Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755020AbbDXMkH (ORCPT ); Fri, 24 Apr 2015 08:40:07 -0400 Received: from mail-oi0-f44.google.com ([209.85.218.44]:35682 "EHLO mail-oi0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754440AbbDXMkE convert rfc822-to-8bit (ORCPT ); Fri, 24 Apr 2015 08:40:04 -0400 MIME-Version: 1.0 In-Reply-To: <1429824329-40690-1-git-send-email-fche@redhat.com> References: <1416595200-22359-1-git-send-email-jistone@redhat.com> <1429824329-40690-1-git-send-email-fche@redhat.com> Date: Fri, 24 Apr 2015 08:40:02 -0400 X-Google-Sender-Auth: 3yTAg9nqSYiHh9lLCnXIyEwTou4 Message-ID: Subject: Re: [PATCH] Kbuild: Add an option to enable GCC VTA From: Josh Boyer To: "Frank Ch. Eigler" Cc: "Linux-Kernel@Vger. Kernel. Org" , Josh Stone , Jakub Jelinek , Greg Kroah-Hartman , Linus Torvalds , Andrew Morton , Markus Trippelsdorf , =?ISO-8859-1?Q?Michel_D=E4nzer?= Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3196 Lines: 78 On Thu, Apr 23, 2015 at 5:25 PM, Frank Ch. Eigler wrote: > From: Josh Stone > > Due to isolated gcc codegen issues, gcc -fvar-tracking-assignments > was unconditionally disabled in commit 2062afb4f804 ("Fix gcc-4.9.0 > miscompilation of load_balance() in scheduler"). > > However, this reduces the debuginfo coverage for variable locations, > especially in inline functions. VTA is certainly not perfect either > in those cases, but it is much better than without. With compiler > versions that have fixed the codegen bugs, we would prefer to have the > better details for SystemTap, and surely other debuginfo consumers > like perf will benefit as well. > > This patch simply makes CONFIG_DEBUG_INFO_VTA an option. I considered > Frank and Linus's discussion of a cc-option-like -fcompare-debug test, > but I'm convinced that a narrow test of an arch-specific codegen issue > is not really useful. GCC has their own regression tests for this, so > I'd suggest GCC_COMPARE_DEBUG=-fvar-tracking-assignments-toggle is more > useful for kernel developers to test confidence. > > In fact, I ran into a couple more issues when testing for this patch[1], > although neither of those had any codegen impact. > [1] https://bugzilla.redhat.com/show_bug.cgi?id=1140872 > > With gcc-4.9.2-1.fc22, I can now build v3.18-rc5 with Fedora's i686 and > x86_64 configs, and this is completely clean with GCC_COMPARE_DEBUG. > > Cc: Jakub Jelinek > Cc: Josh Boyer > Cc: Greg Kroah-Hartman > Cc: Linus Torvalds > Cc: Andrew Morton > Cc: Markus Trippelsdorf > Cc: Michel D?nzer > Signed-off-by: Josh Stone > Signed-off-by: Frank Ch. Eigler Frank, did you rebase this against some newer tree or something? Curious why you sent it again. > Makefile | 8 ++++++-- > lib/Kconfig.debug | 21 ++++++++++++++++++++- > 2 files changed, 26 insertions(+), 3 deletions(-) > > diff --git a/Makefile b/Makefile > index 6cc5b2434224..c8e1fcfdb41a 100644 > --- a/Makefile > +++ b/Makefile > @@ -704,8 +704,6 @@ KBUILD_CFLAGS += -fomit-frame-pointer > endif > endif > > -KBUILD_CFLAGS += $(call cc-option, -fno-var-tracking-assignments) > - > ifdef CONFIG_DEBUG_INFO > ifdef CONFIG_DEBUG_INFO_SPLIT > KBUILD_CFLAGS += $(call cc-option, -gsplit-dwarf, -g) > @@ -718,6 +716,12 @@ ifdef CONFIG_DEBUG_INFO_DWARF4 > KBUILD_CFLAGS += $(call cc-option, -gdwarf-4,) > endif > > +ifdef CONFIG_DEBUG_INFO_VTA > +KBUILD_CFLAGS += $(call cc-option, -fvar-tracking-assignments) > +else > +KBUILD_CFLAGS += $(call cc-option, -fno-var-tracking-assignments) > +endif > + Is there a reason you moved this hunk under the DWARF4 options instead of modifying it in-place like the original patch did? josh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/