//
// fpunwindExpand checks if pcBuf contains logical frames (which include inlined
// frames) or physical frames (produced by frame pointer unwinding) using a
// sentinel value in pcBuf[0]. Logical frames are simply returned without the
// sentinel. Physical frames are turned into logical frames via inline unwinding
// and by applying the skip value that's stored in pcBuf[0].
func fpunwindExpand(dst, pcBuf []uintptr) int {
	if len(pcBuf) == 0 {

			// We're probably in the trailing function padding, where findfunc
			// still returns f but there's no symbolic information. Just keep
			// going until we definitely hit the end. If we see a "?" in the
			// middle of unwinding, that's a real problem.
			//
			// TODO: If we ever have function end information, use that to make
			// this robust.
			continue
		}
		for ; uf.valid(); uf = u.next(uf) {
			file, line := u.fileLine(uf)

		pc := c.pc()
		sp := c.sp()

		// If we don't recognize the PC as code
		// but we do recognize the top pointer on the stack as code,
		// then assume this was a call to non-code and treat like
		// pc == 0, to make unwinding show the context.
		if pc != 0 && !findfunc(pc).valid() && findfunc(*(*uintptr)(unsafe.Pointer(sp))).valid() {
			pc = 0
		}

		// IF LR exists, sigpanictramp must save it to the stack

		// here we'll see a seemingly self-recursive call, which is in
		// fact not.
		// This is normally ok, as we use the return address saved on
		// stack for unwinding, not the LR value. But if this is a
		// call to morestack, we haven't created the frame, and we'll
		// use the LR for unwinding, which will be bad.
		return false, 0
	}
	up, startpc := pcdatavalue2(f, abi.PCDATA_UnsafePoint, pc)
	if up == abi.UnsafePointUnsafe {

	// and String methods to prepare the panic strings before startpanic.
	preprintpanics(&p)

	fatalpanic(&p)   // should not return
	*(*int)(nil) = 0 // not reached
}

// start initializes a panic to start unwinding the stack.
//
// If p.goexit is true, then start may return multiple times.
func (p *_panic) start(pc uintptr, sp unsafe.Pointer) {
	gp := getg()

	// Record the caller's PC and SP, so recovery can identify panics

// Then it calls _cgoexp_GoF(frame).
//
// _cgoexp_GoF, which was generated by cmd/cgo, unpacks the arguments
// from frame, calls p.GoF, writes the results back to frame, and
// returns. Now we start unwinding this whole process.
//
// runtime.cgocallbackg pops but does not execute the deferred
// function to unwind m.g0.sched.sp, calls runtime.entersyscall, and
// returns to runtime.cgocallback.
//

	BNE	store64loop

	DMB	MB_ISH
	RET

// The following functions all panic if their address argument isn't
// 8-byte aligned. Since we're calling back into Go code to do this,
// we have to cooperate with stack unwinding. In the normal case, the
// functions tail-call into the appropriate implementation, which
// means they must not open a frame. Hence, when they go down the
// panic path, at that point they push the LR to create a real frame

}

// cheaprand is a non-cryptographic-quality 32-bit random generator
// suitable for calling at very high frequency (such as during scheduling decisions)
// and at sensitive moments in the runtime (such as during stack unwinding).
// it is "cheap" in the sense of both expense and quality.
//
// cheaprand must not be exported to other packages:
// the rule is that other packages using runtime-provided
// randomness must always use rand.
//

	//
	// If neither unwindPrintErrors or unwindSilentErrors are set, unwinding
	// performs extra consistency checks and throws on any error.
	//
	// Note that there are a small number of fatal situations that will throw
	// regardless of unwindPrintErrors or unwindSilentErrors.
	unwindPrintErrors unwindFlags = 1 << iota

	// unwindSilentErrors silently ignores errors during unwinding.
	unwindSilentErrors

	tracefpunwindoff: setting tracefpunwindoff=1 forces the execution tracer to
	use the runtime's default stack unwinder instead of frame pointer unwinding.
	This increases tracer overhead, but could be helpful as a workaround or for
	debugging unexpected regressions caused by frame pointer unwinding.

	traceadvanceperiod: the approximate period in nanoseconds between trace generations. Only