From patchwork Thu Nov 16 17:45:37 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Josh Poimboeuf X-Patchwork-Id: 838725 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [103.22.144.68]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 3yd8B067Whz9s72 for ; Fri, 17 Nov 2017 04:58:32 +1100 (AEDT) Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 3yd8B04qwDzDqnM for ; Fri, 17 Nov 2017 04:58:32 +1100 (AEDT) X-Original-To: linuxppc-dev@lists.ozlabs.org Delivered-To: linuxppc-dev@lists.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=redhat.com (client-ip=209.132.183.28; helo=mx1.redhat.com; envelope-from=jpoimboe@redhat.com; receiver=) Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3yd7vF0GL7zDr25 for ; Fri, 17 Nov 2017 04:45:45 +1100 (AEDT) Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4B6091293; Thu, 16 Nov 2017 17:45:43 +0000 (UTC) Received: from treble (ovpn-112-35.rdu2.redhat.com [10.10.112.35]) by smtp.corp.redhat.com (Postfix) with SMTP id 9E28E46E7A; Thu, 16 Nov 2017 17:45:39 +0000 (UTC) Date: Thu, 16 Nov 2017 11:45:37 -0600 From: Josh Poimboeuf To: "Naveen N. Rao" Subject: [PATCH v4.2] powerpc/modules: Don't try to restore r2 after a sibling call Message-ID: <20171116174537.duz4x6vfzhp44lfh@treble> References: <20171114092910.20399-1-kamalesh@linux.vnet.ibm.com> <20171114092910.20399-3-kamalesh@linux.vnet.ibm.com> <1510654928.8xrjtkjm8m.naveen@linux.ibm.com> <20171114155323.3sjxx3eykinnl2ea@treble> <1510737417.g8rnjuztlf.naveen@linux.ibm.com> <20171116012628.6ajxlychto365sf6@treble> <1510837263.5d3ac8knzo.naveen@linux.ibm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1510837263.5d3ac8knzo.naveen@linux.ibm.com> User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Thu, 16 Nov 2017 17:45:43 +0000 (UTC) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.24 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-kernel@vger.kernel.org, Kamalesh Babulal , live-patching@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, Nov 16, 2017 at 06:39:03PM +0530, Naveen N. Rao wrote: > Josh Poimboeuf wrote: > > On Wed, Nov 15, 2017 at 02:58:33PM +0530, Naveen N. Rao wrote: > > > > +int instr_is_link_branch(unsigned int instr) > > > > +{ > > > > + return (instr_is_branch_iform(instr) || instr_is_branch_bform(instr)) && > > > > + (instr & BRANCH_SET_LINK); > > > > +} > > > > + > > > > > > Nitpicking here, but since we're not considering the other branch forms, > > > perhaps this can be renamed to instr_is_link_relative_branch() (or maybe > > > instr_is_relative_branch_link()), just so we're clear :) > > > > My understanding is that the absolute/relative bit isn't a "form", but > > rather a bit that can be set for either the b-form (conditional) or the > > i-form (unconditional). And the above function isn't checking the > > absolute bit, so it isn't necessarily a relative branch. Or did I miss > > something? > > Ah, good point. I was coming from the fact that we are only considering the > i-form and b-form branches and not the lr/ctr/tar based branches, which are > always absolute branches, but can also set the link register. Hm, RISC is more complicated than I realized ;-) > Thinking about this more, aren't we only interested in relative branches > here (for relocations), so can we actually filter out the absolute branches? > Something like this? > > int instr_is_relative_branch_link(unsigned int instr) > { > return ((instr_is_branch_iform(instr) || instr_is_branch_bform(instr)) && > !(instr & BRANCH_ABSOLUTE) && (instr & BRANCH_SET_LINK)); Yeah, makes sense to me. Here's another try (also untested). If this looks ok, Kamalesh would you mind testing again? ----8<---- From: Josh Poimboeuf Subject: [PATCH v4.2] powerpc/modules: Don't try to restore r2 after a sibling call When attempting to load a livepatch module, I got the following error: module_64: patch_module: Expect noop after relocate, got 3c820000 The error was triggered by the following code in unregister_netdevice_queue(): 14c: 00 00 00 48 b 14c 14c: R_PPC64_REL24 net_set_todo 150: 00 00 82 3c addis r4,r2,0 GCC didn't insert a nop after the branch to net_set_todo() because it's a sibling call, so it never returns. The nop isn't needed after the branch in that case. Signed-off-by: Josh Poimboeuf Acked-by: Naveen N. Rao --- arch/powerpc/include/asm/code-patching.h | 1 + arch/powerpc/kernel/module_64.c | 12 +++++++++++- arch/powerpc/lib/code-patching.c | 5 +++++ 3 files changed, 17 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h index abef812de7f8..2c895e8d07f7 100644 --- a/arch/powerpc/include/asm/code-patching.h +++ b/arch/powerpc/include/asm/code-patching.h @@ -33,6 +33,7 @@ int patch_branch(unsigned int *addr, unsigned long target, int flags); int patch_instruction(unsigned int *addr, unsigned int instr); int instr_is_relative_branch(unsigned int instr); +int instr_is_relative_link_branch(unsigned int instr); int instr_is_branch_to_addr(const unsigned int *instr, unsigned long addr); unsigned long branch_target(const unsigned int *instr); unsigned int translate_branch(const unsigned int *dest, diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c index 759104b99f9f..180c16f04063 100644 --- a/arch/powerpc/kernel/module_64.c +++ b/arch/powerpc/kernel/module_64.c @@ -487,7 +487,17 @@ static bool is_early_mcount_callsite(u32 *instruction) restore r2. */ static int restore_r2(u32 *instruction, struct module *me) { - if (is_early_mcount_callsite(instruction - 1)) + u32 *prev_insn = instruction - 1; + + if (is_early_mcount_callsite(prev_insn)) + return 1; + + /* + * Make sure the branch isn't a sibling call. Sibling calls aren't + * "link" branches and they don't return, so they don't need the r2 + * restore afterwards. + */ + if (!instr_is_relative_link_branch(*prev_insn)) return 1; if (*instruction != PPC_INST_NOP) { diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c index c9de03e0c1f1..d81aab7441f7 100644 --- a/arch/powerpc/lib/code-patching.c +++ b/arch/powerpc/lib/code-patching.c @@ -304,6 +304,11 @@ int instr_is_relative_branch(unsigned int instr) return instr_is_branch_iform(instr) || instr_is_branch_bform(instr); } +int instr_is_relative_link_branch(unsigned int instr) +{ + return instr_is_relative_branch(instr) && (instr & BRANCH_SET_LINK); +} + static unsigned long branch_iform_target(const unsigned int *instr) { signed long imm;