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v0.21.0: Struct Ops, Weak Symbols and BTF deduplication

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@dylandreimerink dylandreimerink released this 05 Mar 15:30
· 5 commits to main since this release
v0.21.0
fd33a78

Hi, everyone! The Cilium project is proud to announce v0.21.0 of ebpf-go, our first major 2026 feature release. Please note that this version comes with a few breaking changes for XDP users that may require some intervention based on your use case, so please read the following section carefully before upgrading! We've also removed some long-deprecated APIs.

Breaking changes

XDP Attach Type

This release saw a change to the ELF parsing logic, specifically to XDP programs. Previously, XDP programs had their ProgramSpec.AttachType set to AttachNone. Prompted by upstream changes in Linux 6.18, XDP programs now come with an AttachXDP attach type. This change ensures compatibility with kernels going forward, as well as better interoperability with libbpf-based tools using shared PROG_ARRAY maps.

tl;dr: Linux 6.18 and later disallows mixing attach types within the same program array.

If your application uses a pinned program array, you may need to manually change the attach type of your XDP programs to AttachNone before they are loaded to ensure they can still be inserted into maps containing pre-upgrade programs.

The same goes for BPF links. If you're updating an XDP link created by an older version of ebpf-go, you need to ensure your XDP program is loaded with the same attach type the link was initially created with, or updating will fail with EINVAL.

For an example of how to deal with this change, here's the the Cilium PR that implemented logic to try both attach types when updating links.

Windows helper function rename

ebpf-for-windows was upgraded from 0.21.0 to v1.0.0-rc1. efW made breaking changes to the names of helper functions, our API has been updated to match:

New Features

  • Struct ops — The ELF reader can now parse struct ops sections, building MapSpecs and resolving function-pointer members. link.AttachStructOps has been added to allow attaching a StructOpsMap as a link. A sched_ext example can be found here.
  • Weak symbol & ELF linking — Programs and maps defined as weak symbols are now fully supported. The ELF reader performs per-symbol decoding for both ProgramSpec and MapSpec, meaning linked objects (produced via bpftool gen object) are now handled correctly.
  • BTF type deduplication — btf.Builder can now deduplicate types while generating a BTF blob. Deduplication can be enabled by passing BuilderOptions to NewBuilder with the Deduplication field set to true.
  • ProgramSpec.Compatible was added — ProgramSpec.Tag is now deprecated. The new ProgramSpec.Compatible method compares a loaded program's tag against both SHA-1 and SHA-256 hashes of the spec, ensuring correct behaviour across kernels — including kernel v6.18+, which switched to SHA-256 for program hashing.
  • ProgramInfo improvements — The program name as reported by ProgramInfo.Name is now sourced from BTF func info when available to provide the full program name if it's longer than 15 bytes.
  • LinkInfo improvements — Added a number of methods and types related to reading back link info.
  • Reverse symbol lookup — Added Executable.Symbol to resolve addresses to a symbol and relative offset.
  • Uprobe/kprobe link feature probing — HaveBPFLinkKprobeMulti, HaveBPFLinkUprobeMulti, and HaveBPFLinkKprobeSession are now exported from the features package, making it easier to probe for multi-attach support before loading programs.
  • Program run batching — A new RunOptions.BatchSize option has been added to support batching when running programs.

Bug Fixes

  • Allow weak kfuncs loading without CAP_SYS_ADMIN — Loading programs with weak kfuncs on kernels that don't have the kfunc no longer fails with "operation not permitted" when the caller lacks CAP_SYS_ADMIN. The permission error is now treated as "not found" for weak kfuncs.
  • ELF reader nil panic — Fixed a panic that could occur when loading an ELF without BTF due to a nil extInfo pointer. Along with the fix, a suite of regression tests was added that exercises the core loader logic with non-BTF ELFs as well.
  • QueryResult.HaveLinkInfo heuristic — The heuristic has been updated to check for at least one attached program with a non-zero link ID, fixing a false positive introduced by a kernel change that began populating the revision field for cgroup queries.
  • Windows map/program count — Increased the default map and program count on Windows to reduce failures when loading collections with more maps than previously allocated.

More breaking changes

Deprecations

In this release we have removed a number of features which had been deprecated for a while.

Breaking changes to Memory, Variable and VariableSpec

Breaking changes to link info

Breaking changes to BTF API

We exported methods and types from the btf package. This allowed us to directly assign BTF func info, line info and CO-RE relocations to instructions from outside of the btf package, making some methods unneeded and thus got removed.

What's Changed

New Contributors

Full Changelog: v0.20.0...v0.21.0

Contributors

chantra, lmb, and 13 other contributors
Assets 2
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