From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757057AbcJMWRt (ORCPT ); Thu, 13 Oct 2016 18:17:49 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42672 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756862AbcJMWRk (ORCPT ); Thu, 13 Oct 2016 18:17:40 -0400 From: Josh Poimboeuf To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, Arnd Bergmann Subject: [PATCH 1/2] objtool: improve rare switch jump table pattern detection Date: Thu, 13 Oct 2016 16:22:52 -0500 Message-Id: <8a9ed68ae1780e8d3963e4ee13f2f257fe3a3c33.1476393584.git.jpoimboe@redhat.com> In-Reply-To: References: X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Thu, 13 Oct 2016 21:22:59 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org gcc 6 added a new switch statement jump table optimization which makes objtool's life harder. It looks like: mov [rodata addr],%reg1 ... some instructions ... jmpq *(%reg1,%reg2,8) The optimization is quite rare, but objtool still needs to be able to identify the pattern so that it can follow all possible control flow paths related to the switch statement. In order to detect the pattern, objtool starts from the indirect jump and scans backwards through the function until it finds the first instruction in the pattern. If it encounters an unconditional jump along the way, it stops and considers the pattern to be not found. As it turns out, unconditional jumps can happen, as long as they are small forward jumps within the range being scanned. This fixes the following warnings: drivers/infiniband/sw/rxe/rxe_comp.o: warning: objtool: rxe_completer()+0x2f4: sibling call from callable instruction with changed frame pointer drivers/infiniband/sw/rxe/rxe_resp.o: warning: objtool: rxe_responder()+0x10f: sibling call from callable instruction with changed frame pointer Reported-by: Arnd Bergmann Signed-off-by: Josh Poimboeuf --- tools/objtool/builtin-check.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c index 143b6cd..a00a05d 100644 --- a/tools/objtool/builtin-check.c +++ b/tools/objtool/builtin-check.c @@ -713,6 +713,7 @@ static struct rela *find_switch_table(struct objtool_file *file, struct instruction *insn) { struct rela *text_rela, *rodata_rela; + struct instruction *orig_insn = insn; text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); if (text_rela && text_rela->sym == file->rodata->sym) { @@ -733,10 +734,16 @@ static struct rela *find_switch_table(struct objtool_file *file, /* case 3 */ func_for_each_insn_continue_reverse(file, func, insn) { - if (insn->type == INSN_JUMP_UNCONDITIONAL || - insn->type == INSN_JUMP_DYNAMIC) + if (insn->type == INSN_JUMP_DYNAMIC) break; + /* allow small jumps within the range */ + if (insn->type == INSN_JUMP_UNCONDITIONAL && + insn->jump_dest && + (insn->jump_dest->offset <= insn->offset || + insn->jump_dest->offset >= orig_insn->offset)) + break; + text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len); if (text_rela && text_rela->sym == file->rodata->sym) -- 2.7.4