From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932706AbcFOQzZ (ORCPT ); Wed, 15 Jun 2016 12:55:25 -0400 Received: from mail.efficios.com ([78.47.125.74]:41777 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752578AbcFOQzW (ORCPT ); Wed, 15 Jun 2016 12:55:22 -0400 Date: Wed, 15 Jun 2016 16:55:16 +0000 (UTC) From: Mathieu Desnoyers To: Josh Poimboeuf Cc: lttng-dev , Linux Kernel Mailing List Message-ID: <1074038231.37468.1466009716273.JavaMail.zimbra@efficios.com> Subject: stack validation warning on lttng-modules bytecode interpreter MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [78.47.125.74] X-Mailer: Zimbra 8.6.0_GA_1178 (ZimbraWebClient - FF45 (Linux)/8.6.0_GA_1178) Thread-Topic: stack validation warning on lttng-modules bytecode interpreter Thread-Index: jOxCaYm/4ELYQ5dWHInh4w+qtG9VxA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Josh, I notice that with gcc 6.1.1, kernel 4.6, with CONFIG_STACK_VALIDATION=y, building lttng-modules master at commit 6c09dd94 gives this warning: lttng-modules/lttng-filter-interpreter.o: warning: objtool: lttng_filter_interpret_bytecode()+0x58: sibling call from callable instruction with changed frame pointer this object implements a bytecode interpreter using an explicit jump table (see https://github.com/lttng/lttng-modules/blob/master/lttng-filter-interpreter.c) If I define "INTERPRETER_USE_SWITCH" at the top of the file, thus using the switch-case fallback implementation, the warning vanishes. We use an explicit jump table rather than a switch case whenever possible for performance reasons. I notice that tools/objtool/builtin-check.c needs to be aware of switch-cases transformed into jump tables by the compiler. Are explicit jump tables supported by the stack validator ? Do we need to add annotation to our code ? Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com