From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751330AbdAWPBG (ORCPT ); Mon, 23 Jan 2017 10:01:06 -0500 Received: from helcar.hengli.com.au ([209.40.204.226]:47013 "EHLO helcar.apana.org.au" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750714AbdAWPBF (ORCPT ); Mon, 23 Jan 2017 10:01:05 -0500 Date: Mon, 23 Jan 2017 23:00:51 +0800 From: Herbert Xu To: Denys Vlasenko Cc: Josh Poimboeuf , Xiaodong Liu , Megha Dey , linux-crypto@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86/crypto: make constants readonly, allow linker to merge them Message-ID: <20170123150051.GG20806@gondor.apana.org.au> References: <20170119213304.18140-1-dvlasenk@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170119213304.18140-1-dvlasenk@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 19, 2017 at 10:33:04PM +0100, Denys Vlasenko wrote: > A lot of asm-optimized routines in arch/x86/crypto/ keep its > constants in .data. This is wrong, they should be on .rodata. > > Mnay of these constants are the same in different modules. > For example, 128-bit shuffle mask 0x000102030405060708090A0B0C0D0E0F > exists in at least half a dozen places. > > There is a way to let linker merge them and use just one copy. > The rules are as follows: mergeable objects of different sizes > should not share sections. You can't put them all in one .rodata > section, they will lose "mergeability". > > GCC puts its mergeable constants in ".rodata.cstSIZE" sections, > or ".rodata.cstSIZE." if -fdata-sections is used. > This patch does the same: > > .section .rodata.cst16.SHUF_MASK, "aM", @progbits, 16 > > It is important that all data in such section consists of > 16-byte elements, not larger ones, and there are no implicit > use of one element from another. > > When this is not the case, use non-mergeable section: > > .section .rodata[.VAR_NAME], "a", @progbits > > This reduces .data by ~15 kbytes: > > text data bss dec hex filename > 11097415 2705840 2630712 16433967 fac32f vmlinux-prev.o > 11112095 2690672 2630712 16433479 fac147 vmlinux.o > > Merged objects are visible in System.map: > > ffffffff81a28810 r POLY > ffffffff81a28810 r POLY > ffffffff81a28820 r TWOONE > ffffffff81a28820 r TWOONE > ffffffff81a28830 r PSHUFFLE_BYTE_FLIP_MASK <- merged regardless of > ffffffff81a28830 r SHUF_MASK <------------- the name difference > ffffffff81a28830 r SHUF_MASK > ffffffff81a28830 r SHUF_MASK > .. > ffffffff81a28d00 r K512 <- merged three identical 640-byte tables > ffffffff81a28d00 r K512 > ffffffff81a28d00 r K512 > > Use of object names in section name suffixes is not strictly necessary, > but might help if someday link stage will use garbage collection > to eliminate unused sections (ld --gc-sections). > > Signed-off-by: Denys Vlasenko Patch applied. Thanks. -- Email: Herbert Xu Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt