Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751186AbcCFCdy (ORCPT ); Sat, 5 Mar 2016 21:33:54 -0500 Received: from mail-qg0-f53.google.com ([209.85.192.53]:33645 "EHLO mail-qg0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750917AbcCFCdp (ORCPT ); Sat, 5 Mar 2016 21:33:45 -0500 Date: Sat, 5 Mar 2016 21:33:41 -0500 (EST) From: Nicolas Pitre To: Michal Marek cc: linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 5/8] kbuild: add fine grained build dependencies for exported symbols In-Reply-To: <20160305071208.GA25757@pobox.suse.cz> Message-ID: References: <1457070050-1564-1-git-send-email-nicolas.pitre@linaro.org> <1457070050-1564-6-git-send-email-nicolas.pitre@linaro.org> <56DA118E.20106@suse.com> <56DA1201.9010605@suse.cz> <20160305071208.GA25757@pobox.suse.cz> User-Agent: Alpine 2.20 (LFD 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2773 Lines: 54 On Sat, 5 Mar 2016, Michal Marek wrote: > On Fri, Mar 04, 2016 at 11:53:53PM +0100, Michal Marek wrote: > > Dne 4.3.2016 v 23:51 Michal Marek napsal(a): > > > Dne 4.3.2016 v 06:40 Nicolas Pitre napsal(a): > > >> +cmd_and_fixdep = \ > > >> + $(echo-cmd) $(cmd_$(1)); \ > > >> + $(ksym_dep_filter) | \ > > >> + scripts/basic/fixdep -e $(depfile) $@ '$(make-cmd)' \ > > >> + > $(dot-target).tmp; \ > > >> + rm -f $(depfile); \ > > >> + mv -f $(dot-target).tmp $(dot-target).cmd; > > > > > > While trying this, I got a SIGBUS from fixdep once. My theory is that > > > the depfile is mmap()ed by fixdep and modified by the preprocesor run at > > > the same time. I could not reproduce this so far (still trying). But if > > > it's really this race, the fix would be to disable dependency generation > > > in the preprocessor by passing -Wp,MD,/dev/null or somesuch. But we > > > never had this problem with genksyms, which is weird. It could as well > > > be that my build machine's memory is faulty :(. > > > > Actually, genksyms does not ran in parallel. neither before nor after > run > > this patch. > > I reproduced the SIGBUS after a few iterations, and it crashes in > parse_dep_file(). I'm now testing this > > diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include > index 0be7e09ba381..4fdd8348acf6 100644 > --- a/scripts/Kbuild.include > +++ b/scripts/Kbuild.include > @@ -270,10 +270,12 @@ else > > # Filter out exported kernel symbol names from the preprocessor output. > # See also __KSYM_DEPS__ in include/linux/export.h. > +# We disable the depfile generation here, so as not to overwrite the existing > +# depfile while fixdep is parsing it > ksym_dep_filter = \ > case "$(1)" in \ > - cc_*_c) $(CPP) $(c_flags) -D__KSYM_DEPS__ $< ;; \ > - as_*_S) $(CPP) $(a_flags) -D__KSYM_DEPS__ $< ;; \ > + cc_*_c) $(CPP) $(filter-out -Wp$(comma)-M%, $(c_flags)) -D__KSYM_DEPS__ $< ;; \ > + as_*_S) $(CPP) $(filter-out -Wp$(comma)-M%, $(a_flags)) -D__KSYM_DEPS__ $< ;; \ > cpp_lds_S) : ;; \ > *) echo "Don't know how to preprocess $(1)"; false ;; \ > esac | sed -rn 's/^.*=== __KSYM_(.*) ===.*$$/KSYM_\1/p' This makes perfect sense even if I can't reproduce on my side. Are you willing to fold this patch in, or do you prefer that I repost? Nicolas