From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga07.intel.com ([134.134.136.100]:50222 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751404AbeA0A4E (ORCPT ); Fri, 26 Jan 2018 19:56:04 -0500 Date: Fri, 26 Jan 2018 16:55:54 -0800 From: Andi Kleen Subject: Re: [PATCH 20/21] Kbuild, lto: Add Link Time Optimization support Message-ID: <20180127005554.GM26209@tassilo.jf.intel.com> References: <20171127213423.27218-1-andi@firstfloor.org> <20171127213423.27218-21-andi@firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kbuild-owner@vger.kernel.org List-ID: To: Arnd Bergmann Cc: Andi Kleen , Linux Kernel Mailing List , the arch/x86 maintainers , samitolvanen@google.com, alxmtvv@gmail.com, Linux Kbuild mailing list , Masahiro Yamada , Andrew Morton On Sat, Jan 27, 2018 at 01:15:49AM +0100, Arnd Bergmann wrote: > On Mon, Nov 27, 2017 at 10:34 PM, Andi Kleen wrote: > > From: Andi Kleen > > - Add a new LDFINAL variable that controls the final link > > for vmlinux or module. In this case we call gcc-ld instead > > of ld, to run the LTO step. > > When I tried this out on allmodconfig (following the lwn article), I ran into > a number of warnings: Thanks for testing. Yes it's a known issue: during one module build when modpost looks at the file it is still in LTO format, and modpost doesn't understand the LTO symbol table. I had a patch to teach it to it at some point, but it got lost somewhere. The LLVM LTO patchkit has a different solution that actually fixes the sequence to run modpost only after a LTO final link, but I haven't gotten around to port that one. It seems to work already for the single file modules. -Andi