}
		case NonEqual_Fail:
			if po.NonEqual(v[op.a], v[op.b]) {
				t.Errorf("FAILED: op%d%v passed", idx, op)
			}
		case Checkpoint:
			po.Checkpoint()
		case Undo:
			t.Log("Undo stack", po.undo)
			po.Undo()
		default:
			panic("unimplemented")
		}

		if false {
			po.DotDump(fmt.Sprintf("op%d.dot", idx), fmt.Sprintf("Last op: %v", op))
		}

		po.CheckIntegrity()
	}

}

func TestStackOverflow(t *testing.T) {
	output := runTestProg(t, "testprog", "StackOverflow")
	want := []string{
		"runtime: goroutine stack exceeds 1474560-byte limit\n",
		"fatal error: stack overflow",
		// information about the current SP and stack bounds
		"runtime: sp=",
		"stack=[",
	}
	if !strings.HasPrefix(output, want[0]) {
		t.Errorf("output does not start with %q", want[0])
	}
	for _, s := range want[1:] {

		return "reflect: call of " + e.Method + " on zero Value"
	}
	return "reflect: call of " + e.Method + " on " + e.Kind.String() + " Value"
}

// methodName returns the name of the calling method,
// assumed to be two stack frames above.
func methodName() string {
	pc, _, _, _ := runtime.Caller(2)
	f := runtime.FuncForPC(pc)
	if f == nil {
		return "unknown method"
	}
	return f.Name()
}

package main

// This program failed when run under the C/C++ ThreadSanitizer. The
// TSAN library was not keeping track of whether signals should be
// delivered on the alternate signal stack, and the Go signal handler
// was not preserving callee-saved registers from C callers.

/*
#cgo CFLAGS: -g -fsanitize=thread
#cgo LDFLAGS: -g -fsanitize=thread

#include <stdlib.h>
#include <sys/time.h>

// run

// Copyright 2021 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This tickles a stack-allocation bug when the register ABI is enabled.
// The original report was from cue, internal/core/adt/equality.go,
// function equalVertex.

// In the failing case, something bad gets passed to equalTerminal.

package main

import "fmt"

//go:noinline
func recur(x int) {
	for i := 0; i < x; i++ {
		G = rec(i)
	}
}

func main() {
	b := newB(17)
	for _, opt := range ROSL {
		opt(b)
	}
	stop := b.startit()

	// see if we can get some stack growth/moving
	recur(10101)

	if stop != nil {
		stop <- struct{}{}
	}

	REGCTXT = REG_R26 // environment for closures
	REGTMP  = REG_R27 // reserved for liblink
	REGG    = REG_R28 // G
	REGFP   = REG_R29 // frame pointer
	REGLINK = REG_R30

	// ARM64 uses R31 as both stack pointer and zero register,
	// depending on the instruction. To differentiate RSP from ZR,
	// we use a different numeric value for REGZERO and REGSP.
	REGZERO = REG_R31
	REGSP   = REG_RSP

	FREGRET = REG_F0

	{11, "SIGSEGV", "segmentation fault"},
	{12, "SIGUSR2", "user defined signal 2"},
	{13, "SIGPIPE", "broken pipe"},
	{14, "SIGALRM", "alarm clock"},
	{15, "SIGTERM", "terminated"},
	{16, "SIGSTKFLT", "stack fault"},
	{17, "SIGCHLD", "child exited"},
	{18, "SIGCONT", "continued"},
	{19, "SIGSTOP", "stopped (signal)"},
	{20, "SIGTSTP", "stopped"},
	{21, "SIGTTIN", "stopped (tty input)"},

// interface to back end

type ArchInfo struct {
	LinkArch *obj.LinkArch

	REGSP     int
	MAXWIDTH  int64
	SoftFloat bool

	PadFrame func(int64) int64

	// ZeroRange zeroes a range of memory on stack. It is only inserted
	// at function entry, and it is ok to clobber registers.
	ZeroRange func(*objw.Progs, *obj.Prog, int64, int64, *uint32) *obj.Prog

	Ginsnop func(*objw.Progs) *obj.Prog

		cfg.CallTree = true
		cfg.Trim = false
		cfg.Granularity = "filefunctions"
	})
	if rpt == nil {
		return // error already reported
	}

	// Make stack data and generate corresponding JSON.
	stacks := rpt.Stacks()
	b, err := json.Marshal(stacks)
	if err != nil {
		http.Error(w, "error serializing stacks for flame graph",
			http.StatusInternalServerError)