{"record":{"id":"be3fa0b709768a7d","repo":"go-delve/delve","slug":"could-not-load-swiss-table-groups-lengthmask-field","errorCode":null,"errorMessage":"could not load swiss table groups lengthMask field: %v","messagePattern":"could not load swiss table groups lengthMask field: (.+?)","errorType":"exception","errorClass":null,"httpStatus":null,"severity":"error","filePath":"pkg/proc/mapiter.go","lineNumber":635,"sourceCode":"\tif err != nil {\n\t\tit.v.Unreadable = fmt.Errorf(\"could not load swiss table index: %v\", err)\n\t\treturn\n\t}\n\n\tgroups, err2 := tab.toField(it.tableFieldGroups)\n\tif err2 != nil {\n\t\tit.v.Unreadable = fmt.Errorf(\"could not load swiss table groups field: %v\", err2)\n\t\treturn\n\t}\n\tr.groups, err2 = groups.toField(it.groupsFieldData)\n\tif err2 != nil {\n\t\tit.v.Unreadable = fmt.Errorf(\"could not load swiss table groups data: %v\", err2)\n\t\treturn\n\t}\n\n\tfield, err2 = groups.toField(it.groupsFieldLengthMask)\n\tif err2 != nil {\n\t\tit.v.Unreadable = fmt.Errorf(\"could not load swiss table groups lengthMask field: %v\", err2)\n\t\treturn\n\t}\n\tgroupsLengthMask, err := field.asUint()\n\tif err != nil {\n\t\tit.v.Unreadable = fmt.Errorf(\"could not load swiss table group lengthMask: %v\", err)\n\t\treturn\n\t}\n\n\t// convert the type of groups from *group to *[len]group so that it's easier to use\n\tr.groups.DwarfType = pointerTo(fakeArrayType(groupsLengthMask+1, it.groupType), it.v.bi.Arch)\n\tr.groups.RealType = r.groups.DwarfType\n\tr.groups = r.groups.maybeDereference()\n\n\tif r.groups.Addr == 0 {\n\t\tit.v.Unreadable = errSwissTableNilGroups\n\t\treturn\n\t}\n","sourceCodeStart":617,"sourceCodeEnd":653,"githubUrl":"https://github.com/go-delve/delve/blob/a23773e6c31361e43246bc43a424ee009679b174/pkg/proc/mapiter.go#L617-L653","documentation":"Set on a map Variable while Delve reads the 'lengthMask' field (group count mask) of the swiss map groups struct. groups.toField(it.groupsFieldLengthMask) failed to resolve or read the field. Delve throws it because it needs lengthMask to compute the number of groups ([lengthMask+1]group) for the fake array type used during iteration.","triggerScenarios":"Iterating a swiss map when the maps.groups struct in the debuggee has no 'lengthMask' field resolvable via DWARF, or reading that field's memory fails.","commonSituations":"Go version where the groups struct field is named or laid out differently; DWARF truncated by build flags; attaching to a process built by a newer Go than Delve supports.","solutions":["Upgrade Delve so its expected groups struct fields match your Go runtime","Rebuild without debug-info stripping flags (-w, -s)","Confirm the target binary's Go version with 'go version <binary>'","Inspect the map through alternate means (fmt.Println in the program, len())"],"exampleFix":null,"handlingStrategy":"type-guard","validationCode":"if v.Unreadable != nil { return v.Unreadable } // swiss map fields unresolvable; upgrade Delve/rebuild target","typeGuard":"func inspectable(v *proc.Variable) bool { return v != nil && v.Unreadable == nil && v.Kind == reflect.Map }","tryCatchPattern":"if v.Unreadable != nil { fallbackToLenOnlyView(v); return }","preventionTips":["Pin Go versions to those listed as supported by your Delve build","Never strip DWARF from binaries you intend to debug","Test map inspection on a trivial program after toolchain upgrades","Treat Unreadable as a first-class error in all variable-handling code paths"],"tags":["go","debugger","dwarf","swiss-map"],"backgroundTag":"swiss-map-layout-mismatch","analyzedSha":"a23773e6c31361e43246bc43a424ee009679b174","analyzedAt":"2026-08-31T15:12:45.221Z","schemaVersion":2},"datasetVersion":"2026-08-31T19:17:28.585Z"}