go-delve/delve · error

start address(%x) should be less than end address(%x)

Error message

start address(%x) should be less than end address(%x)

What it means

proc.Disassemble disassembles machine code in the address range [startAddr, endAddr) of the target's memory. It rejects calls where startAddr > endAddr with this error, because a reversed range is meaningless and downstream code allocates a buffer of size startAddr-endAddr. Equal addresses are allowed and yield an empty instruction list.

Source

Thrown at pkg/proc/disasm.go:125

func checkPrologue(s []AsmInstruction, prologuePattern opcodeSeq) bool {
	line := s[0].Loc.Line
	for i, op := range prologuePattern {
		if !s[i].Inst.OpcodeEquals(op) || s[i].Loc.Line != line {
			return false
		}
	}
	return true
}

// Disassemble disassembles target memory between startAddr and endAddr, marking
// the current instruction being executed in goroutine g.
// If currentGoroutine is set and thread is stopped at a CALL instruction Disassemble
// will evaluate the argument of the CALL instruction using the thread's registers.
// Be aware that the Bytes field of each returned instruction is a slice of a larger array of size startAddr - endAddr.
func Disassemble(mem MemoryReadWriter, regs Registers, breakpoints *BreakpointMap, bi *BinaryInfo, startAddr, endAddr uint64) ([]AsmInstruction, error) {
	if startAddr > endAddr {
		return nil, fmt.Errorf("start address(%x) should be less than end address(%x)", startAddr, endAddr)
	}
	return disassemble(mem, regs, breakpoints, bi, startAddr, endAddr, false)
}

func disassemble(memrw MemoryReadWriter, regs Registers, breakpoints *BreakpointMap, bi *BinaryInfo, startAddr, endAddr uint64, singleInstr bool) ([]AsmInstruction, error) {
	var dregs *op.DwarfRegisters
	if regs != nil {
		dregs = bi.Arch.RegistersToDwarfRegisters(0, regs)
	}

	mem := make([]byte, int(endAddr-startAddr))
	_, err := memrw.ReadMemory(mem, startAddr)
	if err != nil {
		return nil, err
	}

	r := make([]AsmInstruction, 0, len(mem)/bi.Arch.MaxInstructionLength())
	pc := startAddr

View on GitHub (pinned to a23773e6c3)

Solutions

1. Swap the arguments so startAddr is the lower address (e.g. min/max the two values).
2. Check where the bounds are computed (e.g. fn.Entry/fn.End from the symbol table) and fix the reversal or underflow.
3. For RPC/DAP clients, verify the Start and End fields sent in the request are ordered ascending.
4. Add a guard before calling: only invoke when endAddr > startAddr, else return an empty result.

Example fix

// before
insns, err := proc.Disassemble(mem, regs, bp, bi, fn.End, fn.Entry) // swapped

// after
insns, err := proc.Disassemble(mem, regs, bp, bi, fn.Entry, fn.End)

func safeDisassemble(mem proc.MemoryReadWriter, regs proc.Registers, bp *proc.BreakpointMap, bi *proc.BinaryInfo, start, end uint64) ([]proc.AsmInstruction, error) {
    if start > end {
        start, end = end, start
    }
    return proc.Disassemble(mem, regs, bp, bi, start, end)
}

func validRange(start, end uint64) bool {
    return start <= end
}

insns, err := proc.Disassemble(mem, regs, bp, bi, startAddr, endAddr)
if err != nil {
    if strings.Contains(err.Error(), "should be less than end address") {
        startAddr, endAddr = endAddr, startAddr
        insns, err = proc.Disassemble(mem, regs, bp, bi, startAddr, endAddr)
    }
    if err != nil { return nil, err }
}

When it happens

Trigger: Calling proc.Disassemble (or its public callers findRetPC, setStepIntoNewProcBreakpoint, skipAutogeneratedWrappersIn, and service-level StepInto/Disassemble RPC/DAP requests) with swapped or computed bounds such that startAddr > endAddr.

Common situations: A client computing a function's range from a symbol table with reversed hi/lo bounds; endAddr computed as funcEnd - n with unsigned underflow; an RPC client sending incorrectly ordered Start/End arguments.

Related errors

• clear-checkpoint argument must be a checkpoint ID
• too many arguments
• wrong number of arguments to "config"
• could not find CALL instruction for address %#x in %s
• wrong argument: %q is not a number

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/b4e55bca3c409693. Report an issue: GitHub.