Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753954AbdHXQ5e (ORCPT ); Thu, 24 Aug 2017 12:57:34 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:44662 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753609AbdHXQ5d (ORCPT ); Thu, 24 Aug 2017 12:57:33 -0400 Date: Thu, 24 Aug 2017 17:56:17 +0100 From: Mark Rutland To: AKASHI Takahiro Cc: catalin.marinas@arm.com, will.deacon@arm.com, bauerman@linux.vnet.ibm.com, dhowells@redhat.com, vgoyal@redhat.com, herbert@gondor.apana.org.au, davem@davemloft.net, akpm@linux-foundation.org, mpe@ellerman.id.au, dyoung@redhat.com, bhe@redhat.com, arnd@arndb.de, ard.biesheuvel@linaro.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 08/14] arm64: kexec_file: create purgatory Message-ID: <20170824165617.GC29665@leverpostej> References: <20170824081811.19299-1-takahiro.akashi@linaro.org> <20170824081811.19299-9-takahiro.akashi@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170824081811.19299-9-takahiro.akashi@linaro.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1488 Lines: 39 On Thu, Aug 24, 2017 at 05:18:05PM +0900, AKASHI Takahiro wrote: > This is a basic purgtory, or a kind of glue code between the two kernel, > for arm64. We will later add a feature of verifying a digest check against > loaded memory segments. > > arch_kexec_apply_relocations_add() is responsible for re-linking any > relative symbols in purgatory. Please note that the purgatory is not > an executable, but a non-linked archive of binaries so relative symbols > contained here must be resolved at kexec load time. > Despite that arm64_kernel_start and arm64_dtb_addr are only such global > variables now, arch_kexec_apply_relocations_add() can manage more various > types of relocations. Why does the purgatory code need to be so complex? Why is it not possible to write this as position-independent asm? > +/* > + * Apply purgatory relocations. > + * > + * ehdr: Pointer to elf headers > + * sechdrs: Pointer to section headers. > + * relsec: section index of SHT_RELA section. > + * > + * Note: > + * Currently R_AARCH64_ABS64, R_AARCH64_LD_PREL_LO19 and R_AARCH64_CALL26 > + * are the only types to be generated from purgatory code. Is this all that has been observed, or is this ensured somehow? The arch_kexec_apply_relocations_add() function below duplicates a lot of logic that already exists in the arm64 module loader's apply_relocate_add() function. Please reuse that code. Having a duplicate or alternative implementation is just asking for subtle bugs. Thanks, Mark.