cilium/cilium · error

unsupported encoding %v

Error message

unsupported encoding %v

What it means

For btf.Integer, varGoValue only recognizes Signed, Unsigned and Bool encodings. Any other Encoding value (e.g. character or bitfield-flavored encodings from certain toolchains) has no mapping, so the generator refuses to emit a default.

Source

Thrown at tools/dpgen/config.go:257

				return nil, fmt.Errorf("unsupported signed integer size %d", t.Size)
			}
		case btf.Unsigned:
			switch t.Size {
			case 1:
				return getValue[uint8](v)
			case 2:
				return getValue[uint16](v)
			case 4:
				return getValue[uint32](v)
			case 8:
				return getValue[uint64](v)
			default:
				return nil, fmt.Errorf("unsupported unsigned integer size %d", t.Size)
			}
		case btf.Bool:
			return getValue[bool](v)
		default:
			return nil, fmt.Errorf("unsupported encoding %v", t.Encoding)
		}

	case *btf.Union:
		needUtils = true
		return getCastValue(t.Name, t.Size, v, typesPkg)

	case *btf.Struct:
		needUtils = true
		return getCastValue(t.Name, t.Size, v, typesPkg)

	default:
		return "", fmt.Errorf("unsupported type %T", t)
	}
}

func getValue[T comparable](v *ebpf.VariableSpec) (out T, err error) {
	if err := v.Get(&out); err != nil {
		return out, fmt.Errorf("getting value: %w", err)

View on GitHub (pinned to ac7b90affa)

Solutions

1. Replace the type with an explicitly signed/unsigned type or bool so the encoding is one of the three supported.
2. Rebuild with a supported clang/LLVM version with -g.
3. Inspect the actual Encoding via bpftool btf dump.
4. Extend the encoding switch in varGoValue if needed.

Example fix

// before (ambiguous encoding)
char mode;
// after
signed char mode; // or unsigned char / bool

if t, ok := btf.UnderlyingType(v.Type).(*btf.Int); ok {
    switch t.Encoding {
    case btf.Signed, btf.Unsigned, btf.Bool:
    default:
        return fmt.Errorf("%s: encoding %v unsupported", v.Name, t.Encoding)
    }
}

func hasSupportedIntEncoding(t btf.Type) bool {
    i, ok := btf.UnderlyingType(t).(*btf.Int)
    if !ok {
        return false
    }
    return i.Encoding == btf.Signed || i.Encoding == btf.Unsigned || i.Encoding == btf.Bool
}

When it happens

Trigger: A config variable whose BTF integer type reports an Encoding other than Signed/Unsigned/Bool while varGoValue runs.

Common situations: Plain 'char' whose encoding resolves oddly across clang versions, or objects built by a compiler emitting encodings the generator doesn't anticipate.

Related errors

• generating config struct: %w
• variable %s has no type information, was the ELF built witho
• variable %s has no doc comment
• variable %s: converting tags to comments: %w
• variable %s: getting default Go value: %w

AI-assisted analysis of cilium/cilium@ac7b90affa (2026-08-31). Data as JSON: /api/errors/b91019af9d4028bd. Report an issue: GitHub.