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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.0 Subject: Re: [PATCH 0/3] linux-custom: Split up binaries from kernel headers to kbuild packages Content-Language: en-US To: "Koch, Stefan (DI PA DCP R&D 3)" , "isar-users@googlegroups.com" Cc: "Sudler, Simon (DI PA DCP TI)" , "Storm, Christian (T CED SES-DE)" , "Adler, Michael (T CED SES-DE)" References: <20221109103238.1520091-1-stefan-koch@siemens.com> <14a5cc80a0fb2a73c1839a79852449b6e5f1434e.camel@siemens.com> From: Jan Kiszka In-Reply-To: <14a5cc80a0fb2a73c1839a79852449b6e5f1434e.camel@siemens.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: FR2P281CA0017.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:a::27) To AS4PR10MB6181.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:20b:588::19) Return-Path: jan.kiszka@siemens.com MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: AS4PR10MB6181:EE_|DB5PR10MB7750:EE_ X-MS-Office365-Filtering-Correlation-Id: a66bad22-ce62-44f8-d8d0-08dac34a1ed7 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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Solve already known isar custom kernel >>>>> limitations from doc/custom_kernel.inc >>>>> - kernel headers package does not support both native >>>>>   and cross compilation of kernel modules when cross built >>>> >>>> Right, that requires building packages for multiple >>>> architectures. >>> >>> Important feature... Maybe it should be added to the TODO list in >>> the >>> docs? >>> >>>> This >>>> is the feature we need, and it has nothing to do with the kernel >>>> packages per se. >>> >>> The way that I assume debian will do building the kernel is that >>> they >>> use a generic debian defconfig for each architecture. >>> E. g. linux-config-5.10/config.amd64_none_amd64.xz, linux-config- >>> 5.10/config.arm64_none_arm64.xz >>> >>> ISAR builds are often using specific defconfigs honored by ISAR's >>> linux-custom for the target build. >>> >>> Debian specific architecture builds (e. g. host and target, maybe >>> with >>> sbuild) for one target device, using target specific stripped-down >>> defconfigs, may not working properly. The kernel build for a >>> foreign >>> architecture (e. g. host) may fail because of an incompatible >>> defconfig. >>> >>> Debian provide a generic very similar defconfig for different >>> architectures, and they build the linux-image, linux-headers and >>> linux- >>> kbuild for each architecture: >>> - So I assume the linux-kbuild:amd64 was build with linux-config- >>> 5.10/config.amd64_none_amd64.xz >>> - So I assume the linux-kbuild:arm64 was build with linux-config- >>> 5.10/config.arm64_none_arm64.xz >>> >>> The debian generic defconfig may differ in some arch specific >>> points >>> but you can use the linux-kbuild:amd64 for a cross-build of linux- >>> image:arm64 because the resulting scripts and tools are from the >>> identical set. So mixing linux-headers with different archictecture >>> specific builds from linux-kbuild should work since the defconfigs >>> have >>> a "shared base" (e. g. both define CONFIG_HAVE_C_RECORDMCOUNT thats >>> needed for recordmcount utility as example). >> >> Sorry, I don't understand what role the config plays here. Isar is >> used >> to compile (usually) one specific kernel, Debian compiles a few >> generic >> ones. But the fact that Debian compile everything natively (for >> production) and we do cross-compilation is not related to different >> configs. >> > > I just wanted to point out for the future case when ISAR would support > a generic way to build packages for multiple architectures: This might > not be applicable to all kernel builds. E. g. because of the fact that > the used defconfig for a "specific kernel" is not compatible for a > multi architecture build, only for the architecture that the defconfig > was made for. > > Yes, it may work if you could specify different defconfigs for each > architecture. One goal of this patch was to provide the kbuild scripts > and tools just for host and target in a transparent way - without any > changes to the build process of existing ISAR users. Misunderstanding: I didn't meant to propose building the kernel-image package for multiple arch, only the then factored-out kbuild packages with the host tool (once for the build env, once for the target). > >> The answer to the problem "I need kernel headers on the target" right >> now is in Isar to build natively the kernel and, thus, the header >> package. Not optimal, but we still need this case too rarely to have >> cared about it more so far. >> >>> >>>> Jan >>>> >>>>> >>>>> 2. Honor recommendations for future from doc/custom_kernel.inc >>>>> - Generate kernel headers packages for both host and target >>>>>   when using cross build >>>>> >>>>> 3. Add extensions known from debian kernel packages structure >>>>> - Generate a kernel headers package without binaries >>>>> - Create specific kernel kbuild packages that >>>>>   will ship the "scripts" and "tools" binaries >>>>> - Use symlinks to point to the "scripts" and "tools" binaries >>>> >>>> Keep in mind that we intend to remain compatible with the layout >>>> of >>>> Debian. Self-built kernels should remain drop-in replacements of >>>> the >>>> Debian kernel packages. And that is true for development packages >>>> as >>>> well. >>>> >>>> So, are your changes working against that, or are they improving >>>> existing incompatibility with the debian packages? >>> >>> The approach from this patchset does build the kernel in the known >>> ISAR >>> specific way. Debian itself patches the kernel Makefiles to >>> modularize >>> the kernel build what ISAR doesn't do. With this patch the packages >>> linux-kbuild and linux-kbuild-cross are the only new packages that >>> the >>> ISAR build will provide. That means ISAR will provide then linux- >>> headers, linux-image and linux-kbuild. They match on the target >>> with >>> the package name of the respective debian packages. So the existing >>> drop-in should not be affected. >>> >>> In short this patch brings the ISAR linux-custom mechanism a bit >>> nearer >>> to the debian package structure. Since linux-headers behaves then >>> more >>> like the original debian linux-heades to ship the binaries within a >>> separate package -> linux-kbuild. >>> >>> The trick is to build only the scripts and tools with schroot- >>> target >>> (QEMU) in a non-cross way. Since the kernel does not support >>> building >>> the scripts and tools for target architecture when do a cross build >>> without patching the kernel Makefiles. I think that patch was never >>> merged into the kernel: >>> >>> https://patchwork.kernel.org/project/linux-kbuild/patch/1376046432-12588-1-git-send-email-broonie@kernel.org/ >>> >> >> The problem is that patch might have to not provide that use case I >> wrote about above. It is a rare use case, a non-distro use case, but >> I >> wouldn't call it an invalid one. If we can address it by splitting up >> the Isar kernel build into different packages and then only compile >> the >> binary bits once again, now for the target architecture, that would >> be a >> nice solution. > > That's what the patch do: > - Move the binary scripts and tools from linux-headers to linux-kbuild > as debian does it for their kernels > - Compile only the scripts and tools for the target using schroot- > target (QEMU) and package it as linux-kbuild > - Package the binary scripts and tools from the full cross kernel build > to linux-kbuild-cross using schroot-host It's moving in a good direction - but why linux-kbuild-cross? Nothing depends on it in your patches, thus module builds will be broken. I suspect we rather need KERNEL_PKG_KERN_KBUILD=linux-kbuild-${KERNEL_NAME_PROVIDED}: and therefore (on amd64) linux-kbuild-${KERNEL_NAME_PROVIDED}:amd64 to be built and then installed for module builds. Jan -- Siemens AG, Technology Competence Center Embedded Linux