go-delve/delve · error

invalid typecast for Dwarf instructions

Error message

invalid typecast for Dwarf instructions

What it means

In Reader.InstructionsForEntryNamed, the located entry's location attribute (AttrLocation or AttrDataMemberLoc depending on tag) must be a []byte DWARF expression. Any other value type yields this error, meaning the entry cannot provide executable location instructions.

Source

Thrown at pkg/dwarf/reader/reader.go:190

		return entry, nil
	}
	return nil, fmt.Errorf("could not find symbol value for %s", name)
}

func (reader *Reader) InstructionsForEntryNamed(name string, member bool) ([]byte, error) {
	entry, err := reader.FindEntryNamed(name, member)
	if err != nil {
		return nil, err
	}
	var attr dwarf.Attr
	if member {
		attr = dwarf.AttrDataMemberLoc
	} else {
		attr = dwarf.AttrLocation
	}
	instr, ok := entry.Val(attr).([]byte)
	if !ok {
		return nil, errors.New("invalid typecast for Dwarf instructions")
	}
	return instr, nil
}

func (reader *Reader) InstructionsForEntry(entry *dwarf.Entry) ([]byte, error) {
	if entry.Tag == dwarf.TagMember {
		instructions, ok := entry.Val(dwarf.AttrDataMemberLoc).([]byte)
		if !ok {
			return nil, errors.New("member data has no data member location attribute")
		}
		// clone slice to prevent stomping on the dwarf data
		return append([]byte{}, instructions...), nil
	}

	// non-member
	instructions, ok := entry.Val(dwarf.AttrLocation).([]byte)
	if !ok {
		return nil, errors.New("entry has no location attribute")

View on GitHub (pinned to a23773e6c3)

Solutions

1. Use InstructionsForEntry on an entry known to carry a static expression
2. Fall back to full variable evaluation through proc when the attribute is a location list
3. Dump the entry's attributes to confirm the form before extracting instructions

func hasByteLocation(e *dwarf.Entry) bool {
    attr := dwarf.AttrLocation
    if e.Tag == dwarf.TagMember { attr = dwarf.AttrDataMemberLoc }
    _, ok := e.Val(attr).([]byte)
    return ok
}

When it happens

Trigger: InstructionsForEntryNamed on an entry whose AttrLocation/AttrDataMemberLoc is nil or a non-[]byte form (e.g., location list, constant), or on an entry lacking the attribute altogether.

Common situations: Querying variables that are in registers via loclists, constant-valued enum members with AttrConstValue instead of member location, or optimized builds where Go emits location lists.

Related errors

• type assertion failed
• ErrStackUnderflow
• ErrStackIndexOutOfBounds
• ErrMemoryReadUnavailable
• empty OP stack

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/afbf6df8acc1dd45. Report an issue: GitHub.