Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752145AbbKOA1K (ORCPT ); Sat, 14 Nov 2015 19:27:10 -0500 Received: from ozlabs.org ([103.22.144.67]:41080 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751983AbbKOA1I (ORCPT ); Sat, 14 Nov 2015 19:27:08 -0500 Date: Sun, 15 Nov 2015 11:27:05 +1100 From: Stephen Rothwell To: Michal Marek Cc: linux-next@vger.kernel.org, linux-kernel@vger.kernel.org, Andi Kleen Subject: linux-next: clean up the kbuild tree? Message-ID: <20151115112705.0bf4f0ed@canb.auug.org.au> X-Mailer: Claws Mail 3.13.0 (GTK+ 2.24.28; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6321 Lines: 138 Hi Michal, I notice that the kbuild tree (relative to Linus' tree) only contains lots of merges and these 2 commits from April 2014: commit 19a3cc83353e3bb4bc28769f8606139a3d350d2d Author: Andi Kleen Date: Wed Apr 2 21:49:27 2014 +0200 Kbuild, lto: Add Link Time Optimization support v3 With LTO gcc will do whole program optimizations for the whole kernel and each module. This increases compile time, but can generate faster and smaller code and allows the compiler to do global checking. For example the compiler can complain now about type mismatches for symbols between different files. LTO allows gcc to inline functions between different files and do various other optimization across the whole binary. It might also trigger bugs due to more aggressive optimizations. It allows gcc to drop unused code. It also allows it to check types over the whole program. The compile time is definitely slower. For gcc 4.8 on a typical monolithic config it is about 58% slower. 4.9 drastically improved performance, with slowdown being 38% or so. Also incremenential rebuilds are somewhat slower, as the whole kernel always needs to be reoptimized. Very modular kernels have less build time slow down, as the LTO will run for each module individually. This adds the basic Kbuild plumbing for LTO: - In Kbuild add a new scripts/Makefile.lto that checks the tool chain (note the checks may not be fully bulletproof) and when the tests pass sets the LTO options Currently LTO is very finicky about the tool chain. - 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. - For slim LTO builds (object files containing no backup executable) force AR to gcc-ar - Theoretically LTO should pass through compiler options from the compiler to the link step, but this doesn't work for all options. So the Makefile sets most of these options manually. - Kconfigs: Since LTO with allyesconfig needs more than 4G of memory (~8G) and has the potential to makes people's system swap to death. I used a nested config that ensures that a simple allyesconfig disables LTO. It has to be explicitely enabled. - Some depencies on other Kconfigs: MODVERSIONS, GCOV, FUNCTION_TRACER, KALLSYMS_ALL, single chain WCHAN are incompatible with LTO currently, mostly because they they require setting special compiler options for specific files, which LTO currently doesn't support. MODVERSIONS should in principle work with gcc 4.9, but still disabled. FUNCTION_TRACER/GCOV can be fixed with a unmerged gcc patch. - Also disable strict copy user checks because they trigger errors with LTO. - modpost symbol checking is downgraded to a warning, as in some cases modpost runs before the final link and it cannot resolve LTO symbols at this point. For more information see Documentation/lto-build Thanks to HJ Lu, Joe Mario, Honza Hubicka, Richard Guenther, Don Zickus, Changlong Xie who helped with this project (and probably some more who I forgot, sorry) v2: Merge documentation file into this patch Improve documentation and Kconfig, fix a lot of obsolete comments. Exclude READABLE_ASM Some random fixes v3: Remove CONFIG_LTO_SLIM, is on by default. Signed-off-by: Andi Kleen Signed-off-by: Michal Marek commit 810361b9f65daa6144922ac88087a8426eeae817 Author: Andi Kleen Date: Wed Apr 2 21:49:26 2014 +0200 Kbuild, lto: Set TMPDIR for LTO v4 LTO gcc puts a lot of data into $TMPDIR, essentially another copy of the object directory to pass the repartitioned object files to the code generation processes. TMPDIR defaults to /tmp With /tmp as tmpfs it's easy to drive systems to out of memory, because they will compete with the already high anonymous memory consumption of the wpa LTO pass. When LTO is set always set TMPDIR to the object directory. This could be slightly slower, but is far safer and eliminates another parameter the LTO user would need to set manually. I made it conditional on LTO for now. v2: Allow user to override (H. Peter Anvin) v3: Use standard kernel variable style v4: Print message for redirection (M.Marek) Signed-off-by: Andi Kleen Signed-off-by: Michal Marek Documentation/lto-build | 173 ++++++++++++++++++++ Makefile | 23 ++- arch/x86/Kconfig | 2 +- init/Kconfig | 73 +++++++++ kernel/gcov/Kconfig | 2 +- lib/Kconfig.debug | 2 +- scripts/Makefile.lto | 84 ++++++++++ scripts/Makefile.modpost | 7 +- scripts/coccicheck | 2 +- scripts/coccinelle/free/ifnullfree.cocci | 26 +-- .../iterators/device_node_continue.cocci | 100 ++++++++++++ scripts/coccinelle/misc/compare_const_fl.cocci | 171 ++++++++++++++++++++ scripts/coccinelle/misc/of_table.cocci | 33 +++- scripts/coccinelle/misc/simple_return.cocci | 180 --------------------- scripts/coccinelle/null/deref_null.cocci | 4 +- scripts/coccinelle/tests/odd_ptr_err.cocci | 120 ++++++++++---- scripts/link-vmlinux.sh | 2 +- scripts/package/builddeb | 11 +- scripts/tags.sh | 2 + 19 files changed, 775 insertions(+), 242 deletions(-) -- Cheers, Stephen Rothwell sfr@canb.auug.org.au http://www.canb.auug.org.au/~sfr/ -- 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/