go-delve/delve · error

CFA becomes undefined at PC %#x: %v

Error message

CFA becomes undefined at PC %#x: %v

What it means

While unwinding via DWARF CFI, Delve evaluates the CFA (Canonical Frame Address) rule at the current PC. If the rule evaluates to nil/undefined (and err carries the reason), the caller's frame address cannot be computed and unwinding aborts. This means the binary's DWARF frame information is missing or inapplicable at that PC.

Source

Thrown at pkg/proc/stack.go:724

	logger := logflags.StackLogger()

	fde, err := it.bi.frameEntries.FDEForPC(it.pc)
	var framectx *frame.FrameContext
	if _, nofde := err.(*frame.ErrNoFDEForPC); nofde {
		framectx = it.bi.Arch.fixFrameUnwindContext(nil, it.pc, it.bi)
	} else {
		fctxt, err := fde.EstablishFrame(it.pc)
		if err != nil {
			logger.Errorf("Error executing Frame Debug Entry for PC %x: %v", it.pc, err)
		}
		framectx = it.bi.Arch.fixFrameUnwindContext(fctxt, it.pc, it.bi)
	}

	logger.Debugf("advanceRegs (DWARF) at %#x", it.pc)

	cfareg, err := it.executeFrameRegRule(0, framectx.CFA, 0)
	if cfareg == nil {
		it.err = fmt.Errorf("CFA becomes undefined at PC %#x: %v", it.pc, err)
		return op.DwarfRegisters{}, 0, 0
	}
	if logflags.Stack() {
		logger.Debugf("\tCFA rule %s -> %#x", ruleString(&framectx.CFA, it.bi.Arch.RegnumToString), cfareg.Uint64Val)
	}
	it.regs.CFA = int64(cfareg.Uint64Val)

	callimage := it.bi.PCToImage(it.pc)

	callFrameRegs = op.DwarfRegisters{
		StaticBase: callimage.StaticBase,
		ByteOrder:  it.regs.ByteOrder,
		PCRegNum:   it.regs.PCRegNum,
		SPRegNum:   it.regs.SPRegNum,
		BPRegNum:   it.regs.BPRegNum,
		LRRegNum:   it.regs.LRRegNum,
	}

View on GitHub (pinned to a23773e6c3)

Solutions

1. Rebuild the target ensuring debug info is present (default `go build`, no -s -w)
2. Update Delve; it ships fallback heuristics for Go runtime assembly frames
3. Use the fallback stack unwinding (check frame-architecture assumptions) or stop the walk before foreign frames
4. Verify you attached to the exact binary matching the loaded image addresses

Example fix

// before
go build -ldflags="-s -w" -o app .
// after
go build -o app .

if _, ok := bi.frameDescriptionForPC(pc); !ok { /* no FDE at pc: expect undefined CFA */ }

_, err := iterateFrames(); if err != nil && strings.Contains(err.Error(), "CFA becomes undefined") { /* stop the walk and present frames collected so far */ }

When it happens

Trigger: advanceRegs (DWARF path) executed at a PC where no FDE/rule covers the CFA — e.g. unwinding into code without DWARF frame info (assembly runtime functions, JIT, or foreign code) or truncated .debug_frame/.eh_frame.

Common situations: Stacks crossing from Go code into hand-written assembly or system libraries without DWARF; binaries built with frame info stripped; mixing a binary and a debug-info mismatch (wrong binary loaded at address).

Related errors

• Undefined return address at %#x
• could not retrieve CFA for current PC
• unexpected CFA rule %d at uprobe PC %#x
• ErrStackUnderflow
• ErrStackIndexOutOfBounds

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/7a5ccdc0d8a30ac9. Report an issue: GitHub.