go-delve/delve · error

could not load swiss table groups data: %v

Error message

could not load swiss table groups data: %v

What it means

Set on a map Variable while Delve drills into the groups field of a swiss map table: after fetching the 'groups' struct field it dereferences it to the inner maps.groups (old/new) struct and reads its 'data' field. Failure means the nested field could not be resolved from DWARF or read from target memory. Delve throws it because the actual group array pointer cannot be located without this field.

Source

Thrown at pkg/proc/mapiter.go:629

	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
	}

	field, err2 = groups.toField(it.groupsFieldLengthMask)
	if err2 != nil {
		it.v.Unreadable = fmt.Errorf("could not load swiss table groups lengthMask field: %v", err2)
		return
	}
	groupsLengthMask, err := field.asUint()
	if err != nil {
		it.v.Unreadable = fmt.Errorf("could not load swiss table group lengthMask: %v", err)
		return
	}

	// convert the type of groups from *group to *[len]group so that it's easier to use
	r.groups.DwarfType = pointerTo(fakeArrayType(groupsLengthMask+1, it.groupType), it.v.bi.Arch)
	r.groups.RealType = r.groups.DwarfType
	r.groups = r.groups.maybeDereference()

View on GitHub (pinned to a23773e6c3)

Solutions

1. Upgrade Delve to the latest release supporting your Go version
2. Rebuild the binary with the supported Go toolchain and full DWARF
3. Re-inspect the map while the process is stopped at a stable breakpoint (avoid stale reads after mutation)
4. If debugging a core dump, ensure the dump was taken with a compatible Go/Delve pair

if v == nil || v.Unreadable != nil { return } // stale or unreadable map variable; re-evaluate at breakpoint

func fresh(v *proc.Variable) bool { return v != nil && v.Unreadable == nil }

if err := v.Unreadable; err != nil { reevaluateAtBreakpoint(); return }

When it happens

Trigger: Iterating a swiss map whose maps.groups struct lacks a readable 'data' field in debug info, or whose groups pointer points to unreadable memory (e.g. freed/corrupted table).

Common situations: Go runtime internals changed between versions (groups union layout); inspecting stale heap memory of a live mutating map during aggressive GC; binaries built with mismatched toolchain/Delve combination.

Related errors

• could not load swiss table index: %v
• could not load swiss table groups field: %v
• could not load swiss table groups lengthMask field: %v
• could not load swiss table group lengthMask: %v
• could not load swiss map group: %v

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/1ee77e62385be8a0. Report an issue: GitHub.