go-delve/delve · error

could not load swiss map group: %v

Error message

could not load swiss map group: %v

What it means

Set on a map Variable by loadCurrentGroup when sliceAccess on the groups array at it.groupIdx fails. Delve previously rewrote the groups pointer into a fake *[N]group array type; indexing it requires reading the group pointer at that array slot from target memory. Failure typically means the address is out of bounds of readable memory or the fake array index is invalid. Delve throws it because the group at the current index cannot be loaded.

Source

Thrown at pkg/proc/mapiter.go:661

	// 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()

	if r.groups.Addr == 0 {
		it.v.Unreadable = errSwissTableNilGroups
		return
	}

	it.tab = r
}

// loadCurrentGroup loads the group at index it.groupIdx of it.tab into it.group
func (it *mapIteratorSwiss) loadCurrentGroup() {
	group, err := it.tab.groups.sliceAccess(int(it.groupIdx))
	if err != nil {
		it.v.Unreadable = fmt.Errorf("could not load swiss map group: %v", err)
		return
	}

	g := &swissGroup{}

	var err2 error
	ctrl, err2 := group.toField(it.groupFieldCtrl)
	if err2 != nil {
		it.v.Unreadable = fmt.Errorf("could not load swiss map group ctrl: %v", err2)
		return
	}
	g.ctrls = make([]byte, ctrl.DwarfType.Size())
	_, err = ctrl.mem.ReadMemory(g.ctrls, ctrl.Addr)
	if err != nil {
		it.v.Unreadable = err
		return
	}

View on GitHub (pinned to a23773e6c3)

Solutions

1. Re-evaluate the map variable at a fresh breakpoint instead of using a stale copy captured before the map mutated
2. Upgrade Delve to match the Go runtime layout so group counts are computed correctly
3. Verify the process/core dump memory is fully available (full-heap core dump)
4. Reduce map inspection to len() and targeted key lookups if iteration keeps failing

if v.Unreadable != nil { return } // group memory unreadable; re-evaluate at a stable stop point

func usable(v *proc.Variable) bool { return v != nil && v.Unreadable == nil && v.Addr != 0 }

if v.Unreadable != nil { return nil, fmt.Errorf("map iteration stopped early: %w", v.Unreadable) }

When it happens

Trigger: Iterating a swiss map when the group pointer for groupIdx cannot be read: groups pointer corrupted, groupIdx exceeding the real allocation, or unreadable heap memory (detached/exited process, bad core dump).

Common situations: Inspecting a map whose memory was freed or reallocated (reading stale variables after program resumed); corrupt core dump; Delve miscalculating group count due to layout mismatch causing out-of-range reads.

Related errors

• could not load swiss table groups data: %v
• write out of bounds
• can not access unreadable map: %v
• could not load swiss table index: %v
• could not load swiss table groups field: %v

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/b62607204e9cc1f8. Report an issue: GitHub.