go-delve/delve · error · errSwissMapBadType

swiss table type does not have some required fields

Error message

swiss table type does not have some required fields

What it means

Delve determines the swiss map's table and group types by inspecting the type of it.dirPtr (loadTypes). errSwissMapBadType is returned when the map's DWARF type lacks some required fields Delve needs to decode a swiss map, meaning the runtime type shape does not match what this Delve version understands.

Source

Thrown at pkg/proc/mapiter.go:382

type swissTable struct {
	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

View on GitHub (pinned to a23773e6c3)

Solutions

1. Update Delve to the latest version (it tracks Go runtime layout changes closely)
2. Match the debugging environment: check 'go version <binary>' and install the Delve built for that Go release
3. If using a GOEXPERIMENT build, verify Delve supports that experiment (e.g. GOEXPERIMENT=mapsplitgroup) or rebuild without it

Example fix

// before
$ dlv version
Delve Debugger 1.21.0   # predates swiss maps
// after
$ go install github.com/go-delve/delve/cmd/dlv@latest
$ dlv version
Delve Debugger 1.24.x

// Precheck toolchain compatibility before debugging maps:
//   $ go version ./mybinary   -> e.g. go1.24.1
//   $ dlv version             -> must support that release's swiss map layout

if strings.Contains(err.Error(), "swiss table type does not have") {
    return fmt.Errorf("Delve too old for Go %s swiss maps: %w; upgrade delve", goVer, err)
}

When it happens

Trigger: Evaluating a map in a Go 1.24+ binary whose hmap/swiss type, as parsed from DWARF, is missing fields Delve requires (e.g. dirPtr/dirLen or table fields absent) — immediately on the first map iteration step.

Common situations: Target built with a Go release whose swiss map struct layout changed while the installed Delve is older (or vice versa); unusual GOEXPERIMENT builds altering struct fields; binaries with incomplete DWARF for runtime types.

Related errors

• swiss table bad table field
• bad swiss map type, group type lacks some required fields
• 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/e87dd1a742bc488e. Report an issue: GitHub.