go-delve/delve · error · errSwissMapBadGroupTypeErr

bad swiss map type, group type lacks some required fields

Error message

bad swiss map type, group type lacks some required fields

What it means

The swiss map iterator needs the group struct to contain specific fields to read key/elem slots. errSwissMapBadGroupTypeErr is returned by loadTypes when the group type found in the target's DWARF lacks some required fields, so Delve cannot decode groups of the map.

Source

Thrown at pkg/proc/mapiter.go:384

	index  int64
	groups *Variable
}

type swissGroup struct {
	ctrls []byte

	// GOEXPERIMENT=nomapsplitgroup
	slots *Variable

	// GOEXPERIMENT=mapsplitgroup
	keys, elems *Variable
}

var (
	errSwissTableCouldNotLoad  = errors.New("could not load one of the tables")
	errSwissMapBadType         = errors.New("swiss table type does not have some required fields")
	errSwissMapBadTableField   = errors.New("swiss table bad table field")
	errSwissMapBadGroupTypeErr = errors.New("bad swiss map type, group type lacks some required fields")
	errSwissTableNilGroups     = errors.New("bad swiss map, groups pointer is nil")
)

// loadTypes determines the correct type for it.dirPtr:  the linker records
// this type as **table but in reality it is either *[dirLen]*table for
// large maps or *group for small maps, when it.dirLen == 0.
func (it *mapIteratorSwiss) loadTypes() {
	tableptrptrtyp, ok := it.dirPtr.DwarfType.(*godwarf.PtrType)
	if !ok {
		it.v.Unreadable = errSwissMapBadTableField
		return
	}
	tableptrtyp, ok := tableptrptrtyp.Type.(*godwarf.PtrType)
	if !ok {
		it.v.Unreadable = errSwissMapBadTableField
		return
	}
	it.tableType, ok = tableptrtyp.Type.(*godwarf.StructType)

View on GitHub (pinned to a23773e6c3)

Solutions

1. Update Delve to the version matching the target binary's Go release
2. Rebuild the binary with a standard Go release and full debug symbols
3. Confirm no GOEXPERIMENT is active that changes map internals, or use a Delve build that supports it

// Verify no layout-altering experiments and matching toolchain:
//   $ go env GOEXPERIMENT   # should be empty for debug builds
//   $ go version <binary> && dlv version

When it happens

Trigger: Evaluating a swiss map when the resolved group type (from the table's groups field or, for small maps, from dirPtr when dirLen==0) is missing required group fields during loadTypes.

Common situations: Go runtime releases that changed internal/runtime/maps.group layout while an older Delve is used; custom GOEXPERIMENT builds; binaries whose runtime type info was altered or partially stripped.

Related errors

• swiss table type does not have some required fields
• swiss table bad table field
• wrong real type for map
• malformed map type: keys, values or tophash of a bucket is n
• malformed map type: inconsistent array length in bucket

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/785445976e70f410. Report an issue: GitHub.