{"id":118783,"date":"2024-08-01T15:43:01","date_gmt":"2024-08-01T13:43:01","guid":{"rendered":"https:\/\/prohoster.info\/blog\/novosti-interneta\/plan-prekrashheniya-podderzhki-staryh-proczessorov-arm-v-yadre-linux"},"modified":"2024-08-01T15:43:01","modified_gmt":"2024-08-01T13:43:01","slug":"plan-prekrashheniya-podderzhki-staryh-proczessorov-arm-v-yadre-linux","status":"publish","type":"post","link":"https:\/\/prohoster.info\/en\/blog\/news\/plan-prekrashheniya-podderzhki-staryh-proczessorov-arm-v-yadre-linux","title":{"rendered":"Plan to End Support for Old ARM Processors in the Linux Kernel","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"
Arnd Bergmann, responsible for kernel packages at SUSE, announced in the Linux kernel developers mailing list a plan to remove code for supporting old ARM CPUs and their associated ABIs, instruction sets, and kernel features from the kernel and GCC build tools. The plan is currently at the RFC stage, meaning it is open for community discussion. If approved, the removal of old ARM processors is proposed to begin in Linux kernel 6.12, which is expected to be released in December. The first candidates for removal include ARMv4 (without removing ARMv4T), iWMMXt, BE32, and OABI. <\/p>\n
The discontinuation of support for old ARM CPUs in the kernel coincides with the discontinuation of support in GCC\u2014some of the CPUs scheduled for removal are already not supported in recent GCC branches, and some are planned for removal in future releases, which will simplify upgrading and implementing new features in the compiler. The removal of architecture support in GCC will require its removal from the kernel if the minimum supported version of GCC in the kernel is raised (currently, at least GCC version 5.1 is required to build the kernel). <\/p>\n
Architectures, chips, and extensions proposed for removal from the kernel: <\/p>\n
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ARMv3\u2014support has already been discontinued in GCC 9.\n
ARMv4\u2014used for still-in-use processors StrongARM and FA526, with the newest of these chips released about 20 years ago. Support for ARMv4 was discontinued in Debian 5.0. It is proposed to first discontinue support for ARMv4 in GCC, and a few years later in the kernel.\n
ARMv4T\u2014there are 6 families of SoCs with ARM720T, ARM920T, and ARM922T cores that are more common than SoCs based on ARMv4. Support for ARMv4T was discontinued in Debian 9.0. The kernel plans to discontinue support for ARMv4T no earlier than the end of support for ARMv5.\n
ARMv5\u2014used on about 1\/3 of all platforms supported in the kernel, but most of these platforms are nearing the end of their life cycle. Debian continues to support ARMv5, but due to the lack of FPU and atomic operations, maintaining support is becoming increasingly difficult and, likely soon, the Debian port for ARMv5 will be classified as unofficial.\n
Initial generations of ARMv6\u2014used in SoCs like ARM1136r0p (NXP i.MX31) and OMAP24xx (Nokia N8xx), but their support requires hacks to work in SMP kernels.\n
ARMv6K\u2014is used in ARM1176 (Raspberry Pi 1, AST2500) and ARM1136r1. There are no obstacles in the kernel to discontinue support, but in distributions, there are challenges due to non-compliance with the standard armv7-a+vfpv3-d16.\n
ARMv7-M\u2014is used in microcontrollers based on Cortex-M3\/M4\/M7, which remain the last supported chips in the kernel without a memory management unit (MMU). Work on kernels for systems without MMU was discontinued in 2017, after switching to the development of RTOSs such as Zephyr for such chips. It is proposed to remove support for ARMv7-M in 2027, ten years after the cessation of development, despite continued support in GCC.\n
iWMMXt \u2014 support for CPU ARMv7 PJ4 (MMP2, Berlin) has already been discontinued in the core, after which no systems using this instruction set remain in circulation. Support for iWMMXt has been dropped in Clang and is proposed for removal from GCC.\n
BE32 (big endian ARMv5) \u2014 is used only in one SoC, Intel IXP4xx. Older versions of Debian supported only the little-endian mode, but unresolved issues remain in the drivers. It is proposed to remove BE32 support from GCC and the kernel, as no attempts have been made to fix the issues in the drivers over the years.\n
BE8 (big-endian ARMv7) \u2014 many drivers have issues, testing has ceased, and there is no information on devices still in use. The BE8 mode may be of interest for testing user-space components on big-endian systems, so support for BE8 is planned to be maintained in the kernel and GCC for at least a few more years until it begins to cause problems. <\/ul>\n
Proposed kernel Linux features for removal: <\/p>\n
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The param_struct structure, used until ATAGS (ARM Tag-Area) \u2014 was declared deprecated back in 2001, but is still used in code for RiscPC and Footbridge platforms.\n
Files with parameters based on the ATAGS structure (which were used to pass configuration information before the Device Tree) \u2014 there are 29 files related to 10 SoC platforms using ATAGS remaining in the kernel.\n
OABI (Old ABI, old ABI for the ARM architecture) \u2014 is almost universally replaced by EABI (Embedded ABI). OABI causes many errors, as driver developers have stopped taking into account certain related features. Support for OABI when building components for user space was discontinued in GCC 4.8, but the flag \u2018-mabi=apcs-gnu\u2019 remains for the kernel. It is proposed to keep OABI for now, but complicate its inclusion by oversight.\n
The OABI compatibility mode (OABI_COMPAT) \u2014 allows the execution of binaries built for OABI using a kernel with EABI. There are separate issues in drivers due to incompatibility with ioctl, but the maintenance effort for this mode is noticeably less than maintaining kernels with OABI. To preserve support for StrongARM, it would be sensible to keep support for OABI or OABI_COMPAT.\n
NWFPE (No Floating Point Emulator, an emulator for floating point operations) \u2014 patches for removal were proposed 11 years ago, but NWFPE is required for the operation of some userspace components compiled for OABI, so it is recommended to maintain support for NWFPE as long as support for OABI or OABI_COMPAT remains in the kernel.\n
Highmem (used for managing memory in areas above 1GB) \u2014 most ARM systems can operate without enabling highmem or can use CONFIG_VMSPLIT_2GB to access the first 2GB of physical memory. Work is underway to enable access to 4GB of RAM on LPAE systems (Cortex-A7\/A15), after which support for Highmem may be removed.\n
Sparsemem \u2014 required for systems that need highmem. <\/ul>\n
Proposed for removal platforms: <\/p>\n
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RiscPC \u2014 the oldest of the supported platforms in the kernel. It is no longer supported in GCC starting with the 9.x branch due to the removal of support for ARMv3. The maintainer continues to test kernel operation on this platform, but there seem to be no real users left, so support may be discontinued if the maintainer loses interest.\n
SA1100, Footbridge \u2014 obsolete platforms retained for nostalgia. Almost all files describing boards for these platforms were removed in kernel 6.3, leaving only support for the ipaq h3600, assabet, netwinder, and ebsa285 devices. The decision to remove them depends on the intentions of the maintainer.\n
Gemini, Moxart \u2014 use CPUs based on ARMv4. The chips were released over 20 years ago, but their support does not require additional maintenance efforts, so there is no point in removing them until the StrongARM platform is removed.\n
Files for supporting PXA \u2014 the platform is in a neglected state and has fallen out of use; if interest does not return, they intend to remove it in early 2025.\n
OMAP1 \u2014 on one hand, it remains the only platform based on ARMv4T\/ARMv5 without Device Tree support and there has been no movement towards transitioning to Device Tree, but on the other hand, the platform still has users.\n
Nspire, AT91RM9200, CLPS711X, EP93xx, iMX1 \u2014 use CPUs based on ARMv4T. Work is underway to transition board descriptions to Device Tree, but there is still a reason to maintain support for them as long as ARMv5 support is retained.\n
OMAP24xx \u2014 the only platform based on ARMv6 with active users. Continued support depends on maintaining support for the arm1136r0 CPU.\n
iMX31 \u2014 there is no information regarding active users, but there is no reason to remove it before OMAP2.\n
S3C64xx (Cragganmore) \u2014 the only platform without Device Tree support, built on ARMv6K. The platform continues to be used for testing audio codecs, so its removal is delayed until testing is transitioned to another board.\n
Orion5x, mv78xx0 \u2014 the issue of removal is planned to be considered at the beginning of next year.\n
iMX35, WM8750, AST2500, BCM2835 \u2014 are well supported and have active users, so removal is not planned for now.\n
stm32f4\/f7\/h7 \u2014 microcontrollers without an MMU, support in the kernel continues, and there are active users. The question of removal is planned to be reviewed in 2026. <\/ul>\n