From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 61469C432BE for ; Wed, 18 Aug 2021 02:34:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3F71C61056 for ; Wed, 18 Aug 2021 02:34:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236860AbhHRCfW (ORCPT ); Tue, 17 Aug 2021 22:35:22 -0400 Received: from conssluserg-04.nifty.com ([210.131.2.83]:53389 "EHLO conssluserg-04.nifty.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235464AbhHRCfU (ORCPT ); Tue, 17 Aug 2021 22:35:20 -0400 Received: from mail-pf1-f180.google.com (mail-pf1-f180.google.com [209.85.210.180]) (authenticated) by conssluserg-04.nifty.com with ESMTP id 17I2YKKh030317; Wed, 18 Aug 2021 11:34:20 +0900 DKIM-Filter: OpenDKIM Filter v2.10.3 conssluserg-04.nifty.com 17I2YKKh030317 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nifty.com; s=dec2015msa; t=1629254060; bh=tSrtc1Fo6BTES2NTrunR7VHJaBchrQC+4v/A753o6u4=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=KseHonVk1PAeD+2DVeiGZN9kt976s4Hetk4gPMW9LKLoEiFXqDWtjARCL/x1usvzh pUpTKSb0gM7SEZ4MWqAy+13aP54D6cK7WwyvkOUmp/67/GgZJfJLBq7EsDm1rfONBX s5gjMgoE6NA7RFI0G65NCUFcomoIuiuDowyYWaAM2fVLiVApIqWlgoXj2CD3a7c0P7 O5P/Rjkc0GDBgyG+m0Y2iV4IcpkkoBh+65Xd06ytuDo7S1XYW3VTSdIxmvCt3rpsvD XA32+TAnMMhps0YxmUsDLruySgqFSswC2mzOME9cowZi5LhzIm1TGhf/M7LpYpM1wc 75oMJdGy2iytg== X-Nifty-SrcIP: [209.85.210.180] Received: by mail-pf1-f180.google.com with SMTP id a21so656701pfh.5; Tue, 17 Aug 2021 19:34:20 -0700 (PDT) X-Gm-Message-State: AOAM5306G9iDV/m+8uV6LEwZ5LdEIMtBDbxOvgqdUQM/FXvso6f7TS6S P+DqF/rfW2MbRBqe4+eckQ56kKuwEPv+P3YBUnI= X-Google-Smtp-Source: ABdhPJwBHodEUpjXcVpwPs2tREgkr0VLZPBxe5MPj8qkKS95sxf+EypEr/EHKEkfFNPij57GqQ4CjUioPpPTacWQx9Q= X-Received: by 2002:aa7:94ac:0:b0:3e0:f21a:e6ff with SMTP id a12-20020aa794ac000000b003e0f21ae6ffmr6607968pfl.76.1629254059709; Tue, 17 Aug 2021 19:34:19 -0700 (PDT) MIME-Version: 1.0 References: <20210816180519.1021311-1-samitolvanen@google.com> In-Reply-To: <20210816180519.1021311-1-samitolvanen@google.com> From: Masahiro Yamada Date: Wed, 18 Aug 2021 11:33:43 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v4] kbuild: Fix TRIM_UNUSED_KSYMS with LTO_CLANG To: Sami Tolvanen Cc: Kees Cook , Michal Marek , Alexander Lobakin , Nathan Chancellor , Nick Desaulniers , Linux Kbuild mailing list , clang-built-linux , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 17, 2021 at 3:05 AM Sami Tolvanen wrote: > > With CONFIG_LTO_CLANG, we currently link modules into native > code just before modpost, which means with TRIM_UNUSED_KSYMS > enabled, we still look at the LLVM bitcode in the .o files when > generating the list of used symbols. As the bitcode doesn't > yet have calls to compiler intrinsics and llvm-nm doesn't see > function references that only exist in function-level inline > assembly, we currently need a whitelist for TRIM_UNUSED_KSYMS to > work with LTO. > > This change moves module LTO linking to happen earlier, and > thus avoids the issue with LLVM bitcode and TRIM_UNUSED_KSYMS > entirely, allowing us to also drop the whitelist from > gen_autoksyms.sh. > > Link: https://github.com/ClangBuiltLinux/linux/issues/1369 > Signed-off-by: Sami Tolvanen > Reviewed-by: Alexander Lobakin > Tested-by: Alexander Lobakin > --- > Changes in v4: > - Added .lto.o to targets to actually fix the use of if_changed. > - Replaced an unnecessary mod-prelink-ext with .lto. > > Changes in v3: > - Added missing FORCE. > > Changes in v2: > - Fixed a couple of typos. > - Fixed objtool arguments for .lto.o to always include --module. > > --- > scripts/Makefile.build | 28 +++++++++++++++++++++++++++- > scripts/Makefile.lib | 7 +++++++ > scripts/Makefile.modfinal | 21 ++------------------- > scripts/Makefile.modpost | 22 +++------------------- > scripts/gen_autoksyms.sh | 12 ------------ > 5 files changed, 39 insertions(+), 51 deletions(-) > > diff --git a/scripts/Makefile.build b/scripts/Makefile.build > index 02197cb8e3a7..a6f43afd09bb 100644 > --- a/scripts/Makefile.build > +++ b/scripts/Makefile.build > @@ -88,6 +88,10 @@ endif > > targets-for-modules := $(patsubst %.o, %.mod, $(filter %.o, $(obj-m))) > > +ifdef CONFIG_LTO_CLANG > +targets-for-modules += $(patsubst %.o, %.lto.o, $(filter %.o, $(obj-m))) > +endif > + > ifdef need-modorder > targets-for-modules += $(obj)/modules.order > endif > @@ -271,12 +275,34 @@ $(obj)/%.o: $(src)/%.c $(recordmcount_source) $$(objtool_dep) FORCE > $(call if_changed_rule,cc_o_c) > $(call cmd,force_checksrc) > > +ifdef CONFIG_LTO_CLANG > +# Module .o files may contain LLVM bitcode, compile them into native code > +# before ELF processing > +quiet_cmd_cc_lto_link_modules = LTO [M] $@ > +cmd_cc_lto_link_modules = \ > + $(LD) $(ld_flags) -r -o $@ \ > + $(shell [ -s $(@:.lto.o=.o.symversions) ] && \ > + echo -T $(@:.lto.o=.o.symversions)) \ > + --whole-archive $(filter-out FORCE,$^) > + > +ifdef CONFIG_STACK_VALIDATION > +# objtool was skipped for LLVM bitcode, run it now that we have compiled > +# modules into native code > +cmd_cc_lto_link_modules += ; \ > + $(objtree)/tools/objtool/objtool $(objtool_args) --module \ > + $(@:.ko=.lto.o) What is this "$(@:.ko=.lto.o)" doing ? The target is already suffixed with .lto.o so $(@:.ko=.lto.o) should be the same as $@ Shall I fix it locally unless I find more questionable code? > +endif > + > +$(obj)/%.lto.o: $(obj)/%.o FORCE > + $(call if_changed,cc_lto_link_modules) > +endif > + -- Best Regards Masahiro Yamada