From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from conssluserg-05.nifty.com (conssluserg-05.nifty.com [210.131.2.90]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 608467B for ; Thu, 28 Apr 2022 04:39:53 +0000 (UTC) Received: from mail-pj1-f41.google.com (mail-pj1-f41.google.com [209.85.216.41]) (authenticated) by conssluserg-05.nifty.com with ESMTP id 23S4dh1b005559 for ; Thu, 28 Apr 2022 13:39:43 +0900 DKIM-Filter: OpenDKIM Filter v2.10.3 conssluserg-05.nifty.com 23S4dh1b005559 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nifty.com; s=dec2015msa; t=1651120783; bh=iBbx4Um+YnFgBw9+6W5xvHjA6yLfdqlZz4cqEJPhD8I=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=1WRIMiGSKmIg9XQwPj++zo4qllaXuXZDmIJYLFdu4BgyOxlVuywgU7Vp/1S534IJj MzMcpVc7fePsMiz0E5vBpBa3nlkJXrXSywAK+2OzQx0oBj5kORUWFr0tf1KtocmtlK iY6cXT5TQcse0AxeRivssctYrkgiM3TCgqppiavZ46Jw3fP7SW7t6Jl3mNci4d72g3 hwaf7V06lJZZqlVjTMiisOgU6CdMXWjKFVP0501FdiBXX4f2L3zKt1vrp67g8xQQ2v HEpotsQWNPuIdKszSHBSojT2hQjpvQUFXozy2BKfu00c+b/FMM6zVOELphA1VNVedS oOkYeIKUJogqQ== X-Nifty-SrcIP: [209.85.216.41] Received: by mail-pj1-f41.google.com with SMTP id fv2so3234420pjb.4 for ; Wed, 27 Apr 2022 21:39:43 -0700 (PDT) X-Gm-Message-State: AOAM533RBPAnrLmlCxnDaP6c2RndK/xNOTHOkFD6PDbtc38CJ7RvB8y+ 7lVjSeTcks22PdvJoLyvImwI814twUdXO7IDwyY= X-Google-Smtp-Source: ABdhPJyZut0COx0/akB+Az14gk+5DsF9HH/uKj/hWC5PO6CN6TzA2wK5ynNKB2HNbQseIzREsbBNHNHPxWVVUQiDXMA= X-Received: by 2002:a17:902:bf07:b0:158:d334:852f with SMTP id bi7-20020a170902bf0700b00158d334852fmr31840136plb.136.1651120782642; Wed, 27 Apr 2022 21:39:42 -0700 (PDT) Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20220424190811.1678416-1-masahiroy@kernel.org> <20220424190811.1678416-28-masahiroy@kernel.org> In-Reply-To: From: Masahiro Yamada Date: Thu, 28 Apr 2022 13:38:39 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 27/27] kbuild: do not create *.prelink.o for Clang LTO or IBT To: Nicolas Schier Cc: Linux Kbuild mailing list , Linux Kernel Mailing List , Michal Marek , Nathan Chancellor , Nick Desaulniers , clang-built-linux Content-Type: text/plain; charset="UTF-8" On Thu, Apr 28, 2022 at 12:31 PM Nicolas Schier wrote: > > On Mon 25 Apr 2022 04:08:11 GMT Masahiro Yamada wrote: > > When CONFIG_LTO_CLANG=y, additional intermediate *.prelink.o is > > created > > for each module. Also, objtool is postponed until LLVM bitcode is > > converted to ELF. > > > > CONFIG_X86_KERNEL_IBT works in a similar way to postpone objtool until > > objects are merged together. > > > > This commit stops generating *.prelink.o, so the build flow will look > > the same with/without LTO. > > > > The following figures show how the LTO build currently works, and > > how this commit is changing it. > > > > Current build flow > > ================== > > > > [1] single-object module > > > > [+objtool] > > $(CC) $(LD) $(LD) > > foo.c --------------------> foo.o -----> foo.prelink.o -----> foo.ko > > (LLVM bitcode) (ELF) | > > | > > foo.mod.o --/ > > > > [2] multi-object module > > [+objtool] > > $(CC) $(AR) $(LD) $(LD) > > foo1.c -----> foo1.o -----> foo.o -----> foo.prelink.o -----> foo.ko > > | (archive) (ELF) | > > foo2.c -----> foo2.o --/ | > > (LLVM bitcode) foo.mod.o --/ > > > > One confusion is foo.o in multi-object module is an archive despite of > > its suffix. > > > > New build flow > > ============== > > > > [1] single-object module > > > > Since there is only one object, we do not need to have the LLVM > > bitcode stage. Use $(CC)+$(LD) to generate an ELF object in one > > build rule. Of course, only $(CC) is used when LTO is disabled. > > > > $(CC)+$(LD)[+objtool] $(LD) > > foo.c ------------------------> foo.o -------> foo.ko > > (ELF) | > > | > > foo.mod.o --/ > > > > [2] multi-object module > > > > Previously, $(AR) was used to combine LLVM bitcode into an archive, > > but there was not a technical reason to do so. > > This commit just uses $(LD) to combine and convert them into a single > > ELF object. > > > > [+objtool] > > $(CC) $(LD) $(LD) > > foo1.c -------> foo1.o -------> foo.o -------> foo.ko > > | (ELF) | > > foo2.c -------> foo2.o ---/ | > > (LLVM bitcode) foo.mod.o --/ > > > > Signed-off-by: Masahiro Yamada > > --- > > > > scripts/Kbuild.include | 4 +++ > > scripts/Makefile.build | 58 ++++++++++++--------------------------- > > scripts/Makefile.lib | 7 ----- > > scripts/Makefile.modfinal | 5 ++-- > > scripts/Makefile.modpost | 9 ++---- > > scripts/mod/modpost.c | 7 ----- > > 6 files changed, 25 insertions(+), 65 deletions(-) > > > > diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include > > index 3514c2149e9d..455a0a6ce12d 100644 > > --- a/scripts/Kbuild.include > > +++ b/scripts/Kbuild.include > > @@ -15,6 +15,10 @@ pound := \# > > # Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o > > dot-target = $(dir $@).$(notdir $@) > > > > +### > > +# Name of target with a '.tmp_' as filename prefix. foo/bar.o => foo/.tmp_bar.o > > +tmp-target = $(dir $@).tmp_$(notdir $@) > > This matches the dot-target definition above, otherwise $(@D).tmp_$(@F) > would be an alternative. Yes, I intentionally made dot-target and tmp-target look similar. The difference is $(dir ...) leaves the trailing slash, but $(@D) does not. The alternative would be $(@D)/.tmp_$(@F) > > > + > > ### > > # The temporary file to save gcc -MMD generated dependencies must not > > # contain a comma > > diff --git a/scripts/Makefile.build b/scripts/Makefile.build > > index 7f199b0a5170..fe4d3a908dd0 100644 > > --- a/scripts/Makefile.build > > +++ b/scripts/Makefile.build > > @@ -88,10 +88,6 @@ endif > > targets-for-modules := $(foreach x, o mod $(if $(CONFIG_TRIM_UNUSED_KSYMS), usyms), \ > > $(patsubst %.o, %.$x, $(filter %.o, $(obj-m)))) > > > > -ifneq ($(CONFIG_LTO_CLANG)$(CONFIG_X86_KERNEL_IBT),) > > -targets-for-modules += $(patsubst %.o, %.prelink.o, $(filter %.o, $(obj-m))) > > -endif > > - > > ifdef need-modorder > > targets-for-modules += $(obj)/modules.order > > endif > > @@ -153,8 +149,16 @@ $(obj)/%.ll: $(src)/%.c FORCE > > # The C file is compiled and updated dependency information is generated. > > # (See cmd_cc_o_c + relevant part of rule_cc_o_c) > > > > +is-single-obj-m = $(if $(part-of-module),$(if $(filter $@, $(obj-m)),y)) > > Perhaps using $(and ..,..,y) instead if $(if ..,$(if ..,y))? Good idea! I did not notice this. I will do it in v2. > > > > -endif > > +delay-objtool := $(or $(CONFIG_LTO_CLANG),$(CONFIG_X86_KERNEL_IBT)) > > + > > +$(obj)/%.o: objtool-enabled = $(if $(is-standard-object),$(if $(delay-objtool),$(is-single-obj-m),y)) > > same here? $(and) versus $(if ..,$(if ..,y)) I am not sure about this case. The second if-func is $(if cond, A, B) form. -- Best Regards Masahiro Yamada