go-delve/delve · error

could not get return values: %v

Error message

could not get return values: %v

What it means

Once the injected call returns, Delve builds a scope at the thread's current position to read return values. This error is raised when ThreadScope fails, i.e. the post-call frame could not be resolved, so the call's return values cannot be reported.

Source

Thrown at pkg/proc/fncall.go:896

			// See https://github.com/go-delve/delve/issues/2985 and
			// TestCallInjectionFlagCorruption
			rflags := bi.Arch.RegistersToDwarfRegisters(0, fncall.savedRegs).Uint64Val(regnum.AMD64_Rflags)
			err := thread.SetReg(regnum.AMD64_Rflags, op.DwarfRegisterFromUint64(rflags))
			if err != nil {
				fncall.err = fmt.Errorf("could not restore RFLAGS register: %v", err)
			}
		}
		return true

	case debugCallRegReadReturn: // 1
		// read return arguments from stack
		stack.callInjectionContinue = true
		if fncall.panicvar != nil || fncall.err != nil {
			break
		}
		retScope, err := ThreadScope(p, thread)
		if err != nil {
			fncall.err = fmt.Errorf("could not get return values: %v", err)
			break
		}

		// pretend we are still inside the function we called
		fakeFunctionEntryScope(retScope, fncall.fn, int64(regs.SP()), regs.SP()-uint64(bi.Arch.PtrSize()))
		var flags localsFlags
		flags |= localsNoDeclLineCheck | localsFakeFunctionEntryScope // if the function we are calling is an autogenerated stub then declaration lines have no meaning
		if !bi.regabi {
			flags |= localsTrustArgOrder
		}

		fncall.retvars, err = retScope.Locals(flags, "")
		if err != nil {
			fncall.err = fmt.Errorf("could not get return values: %v", err)
			break
		}
		fncall.retvars = filterVariables(fncall.retvars, func(v *Variable) bool {
			return (v.Flags & VariableReturnArgument) != 0

View on GitHub (pinned to a23773e6c3)

Solutions

1. Ensure the binary keeps full debug info (build without -ldflags '-s -w')
2. Check whether the called function terminated the process (e.g. os.Exit) — that's a legitimate failure mode
3. Retry the call at a different, symbolized stop location
4. Upgrade Go/Delve if the return frame is in runtime code with bad info

// Build with full debug info so the return frame resolves:
// go build -gcflags="all=-N -l" -o app .   # no -s -w stripping

err := dbg.CallFunction(scope, fn, args)
if err != nil && strings.Contains(err.Error(), "could not get return values") {
	// return frame unresolvable: retry or inspect state manually
}

When it happens

Trigger: funcCallStep in debugCallRegReadReturn (1), with no panic or earlier error, calls ThreadScope(p, thread) and it fails (symbolization failure at the return PC, dead thread, unreadable memory).

Common situations: Binary stripped of DWARF info; return PC lands in code without line info; process exited because the called function terminated it; optimized code confusing frame resolution.

Related errors

• no goroutine selected
• not implemented: %s
• could not get precheck error reason: %v
• %v
• could not restore registers: %v

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/41943d37777aeefa. Report an issue: GitHub.