cilium/cilium · error

making Blocks for ProgramSpec %s: %w

Error message

making Blocks for ProgramSpec %s: %w

What it means

After loading the collection spec, fetchOrCompile precomputes analyzer Blocks for every ProgramSpec via analyze.MakeBlocks. A per-program failure is wrapped as 'making Blocks for ProgramSpec <name>'. This indicates the control-flow/verifier pre-analysis of that program's instructions failed, usually a malformed or unsupported instruction sequence.

Source

Thrown at pkg/datapath/loader/cache.go:241

			)
		}
		return nil, "", err
	}

	obj.path = path

	obj.spec, err = ebpf.LoadCollectionSpec(path)
	if err != nil {
		return nil, "", fmt.Errorf("load eBPF ELF %s: %w", path, err)
	}

	// Precompute the Blocks for each ProgramSpec in the CollectionSpec so
	// downstream callers don't need to compute them again. This is expensive to
	// run, so do it only once per compilation. Control flow isn't expected to
	// be changed after compilation.
	for name, prog := range obj.spec.Programs {
		if _, err := analyze.MakeBlocks(prog.Instructions); err != nil {
			return nil, "", fmt.Errorf("making Blocks for ProgramSpec %s: %w", name, err)
		}
		o.logger.Debug("Precomputed Blocks", logfields.Object, name)
	}

	return obj.spec.Copy(), hash, nil
}

View on GitHub (pinned to ac7b90affa)

Solutions

1. Recompile the object with the supported clang/LLVM version
2. Check the named ProgramSpec against upstream template sources; revert local BPF patches
3. Update the agent (and its analyzer) to a version matching the object format
4. File/inspect an upstream issue if the stock template triggers it

// Compile objects with the toolchain version the analyzer supports
if !supportedToolchain(clangVersion) {
    return fmt.Errorf("clang %s unsupported for Blocks analysis", clangVersion)
}

if err != nil && strings.Contains(err.Error(), "making Blocks for ProgramSpec") {
    var specErr error
    errors.As(err, &specErr)
    log.Errorf("analyzer rejected program (%v); recompiling with pinned clang", specErr)
    invalidateCompiledCache()
    return recompileAndReload(ctx)
}

When it happens

Trigger: analyze.MakeBlocks(prog.Instructions) returning an error for a given program name in the freshly loaded spec — e.g. unexpected jump targets or instruction encoding the analyzer cannot handle.

Common situations: Objects compiled with a newer/older clang producing instruction patterns the bundled analyzer doesn't understand; custom or patched BPF programs inserted into the template; version mismatch between loader and compiled object.

Related errors

• failed to open template header for writing: %w
• failed to write template header: %w
• failed to compile template program: %w
• Failed to compile %s: %w
• Unable to determine if BPF_FIB_LOOKUP_SRC is supported

AI-assisted analysis of cilium/cilium@ac7b90affa (2026-08-31). Data as JSON: /api/errors/ec510a55d8740e9d. Report an issue: GitHub.