go-delve/delve · warning

could not load swiss table index field: %v

Error message

could not load swiss table index field: %v

What it means

When loading a table of a swiss map, the iterator dereferences the table pointer and extracts its index field. If reading that field from memory fails, the Variable is marked Unreadable with this error before iteration can continue.

Source

Thrown at pkg/proc/mapiter.go:613

	it.groupIdx++
	it.group = nil
}

// loadCurrentTable loads the table at index it.dirIdx into it.tab
func (it *mapIteratorSwiss) loadCurrentTable() {
	tab, err := it.dirPtr.sliceAccess(int(it.dirIdx))
	if err != nil || tab == nil || tab.Unreadable != nil {
		it.v.Unreadable = errSwissTableCouldNotLoad
		return
	}

	tab = tab.maybeDereference()

	r := &swissTable{}

	field, err2 := tab.toField(it.tableFieldIndex)
	if err2 != nil {
		it.v.Unreadable = fmt.Errorf("could not load swiss table index field: %v", err2)
		return
	}
	r.index, err = field.asInt()
	if err != nil {
		it.v.Unreadable = fmt.Errorf("could not load swiss table index: %v", err)
		return
	}

	groups, err2 := tab.toField(it.tableFieldGroups)
	if err2 != nil {
		it.v.Unreadable = fmt.Errorf("could not load swiss table groups field: %v", err2)
		return
	}
	r.groups, err2 = groups.toField(it.groupsFieldData)
	if err2 != nil {
		it.v.Unreadable = fmt.Errorf("could not load swiss table groups data: %v", err2)
		return
	}

View on GitHub (pinned to a23773e6c3)

Solutions

1. Use a delve build matching the target Go runtime version
2. Re-evaluate the map variable at the current stop point
3. Validate memory/core completeness; check for heap corruption in the target

Example fix

// before
dlv attach <pid> # dlv built for older Go, target uses swiss maps
// after
go install github.com/go-delve/delve/cmd/dlv@latest && dlv attach <pid>

if v.Unreadable != nil {
    return fmt.Errorf("map not readable: %v", v.Unreadable)
}

func isReadable(v *proc.Variable) bool {
    return v.Unreadable == nil
}

if err := loadCurrentTable(it); err != nil || it.v.Unreadable != nil {
    if it.v.Unreadable != nil && strings.Contains(it.v.Unreadable.Error(), "could not load swiss table") {
        return reEvaluateAndIterate(mapExpr)
    }
    return it.v.Unreadable
}

When it happens

Trigger: Evaluating a swiss map whose directory table pointer or index field lives in unreadable memory — corrupted directory entries, stale iterators after resize, or missing pages in core dumps.

Common situations: Debugging Go 1.24+ swiss maps with mismatched delve versions; inspecting maps from incomplete core files; examining heap-corrupted programs.

Related errors

• error accessing swiss map in table %d, group %d, slot %d
• error accessing swiss map slot: %v %v
• wrong real type for map
• unreadable tophash: %v
• malformed map type: keys, values or tophash of a bucket is n

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/c39c9225b498aeba. Report an issue: GitHub.