fri, Jul 17, 2020 at 04:33:38PM +0200, gregory.herrero@oracle.com wrote: > From: Gregory Herrero > > Currently, if a section has a relocation to '_mcount' symbol, a new > __mcount_loc entry will be added whatever the relocation type is. > This is problematic when a relocation to '_mcount' is in the middle of a > section and is not a call for ftrace use. > > Such relocation could be generated with below code for example: > bool is_mcount(unsigned long addr) > { > return (target == (unsigned long) &_mcount); > } > > With this snippet of code, ftrace will try to patch the mcount location > generated by this code on module load and fail with: > > Call trace: > ftrace_bug+0xa0/0x28c > ftrace_process_locs+0x2f4/0x430 > ftrace_module_init+0x30/0x38 > load_module+0x14f0/0x1e78 > __do_sys_finit_module+0x100/0x11c > __arm64_sys_finit_module+0x28/0x34 > el0_svc_common+0x88/0x194 > el0_svc_handler+0x38/0x8c > el0_svc+0x8/0xc > ---[ end trace d828d06b36ad9d59 ]--- > ftrace failed to modify > [] 0xffffa2dbf3a3a41c > actual: 66:a9:3c:90 > Initializing ftrace call sites > ftrace record flags: 2000000 > (0) > expected tramp: ffffa2dc6cf66724 Which code specifically is this triggering for? Is this something in an upstream kernel, or out-of-tree patches? Can you say which toolchain you're using, too? > So Limit the relocation type to R_AARCH64_CALL26 as in perl version of > recordmcount. Given our patching code expects each callsite to be: bl _mcount ... this looks sane to me, and I *think* that's sound for modules too. > Fixes: ed60453fa8f8 ("ARM: 6511/1: ftrace: add ARM support for C version of recordmcount") That's a 32-bit arm commit. I suspect that was meant to be: Fixes: af64d2aa872a1747 ("ftrace: Add arm64 support to recordmcount") > Signed-off-by: Gregory Herrero > --- > scripts/recordmcount.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c > index 7225107a9aaf..e59022b3f125 100644 > --- a/scripts/recordmcount.c > +++ b/scripts/recordmcount.c > @@ -434,6 +434,11 @@ static int arm_is_fake_mcount(Elf32_Rel const *rp) > return 1; > } > > +static int arm64_is_fake_mcount(Elf64_Rel const *rp) > +{ > + return ELF64_R_TYPE(w(rp->r_info)) != R_AARCH64_CALL26; > +} > + > /* 64-bit EM_MIPS has weird ELF64_Rela.r_info. > * http://techpubs.sgi.com/library/manuals/4000/007-4658-001/pdf/007-4658-001.pdf > * We interpret Table 29 Relocation Operation (Elf64_Rel, Elf64_Rela) [p.40] > @@ -547,6 +552,7 @@ static int do_file(char const *const fname) > make_nop = make_nop_arm64; > rel_type_nop = R_AARCH64_NONE; > ideal_nop = ideal_nop4_arm64; > + is_fake_mcount64 = arm64_is_fake_mcount; > break; As above, I think this is sound, but if you could answer my questions that'd be helpful. Thanks, Mark. > case EM_IA_64: reltype = R_IA64_IMM64; break; > case EM_MIPS: /* reltype: e_class */ break; > -- > 2.27.0 >