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Alan Maguire says: ==================== bpf: Extend BTF UAPI vlen, kinds to use unused bits Currently BTF types can have a maximum of 65535 vlen-specified objects. While this limit has not yet been surpassed for existing cases (struct/union fields, enum values, function arguments and datasec), upcoming BTF location information - specifically inline sites - will hit that limit. Utilize unused BTF info bits in struct btf_type to increase limit to 24-bits (over 16 million). This is more than an order of magnitude greater than inline site counts for the kernel (~400,000) so should be enough for the near future at least. Similarly, struct btf_type uses 5 bits for BTF kind values; currently we use 20 kinds, but BTF location information will take another 3, and conceivably providing better support for Rust types in BTF (now that modules can be built using Rust) could push us close to the max of 31. Use 2 unused bits to provide a max possible kind of 127. Patch 1 handles UAPI and kernel-related changes. Patch 2 updates libbpf to have btf_vlen() return a __u32 instead of __u16 and updates consumers in libbpf accordingly. Also adds bounds checking for max vlen. Patch 3 cleans up __u16 vlen usage in bpftool. Patch 4 fixes up a test that relies on BTF info overflowing maximum kind value; fix up the expected error to be an invalid kind rather than (now impossible) invalid btf_info. Patch 5 fixes up __u16 vlen usage in selftests/bpf. Patch 6 syncs BTF documentation with UAPI changes. Changes since v2 [1]: - dropped backwards-compatibility macros (Alexei, patch 1) - added additional vlen bounds check in btf__add_field() (sashiko, bpf bot, patch 2) - dropped sanitization check in libbpf as older kernels will reject BTF with extended vlen/kinds using BTF info mask (Alexei) - fix more vlen assumptions in prog_test/ctx_rewrite.c (sashiko, patch 5) Changes since v1 [2]: - added redundant macros to UAPI in case enum switch for BTF_MAX* values causes problems (sashiko, patch 1) - updated feature test to use BTF loading rather than vmlinux BTF lookup, in line with other BTF feature tests (sashiko, patch 3) - fixed up a few more kernel, libbpf, bpftool instances of __u16 usage (bpf bot, sashiko, patches 1, 2, 4) - fixed up sanitize selftest cleanup (Mykyta, patch 5) - used unlikely-to-be-used kind (sashiko, patch 6) - fixed a few lingering selftests uses of __u16 for kind (patch 7) - update btf.rst with new vlen, kind sizes (patch 8) [1] https://lore.kernel.org/bpf/20260416143904.1220662-1-alan.maguire@oracle.com/ [2] https://lore.kernel.org/bpf/20260414195019.684531-1-alan.maguire@oracle.com/ ==================== Link: https://patch.msgid.link/20260417143023.1551481-1-alan.maguire@oracle.com Signed-off-by: Alexei Starovoitov <ast@kernel.org> |
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Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. Quick Start ----------- * Report a bug: See Documentation/admin-guide/reporting-issues.rst * Get the latest kernel: https://kernel.org * Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst * Join the community: https://lore.kernel.org/ Essential Documentation ----------------------- All users should be familiar with: * Building requirements: Documentation/process/changes.rst * Code of Conduct: Documentation/process/code-of-conduct.rst * License: See COPYING Documentation can be built with make htmldocs or viewed online at: https://www.kernel.org/doc/html/latest/ Who Are You? ============ Find your role below: * New Kernel Developer - Getting started with kernel development * Academic Researcher - Studying kernel internals and architecture * Security Expert - Hardening and vulnerability analysis * Backport/Maintenance Engineer - Maintaining stable kernels * System Administrator - Configuring and troubleshooting * Maintainer - Leading subsystems and reviewing patches * Hardware Vendor - Writing drivers for new hardware * Distribution Maintainer - Packaging kernels for distros * AI Coding Assistant - LLMs and AI-powered development tools For Specific Users ================== New Kernel Developer -------------------- Welcome! Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. Communication and Support ========================= * Mailing Lists: https://lore.kernel.org/ * IRC: #kernelnewbies on irc.oftc.net * Bugzilla: https://bugzilla.kernel.org/ * MAINTAINERS file: Lists subsystem maintainers and mailing lists * Email Clients: Documentation/process/email-clients.rst