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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_NEOMUTT 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 A30AAC43219 for ; Wed, 1 May 2019 19:55:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6FEC820651 for ; Wed, 1 May 2019 19:55:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726196AbfEATzD (ORCPT ); Wed, 1 May 2019 15:55:03 -0400 Received: from mout.kundenserver.de ([212.227.126.133]:58361 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726004AbfEATzD (ORCPT ); Wed, 1 May 2019 15:55:03 -0400 Received: from excalibur.cnev.de ([213.196.200.188]) by mrelayeu.kundenserver.de (mreue010 [212.227.15.167]) with ESMTPSA (Nemesis) id 1M9WeC-1hRPUo41DA-005VNG; Wed, 01 May 2019 21:54:47 +0200 Received: from karsten by excalibur.cnev.de with local (Exim 4.89) (envelope-from ) id 1hLvJT-0000Cx-TE; Wed, 01 May 2019 21:54:43 +0200 Date: Wed, 1 May 2019 21:54:43 +0200 From: Karsten Merker To: Anup Patel Cc: Mark Rutland , "aou@eecs.berkeley.edu" , Palmer Dabbelt , "linux-kernel@vger.kernel.org" , "zong@andestech.com" , Atish Patra , "linux-riscv@lists.infradead.org" Subject: Re: [PATCH] RISC-V: Add an Image header that boot loader can parse. Message-ID: <20190501195443.trgjv6tujctsw5sw@excalibur.cnev.de> References: <20190501170053.GG11740@lakrids.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-No-Archive: yes User-Agent: NeoMutt/20170113 (1.7.2) X-Provags-ID: V03:K1:Wcvbk2phACwbUNrWanmcgvaG/SC1Qa2xqLynbBepDlxoWVqQ4EY Fk4o8lLOXe7Qyzqn5JoguFhonrfnGSpZ6l4q4tzGLSz2KFSBdPUCB7d4kfAEGaxjahIHdyp SlDodHWHDtDmnplGuKoJUWruDbJ3tzt8IQsyW8iR+KzpZ189HwyNhx8HI/cH54jKHaMbKuB 4ZWxGgAMRvkXt7LlylWkw== X-UI-Out-Filterresults: notjunk:1;V03:K0:J9tQ4OSZ3ao=:dzfbPsQ3MnrH1ztAiTmZ2B M1AuxzxvjtbGbGSa2DXCW7u6jfchZljqRTBBUaXGbVwN/3sK8XniHlx9tEm2wjO9sZzTkz0Tt eXw+lWbpOwAq4zOTBcR3729m0n600y6dqOVU1ZFwOhYCeTzxpn0UyQFDcx/i6Ut2khFjWjypZ FF965xlxk9joK+TrlEdnXqc07g+q5foKln6KVyL25UeNAT+gimLJVSEfBOcIFT4dOElj/VBOT FK2wWfVEOmw7wpyzIBGggfGvUyCekiBrDBHk/GJ+kjAAuhTBiTlue8f1cPz5vkLhFR8D4meTO L62RN1uAGYF7zJ+Sv40erBWz5JR5Uxu+Y8s6VelzQyF18Zj1I3oHXdV/Ql2dQ4PTI7CVNXtha TrkBxAWOXNqyl1BkC5ykYSTERZqG9jyYj8sgjMwOjANAM0YiyMWuOQoeb4lA+DW/hvOvIHpSa Z9egQj2ChHNTy94b74uIZCXr/etDH1ogIAGzeNL4wArefPlxLrisidR7D8wMVmk4w0S0Mbnaf v/V2V91qzPbwC6906PQ4OI3KIsAgp9EipA7SCHqagHbWcBaa6PbonXT/Zm4/rkwC8wUOYRTJE B1EgzfkBL8E4oE9mPlFWmE8qcEDcZGYX0FNrTZQc+26kzcQfdrGJmoQr+OuClPW26mVZPE7kh zpVHt0InM8kNJ1B5iT1WoVwYjr0+4dQwob6z8HosF2X2J8O5p8ah8waYUowMGFXeOCKxtk86Z 5yQ1kbjcMubeKe88OZ31WtLgmCTs20fJGzLrqA== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 01, 2019 at 10:41:52PM +0530, Anup Patel wrote: > On Wed, May 1, 2019 at 10:30 PM Mark Rutland wrote: > > On Mon, Apr 29, 2019 at 10:42:40PM -0700, Atish Patra wrote: > > > On 4/29/19 4:40 PM, Palmer Dabbelt wrote: > > > > On Tue, 23 Apr 2019 16:25:06 PDT (-0700), atish.patra@wdc.com wrote: > > > > > Currently, last stage boot loaders such as U-Boot can accept only > > > > > uImage which is an unnecessary additional step in automating boot flows. > > > > > > > > > > Add a simple image header that boot loaders can parse and directly > > > > > load kernel flat Image. The existing booting methods will continue to > > > > > work as it is. > > > > > > > > > > Tested on both QEMU and HiFive Unleashed using OpenSBI + U-Boot + Linux. > > > > > > > > > > Signed-off-by: Atish Patra > > > > > --- > > > > > arch/riscv/include/asm/image.h | 32 ++++++++++++++++++++++++++++++++ > > > > > arch/riscv/kernel/head.S | 28 ++++++++++++++++++++++++++++ > > > > > 2 files changed, 60 insertions(+) > > > > > create mode 100644 arch/riscv/include/asm/image.h > > > > > > > > > > diff --git a/arch/riscv/include/asm/image.h b/arch/riscv/include/asm/image.h > > > > > new file mode 100644 > > > > > index 000000000000..76a7e0d4068a > > > > > --- /dev/null > > > > > +++ b/arch/riscv/include/asm/image.h > > > > > @@ -0,0 +1,32 @@ > > > > > +/* SPDX-License-Identifier: GPL-2.0 */ > > > > > + > > > > > +#ifndef __ASM_IMAGE_H > > > > > +#define __ASM_IMAGE_H > > > > > + > > > > > +#define RISCV_IMAGE_MAGIC "RISCV" > > > > > + > > > > > +#ifndef __ASSEMBLY__ > > > > > +/* > > > > > + * struct riscv_image_header - riscv kernel image header > > > > > + * > > > > > + * @code0: Executable code > > > > > + * @code1: Executable code > > > > > + * @text_offset: Image load offset > > > > > + * @image_size: Effective Image size > > > > > + * @reserved: reserved > > > > > + * @magic: Magic number > > > > > + * @reserved: reserved > > > > > + */ > > > > > + > > > > > +struct riscv_image_header { > > > > > + u32 code0; > > > > > + u32 code1; > > > > > + u64 text_offset; > > > > > + u64 image_size; > > > > > + u64 res1; > > > > > + u64 magic; > > > > > + u32 res2; > > > > > + u32 res3; > > > > > +}; > > > > > > > > I don't want to invent our own file format. Is there a reason we can't just > > > > use something standard? Off the top of my head I can think of ELF files and > > > > multiboot. > > > > > > Additional header is required to accommodate PE header format. Currently, > > > this is only used for booti command but it will be reused for EFI headers as > > > well. Linux kernel Image can pretend as an EFI application if PE/COFF header > > > is present. This removes the need of an explicit EFI boot loader and EFI > > > firmware can directly load Linux (obviously after EFI stub implementation > > > for RISC-V). > > > > Adding the EFI stub on arm64 required very careful consideration of our > > Image header and the EFI spec, along with the PE/COFF spec. > > > > For example, to be a compliant PE/COFF header, the first two bytes of > > your kernel image need to be "MZ" in ASCII. On arm64 we happened to find > > a valid instruction that we could rely upon that met this requirement... > > The "MZ" ASCII (i.e. 0x5a4d) is "li s4,-13" instruction in RISC-V so this > modifies "s4" register which is pretty harmless from Linux RISC-V booting > perspective. > > Of course, we should only add "MZ" ASCII in Linux RISC-V image header > when CONFIG_EFI is enabled (just like Linux ARM64). Probably I'm missing something obvious, but I cannot completely follow you here. My understanding is as follows: The kernel gets executed by jumping to the _start label, where it currently immediately starts with setting up everything (mask interrupts, disable FPU, etc). Now we insert a structure before the actual init code where the first 64 bits of the structure (the code0 and code1 fields) are filled with values that constitute a valid jump opcode to the actual init code behind the end of the new structure. If the first byte in a PE/COFF header has to be an ASCII "M", that is 01001101 in binary. RISC-V is little-endian and the last two bits of the lowest-value byte define the type of instruction. According to the chapter "Base Instruction-Length Encoding" in the RISC-V ISA spec everything except 11 as the lowest bits denotes a compressed instruction and if I have puzzeled together the the various instruction bits correctly, ASCII "MZ" would be excuted as a compressed load immediate to x9/s1, wouldn't it? If my previous thoughts are correct, this would also mean that having a PE/COFF-compatible header for EFI boot would make a kernel image inherently incompatible with performing a non-EFI boot of the same image on systems that don't implement the C extension. As the work-in-progress RISC-V Unix platform spec will probably mandate C, that probably won't be much of a practical problem, though. Regards, Karsten -- Ich widerspreche hiermit ausdrücklich der Nutzung sowie der Weitergabe meiner personenbezogenen Daten für Zwecke der Werbung sowie der Markt- oder Meinungsforschung.