From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932521AbcLGPYi (ORCPT ); Wed, 7 Dec 2016 10:24:38 -0500 Received: from mail-wj0-f170.google.com ([209.85.210.170]:33879 "EHLO mail-wj0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753211AbcLGPYg (ORCPT ); Wed, 7 Dec 2016 10:24:36 -0500 Date: Wed, 7 Dec 2016 15:24:34 +0000 From: Matt Fleming To: David Howells Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: Does anything ever enter through startup_64 in head_64.S? Message-ID: <20161207152434.GB5462@codeblueprint.co.uk> References: <21775.1481123477@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <21775.1481123477@warthog.procyon.org.uk> User-Agent: Mutt/1.5.24+41 (02bc14ed1569) (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 07 Dec, at 03:11:17PM, David Howells wrote: > Hi Matt, > > Does anything ever enter the kernel through startup_64 in head_64.S?[*] Do > all 64-bit mode entries always enter through one of the EFI entry points? Which head_64.S? There are two ;-) Assuming you mean startup_64 in boot/compressed/head_64.S, then the answer is "yes". 64-bit BIOS boot loaders will jump there. I'm fairly sure it's possible to boot that way on EFI too, you just lose some of the newer functionality that is dependent on the EFI boot stub. But I don't remember the last time I tried it. In general, we've always tried to maintain backwards compat, but you don't get the new features without switching to the EFI entry points. Whether or not any distros are still using the old 0x200 entry point for EFI is a good question, though.