From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933091AbbGGW7l (ORCPT ); Tue, 7 Jul 2015 18:59:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53159 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752614AbbGGW7e (ORCPT ); Tue, 7 Jul 2015 18:59:34 -0400 Date: Tue, 7 Jul 2015 17:59:31 -0500 From: Josh Poimboeuf To: Andy Lutomirski Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Michal Marek , Peter Zijlstra , Andy Lutomirski , Borislav Petkov , Linus Torvalds , Andi Kleen , Pedro Alves , X86 ML , live-patching@vger.kernel.org, "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v6 4/4] stackvalidate: Add ignore macros Message-ID: <20150707225931.GB31294@treble.redhat.com> References: <30c25e5414ca777fef3b6c189b26b34a290b12f9.1436280380.git.jpoimboe@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 07, 2015 at 03:00:38PM -0700, Andy Lutomirski wrote: > On Tue, Jul 7, 2015 at 7:54 AM, Josh Poimboeuf wrote: > > Add new stackvalidate ignore macros: STACKVALIDATE_IGNORE_INSN and > > STACKVALIDATE_IGNORE_FUNC. These can be used to tell stackvalidate to > > skip validation of an instruction or a function, respectively. > > > > Signed-off-by: Josh Poimboeuf > > --- > > include/linux/stackvalidate.h | 38 ++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 38 insertions(+) > > create mode 100644 include/linux/stackvalidate.h > > > > diff --git a/include/linux/stackvalidate.h b/include/linux/stackvalidate.h > > new file mode 100644 > > index 0000000..30d4a60 > > --- /dev/null > > +++ b/include/linux/stackvalidate.h > > @@ -0,0 +1,38 @@ > > +#ifndef _LINUX_STACKVALIDATE_H > > +#define _LINUX_STACKVALIDATE_H > > + > > +#ifndef __ASSEMBLY__ > > + > > +/* > > + * This C macro tells the stack validation script to ignore the function. It > > + * should only be used in special cases where you're 100% sure it won't affect > > + * the reliability of frame pointers and kernel stack traces. > > + * > > + * For more information, see Documentation/stack-validation.txt. > > + */ > > +#define STACKVALIDATE_IGNORE_FUNC(_func) \ > > + void __attribute__((section("__stackvalidate_ignore_func,\"ae\"#"))) \ > > + *__stackvalidate_ignore_func_##_func = _func > > + > > static? Otherwise there's some risk that ignoring a static function > will cause a duplicate symbol. Alternatively you could generate a > more unique name. > > Also, should the linker script be updated to discard this section? It validates per individual object file, so there shouldn't be a risk of duplicate symbols. The 'e' flag in ,\"ae\"#" tells the linker to discard the section. (The ,\"ae\"# stuff is a horrible hack, but it's the only way I could figure out how to set the section flags from C code. The '#' is used to comment out gcc's default arguments to the .section directive in favor of the "ae" flags.) > > +#else /* __ASSEMBLY__ */ > > + > > +/* > > + * This asm macro tells the stack validation script to ignore the instruction > > + * immediately after the macro. It should only be used in special cases where > > + * you're 100% sure it won't affect the reliability of frame pointers and > > + * kernel stack traces. > > + * > > + * For more information, see Documentation/stack-validation.txt. > > + */ > > +.macro STACKVALIDATE_IGNORE_INSN > > + .if CONFIG_STACK_VALIDATION > > + 163: > > Some day we should come up with a better way to do this than using a > random three-digit number. I wonder if something like .Ltemp_\@ could > be used for this purpose. Agreed. And .Ltemp_\@ sounds like a good idea. I'll try it. -- Josh