From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [RFC][PATCH] objtool,x86_64: Replace recordmcount with objtool Date: Fri, 26 Jun 2020 13:29:31 +0200 Message-ID: <20200626112931.GF4817@hirez.programming.kicks-ass.net> References: <20200624203200.78870-1-samitolvanen@google.com> <20200624203200.78870-5-samitolvanen@google.com> <20200624212737.GV4817@hirez.programming.kicks-ass.net> <20200624214530.GA120457@google.com> <20200625074530.GW4817@hirez.programming.kicks-ass.net> <20200625161503.GB173089@google.com> <20200625200235.GQ4781@hirez.programming.kicks-ass.net> <20200625224042.GA169781@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Content-Disposition: inline In-Reply-To: <20200625224042.GA169781@google.com> To: Sami Tolvanen Cc: Steven Rostedt , Masahiro Yamada , Will Deacon , Greg Kroah-Hartman , "Paul E. McKenney" , Kees Cook , Nick Desaulniers , clang-built-linux@googlegroups.com, kernel-hardening@lists.openwall.com, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, x86@kernel.org, Josh Poimboeuf , mhelsley@vmware.com List-Id: linux-arch.vger.kernel.org On Thu, Jun 25, 2020 at 03:40:42PM -0700, Sami Tolvanen wrote: > > Not boot tested, but it generates the required sections and they look > > more or less as expected, ymmv. > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > > index a291823f3f26..189575c12434 100644 > > --- a/arch/x86/Kconfig > > +++ b/arch/x86/Kconfig > > @@ -174,7 +174,6 @@ config X86 > > select HAVE_EXIT_THREAD > > select HAVE_FAST_GUP > > select HAVE_FENTRY if X86_64 || DYNAMIC_FTRACE > > - select HAVE_FTRACE_MCOUNT_RECORD > > select HAVE_FUNCTION_GRAPH_TRACER > > select HAVE_FUNCTION_TRACER > > select HAVE_GCC_PLUGINS > > This breaks DYNAMIC_FTRACE according to kernel/trace/ftrace.c: > > #ifndef CONFIG_FTRACE_MCOUNT_RECORD > # error Dynamic ftrace depends on MCOUNT_RECORD > #endif > > And the build errors after that seem to confirm this. It looks like we might > need another flag to skip recordmcount. Hurm, Steve, how you want to do that? > Anyway, since objtool is run before recordmcount, I just left this unchanged > for testing and ignored the recordmcount warnings about __mcount_loc already > existing. Something is a bit off still though, I see this at boot: > > ------------[ ftrace bug ]------------ > ftrace failed to modify > [] __tracepoint_iter_initcall_level+0x0/0x40 > actual: 0f:1f:44:00:00 > Initializing ftrace call sites > ftrace record flags: 0 > (0) > expected tramp: ffffffff81056500 > ------------[ cut here ]------------ > > Otherwise, this looks pretty good. Ha! it is trying to convert the "CALL __fentry__" into a NOP and not finding the CALL -- because objtool already made it a NOP... Weird, I thought recordmcount would also write NOPs, it certainly has code for that. I suppose we can use CC_USING_NOP_MCOUNT to avoid those, but I'd rather Steve explain this before I wreck things further. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43920 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728467AbgFZLaU (ORCPT ); Fri, 26 Jun 2020 07:30:20 -0400 Date: Fri, 26 Jun 2020 13:29:31 +0200 From: Peter Zijlstra Subject: Re: [RFC][PATCH] objtool,x86_64: Replace recordmcount with objtool Message-ID: <20200626112931.GF4817@hirez.programming.kicks-ass.net> References: <20200624203200.78870-1-samitolvanen@google.com> <20200624203200.78870-5-samitolvanen@google.com> <20200624212737.GV4817@hirez.programming.kicks-ass.net> <20200624214530.GA120457@google.com> <20200625074530.GW4817@hirez.programming.kicks-ass.net> <20200625161503.GB173089@google.com> <20200625200235.GQ4781@hirez.programming.kicks-ass.net> <20200625224042.GA169781@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200625224042.GA169781@google.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Sami Tolvanen Cc: Steven Rostedt , Masahiro Yamada , Will Deacon , Greg Kroah-Hartman , "Paul E. McKenney" , Kees Cook , Nick Desaulniers , clang-built-linux@googlegroups.com, kernel-hardening@lists.openwall.com, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, x86@kernel.org, Josh Poimboeuf , mhelsley@vmware.com Message-ID: <20200626112931.fSIoncvVhsw_np_gVdynRz_YMjFEPLQErT2HHXvZHiU@z> On Thu, Jun 25, 2020 at 03:40:42PM -0700, Sami Tolvanen wrote: > > Not boot tested, but it generates the required sections and they look > > more or less as expected, ymmv. > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > > index a291823f3f26..189575c12434 100644 > > --- a/arch/x86/Kconfig > > +++ b/arch/x86/Kconfig > > @@ -174,7 +174,6 @@ config X86 > > select HAVE_EXIT_THREAD > > select HAVE_FAST_GUP > > select HAVE_FENTRY if X86_64 || DYNAMIC_FTRACE > > - select HAVE_FTRACE_MCOUNT_RECORD > > select HAVE_FUNCTION_GRAPH_TRACER > > select HAVE_FUNCTION_TRACER > > select HAVE_GCC_PLUGINS > > This breaks DYNAMIC_FTRACE according to kernel/trace/ftrace.c: > > #ifndef CONFIG_FTRACE_MCOUNT_RECORD > # error Dynamic ftrace depends on MCOUNT_RECORD > #endif > > And the build errors after that seem to confirm this. It looks like we might > need another flag to skip recordmcount. Hurm, Steve, how you want to do that? > Anyway, since objtool is run before recordmcount, I just left this unchanged > for testing and ignored the recordmcount warnings about __mcount_loc already > existing. Something is a bit off still though, I see this at boot: > > ------------[ ftrace bug ]------------ > ftrace failed to modify > [] __tracepoint_iter_initcall_level+0x0/0x40 > actual: 0f:1f:44:00:00 > Initializing ftrace call sites > ftrace record flags: 0 > (0) > expected tramp: ffffffff81056500 > ------------[ cut here ]------------ > > Otherwise, this looks pretty good. Ha! it is trying to convert the "CALL __fentry__" into a NOP and not finding the CALL -- because objtool already made it a NOP... Weird, I thought recordmcount would also write NOPs, it certainly has code for that. I suppose we can use CC_USING_NOP_MCOUNT to avoid those, but I'd rather Steve explain this before I wreck things further.