go-delve/delve · error

unsupported location expression for argument %s: %v

Error message

unsupported location expression for argument %s: %v

What it means

After successfully fetching the location program, Delve executes the DWARF stack program to compute the argument's CFA-relative offset. If ExecuteStackProgram itself errors (e.g. uses opcodes the evaluator doesn't implement), this error wraps the evaluation failure.

Source

Thrown at pkg/proc/fncall.go:694

	sort.Slice(formalArgs, func(i, j int) bool {
		return formalArgs[i].off < formalArgs[j].off
	})

	return argFrameSize, formalArgs, nil
}

func funcCallArgOldABI(fn *Function, bi *BinaryInfo, entry reader.Variable, argname string, typ godwarf.Type, pargFrameSize *int64) (*funcCallArg, error) {
	const CFA = 0x1000
	var off int64

	locprog, _, err := bi.locationExpr(entry, dwarf.AttrLocation, fn.Entry)
	if err != nil {
		err = fmt.Errorf("could not get argument location of %s: %v", argname, err)
	} else {
		var pieces []op.Piece
		off, pieces, err = op.ExecuteStackProgram(op.DwarfRegisters{CFA: CFA, FrameBase: CFA}, locprog, bi.Arch.PtrSize(), nil)
		if err != nil {
			err = fmt.Errorf("unsupported location expression for argument %s: %v", argname, err)
		}
		if pieces != nil {
			err = fmt.Errorf("unsupported location expression for argument %s (uses DW_OP_piece)", argname)
		}
		off -= CFA
	}
	if err != nil {
		// With Go version 1.12 or later we can trust that the arguments appear
		// in the same order as declared, which means we can calculate their
		// address automatically.
		// With this we can call optimized functions (which sometimes do not have
		// an argument address, due to a compiler bug) as well as runtime
		// functions (which are always optimized).
		off = *pargFrameSize
		off = alignAddr(off, typ.Align())
	}

	if e := off + typ.Size(); e > *pargFrameSize {

View on GitHub (pinned to a23773e6c3)

Solutions

1. Rebuild unoptimized so the compiler emits simple FB-relative argument locations
2. Use a newer Delve version with broader DWARF expression support
3. Avoid call injection on that function; use print/inspect instead

if err != nil && strings.Contains(err.Error(), "unsupported location expression") {
    // disable call injection for this target, use print instead
}

When it happens

Trigger: Old-ABI call injection where an argument's DW_AT_location expression contains unsupported DWARF opcodes or references registers/values unavailable in the synthetic DwarfRegisters context.

Common situations: Toolchain-generated complex location expressions (TLS-relative, indexed) that op.ExecuteStackProgram cannot evaluate with the synthetic CFA context used for argument layout.

Related errors

• could not get argument location of %s: %v
• could not find DIE for function %q
• DWARF read error: %v
• unsupported location expression for argument %s (uses DW_OP_
• unable to find function context

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/f27309e660e30cc7. Report an issue: GitHub.