From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751530AbdGZTKN (ORCPT ); Wed, 26 Jul 2017 15:10:13 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37388 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751109AbdGZTKM (ORCPT ); Wed, 26 Jul 2017 15:10:12 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 4B3957EAB1 Authentication-Results: ext-mx04.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx04.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=jpoimboe@redhat.com Date: Wed, 26 Jul 2017 14:10:08 -0500 From: Josh Poimboeuf To: Arnd Bergmann Cc: Linux Kernel Mailing List Subject: Re: new objtool unreachable instruction warnings Message-ID: <20170726191008.jk2cdqr4wqnc33es@treble> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Wed, 26 Jul 2017 19:10:12 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 26, 2017 at 04:46:40PM +0200, Arnd Bergmann wrote: > I only saw these warnings once, they are either very rare, or were introduced > recently: > > arch/x86/kvm/vmx.o: warning: objtool: .altinstr_replacement+0x0: > unreachable instruction > arch/x86/kvm/svm.o: warning: objtool: .altinstr_replacement+0x6e: > unreachable instruction > > I see this with gcc-4.6 though gcc-7, but not with gcc-4.3. > > The configuration file that triggered it is > https://pastebin.com/aMn45GYP > > I managed to trace the problem down to the CC_HAVE_ASM_GOTO > macro, without that, we don't run into the problem. Thanks for reporting all these! This should fix all the warnings you reported. I'll split it up into real patches and submit them soon. Let me know if you find anything else. diff --git a/tools/objtool/arch.h b/tools/objtool/arch.h index 21aeca874edb..b0d7dc3d71b5 100644 --- a/tools/objtool/arch.h +++ b/tools/objtool/arch.h @@ -31,8 +31,9 @@ #define INSN_RETURN 6 #define INSN_CONTEXT_SWITCH 7 #define INSN_STACK 8 -#define INSN_NOP 9 -#define INSN_OTHER 10 +#define INSN_BUG 9 +#define INSN_NOP 10 +#define INSN_OTHER 11 #define INSN_LAST INSN_OTHER enum op_dest_type { diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c index a36c2eba64e7..7841e5d31973 100644 --- a/tools/objtool/arch/x86/decode.c +++ b/tools/objtool/arch/x86/decode.c @@ -271,7 +271,7 @@ int arch_decode_instruction(struct elf *elf, struct section *sec, case 0x8d: if (rex == 0x48 && modrm == 0x65) { - /* lea -disp(%rbp), %rsp */ + /* lea disp(%rbp), %rsp */ *type = INSN_STACK; op->src.type = OP_SRC_ADD; op->src.reg = CFI_BP; @@ -281,6 +281,30 @@ int arch_decode_instruction(struct elf *elf, struct section *sec, break; } + if (rex == 0x48 && (modrm == 0xa4 || modrm == 0x64) && + sib == 0x24) { + + /* lea disp(%rsp), %rsp */ + *type = INSN_STACK; + op->src.type = OP_SRC_ADD; + op->src.reg = CFI_SP; + op->src.offset = insn.displacement.value; + op->dest.type = OP_DEST_REG; + op->dest.reg = CFI_SP; + break; + } + + if (rex == 0x48 && modrm == 0x2c && sib == 0x24) { + + /* lea (%rsp), %rbp */ + *type = INSN_STACK; + op->src.type = OP_SRC_REG; + op->src.reg = CFI_SP; + op->dest.type = OP_DEST_REG; + op->dest.reg = CFI_BP; + break; + } + if (rex == 0x4c && modrm == 0x54 && sib == 0x24 && insn.displacement.value == 8) { @@ -382,20 +406,27 @@ int arch_decode_instruction(struct elf *elf, struct section *sec, case 0x0f: - if (op2 >= 0x80 && op2 <= 0x8f) + if (op2 >= 0x80 && op2 <= 0x8f) { + *type = INSN_JUMP_CONDITIONAL; - else if (op2 == 0x05 || op2 == 0x07 || op2 == 0x34 || - op2 == 0x35) + + } else if (op2 == 0x05 || op2 == 0x07 || op2 == 0x34 || + op2 == 0x35) { /* sysenter, sysret */ *type = INSN_CONTEXT_SWITCH; - else if (op2 == 0x0d || op2 == 0x1f) + } else if (op2 == 0x0b || op2 == 0xb9) { + + /* ud2 */ + *type = INSN_BUG; + + } else if (op2 == 0x0d || op2 == 0x1f) { /* nopl/nopw */ *type = INSN_NOP; - else if (op2 == 0xa0 || op2 == 0xa8) { + } else if (op2 == 0xa0 || op2 == 0xa8) { /* push fs/gs */ *type = INSN_STACK; diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 3436a942b606..7578dd9d1148 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -1632,6 +1632,9 @@ static int validate_branch(struct objtool_file *file, struct instruction *first, break; + case INSN_BUG: + return 0; + default: break; } @@ -1693,8 +1696,13 @@ static bool ignore_unreachable_insn(struct instruction *insn) /* * Ignore any unused exceptions. This can happen when a whitelisted * function has an exception table entry. + * + * Also ignore alternative replacement instructions. This can happen + * when a whitelisted function uses one of the ALTERNATIVE macros. */ - if (!strcmp(insn->sec->name, ".fixup")) + if (!strcmp(insn->sec->name, ".fixup") || + !strcmp(insn->sec->name, ".altinstr_replacement") || + !strcmp(insn->sec->name, ".altinstr_aux")) return true; /*