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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 54F22C282DF for ; Fri, 19 Apr 2019 20:08:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 23C91217F9 for ; Fri, 19 Apr 2019 20:08:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1555704511; bh=C+p1NL8mFdhSCUqYHh0ol748ybYOAWTd11xT8WF9pRM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=Dt/4PyZVfhLgb/XVNLjg9iRaxHR2dy92JLjwg9sQ9YCOewC/9sW6mTZGT5EBXPoTx hwskOqdSMlfO+XuHCsNCsiv5EwnOswYDfpX/b79WGggPCWpbE1rSmAUI33HWsYlU3y QqPXC4zs8U9YFcPyNUvfGCcybibno6EVVinfZDR0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728162AbfDSUIa (ORCPT ); Fri, 19 Apr 2019 16:08:30 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:56766 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726187AbfDSUI3 (ORCPT ); Fri, 19 Apr 2019 16:08:29 -0400 Received: from localhost.localdomain (c-73-223-200-170.hsd1.ca.comcast.net [73.223.200.170]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id A0A0F27C6; Fri, 19 Apr 2019 20:08:28 +0000 (UTC) Date: Fri, 19 Apr 2019 13:08:26 -0700 From: Andrew Morton To: Alexey Dobriyan Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH -mm] elf: init pt_regs pointer later Message-Id: <20190419130826.849441bb8f526c9defcb1c0f@linux-foundation.org> In-Reply-To: <20190419200343.GA19788@avx2> References: <20190419200343.GA19788@avx2> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 19 Apr 2019 23:03:43 +0300 Alexey Dobriyan wrote: > Get "current_pt_regs" pointer right before usage. > > Space savings on x86_64: > > add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-180 (-180) > Function old new delta > load_elf_binary 5806 5626 -180 !!! -256 bytes with my setup. > --- a/fs/binfmt_elf.c > +++ b/fs/binfmt_elf.c > @@ -704,12 +704,12 @@ static int load_elf_binary(struct linux_binprm *bprm) > unsigned long start_code, end_code, start_data, end_data; > unsigned long reloc_func_desc __maybe_unused = 0; > int executable_stack = EXSTACK_DEFAULT; > - struct pt_regs *regs = current_pt_regs(); > struct { > struct elfhdr elf_ex; > struct elfhdr interp_elf_ex; > } *loc; > struct arch_elf_state arch_state = INIT_ARCH_ELF_STATE; > + struct pt_regs *regs; > > loc = kmalloc(sizeof(*loc), GFP_KERNEL); > if (!loc) { > @@ -1159,6 +1159,7 @@ static int load_elf_binary(struct linux_binprm *bprm) > MAP_FIXED | MAP_PRIVATE, 0); > } > > + regs = current_pt_regs(); > #ifdef ELF_PLAT_INIT > /* > * The ABI may specify that certain registers be set up in special Why the heck does this make such a difference?