From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: stack validation warning on lttng-modules bytecode interpreter Date: Wed, 15 Jun 2016 16:55:16 +0000 (UTC) Message-ID: <1074038231.37468.1466009716273.JavaMail.zimbra@efficios.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: Sender: linux-kernel-owner@vger.kernel.org To: Josh Poimboeuf Cc: lttng-dev , Linux Kernel Mailing List List-Id: lttng-dev@lists.lttng.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