go-delve/delve · error · errMapBucketContentsInconsistentLen

malformed map type: inconsistent array length in bucket

Error message

malformed map type: inconsistent array length in bucket

What it means

errMapBucketContentsInconsistentLen is returned when the keys, values, or tophash arrays inside a map bucket have inconsistent lengths: the Go runtime guarantees they all have bucketCnt (8) entries, so a mismatch means the parsed type layout is invalid. Delve rejects the map rather than producing wrong results.

Source

Thrown at pkg/proc/mapiter.go:127

	keyTypeIsPtr, elemTypeIsPtr bool

	tophashes *Variable
	keys      *Variable
	values    *Variable
	overflow  *Variable

	maxNumBuckets uint64 // maximum number of buckets to scan

	idx int64

	hashTophashEmptyOne uint64 // Go 1.12 and later has two sentinel tophash values for an empty cell, this is the second one (the first one hashTophashEmptyZero, the same as Go 1.11 and earlier)
	hashMinTopHash      uint64 // minimum value of tophash for a cell that isn't either evacuated or empty
}

var (
	errMapBucketContentsNotArray        = errors.New("malformed map type: keys, values or tophash of a bucket is not an array")
	errMapBucketContentsInconsistentLen = errors.New("malformed map type: inconsistent array length in bucket")
	errMapBucketsNotStruct              = errors.New("malformed map type: buckets, oldbuckets or overflow field not a struct")
)

func (it *mapIteratorClassic) nextBucket() bool {
	if it.overflow != nil && it.overflow.Addr > 0 {
		it.b = it.overflow
	} else {
		it.b = nil

		if it.maxNumBuckets > 0 && it.bidx >= it.maxNumBuckets {
			return false
		}

		for it.bidx < it.numbuckets {
			it.b = it.buckets.clone()
			it.b.Addr += uint64(it.buckets.DwarfType.Size()) * it.bidx

			if it.oldbuckets.Addr <= 0 {

View on GitHub (pinned to a23773e6c3)

Solutions

1. Update delve to match the Go version used to build the target (check delve release notes for Go support)
2. Rebuild and reattach so debug info matches the running code
3. Verify the map wasn't corrupted in the debuggee (panic/corruption elsewhere)
4. Pin a delve release known to work with your Go toolchain

// bucket arrays must all have bucketCnt (8) elements
if len(bkt.Field("keys").Type.(*godwarf.ArrayType).Count) != bucketCnt { /* reject */ }

m, err := loadMap(v)
if err != nil {
    if errors.Is(err, proc.ErrMapBucketContentsInconsistentLen) || strings.Contains(err.Error(), "inconsistent array length") {
        return fmt.Errorf("map layout invalid for this delve version: %w", err)
    }
    return err
}

When it happens

Trigger: loadMap/map iteration on a map whose bucket DWARF types declare arrays of differing lengths, typically due to Go version/Delve version mismatch or malformed debug info.

Common situations: Debugging a binary built with a Go release whose bucket layout differs from what delve expects; corrupted memory reads; stripped or third-party toolchains emitting nonstandard DWARF.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• malformed map type: keys, values or tophash of a bucket is n
• wrong real type for map
• malformed map type: buckets, oldbuckets or overflow field no
• malformed map type
• swiss table type does not have some required fields

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/1b8a6aeb8e94d60a. Report an issue: GitHub.