// A goroutine gets created on a running P, then starts running.
	b0 := g1.Batch(trace.ThreadID(0), 0)
	b0.Event("ProcStatus", trace.ProcID(0), go122.ProcRunning)
	b0.Event("GoCreate", trace.GoID(5), testgen.NoStack, testgen.NoStack)
	b0.Event("GoStart", trace.GoID(5), testgen.Seq(1))
	b0.Event("GoStop", "whatever", testgen.NoStack)

	b0.Event("GoStatus", trace.GoID(1), trace.ThreadID(0), go122.GoRunning)
	b0.Event("GoSyscallBegin", testgen.Seq(1), testgen.NoStack)
	b0.Event("ProcStart", trace.ProcID(1), testgen.Seq(1))
	b0.Event("GoSyscallEndBlocked")

	// A running goroutine steals proc 0.
	b1 := g.Batch(trace.ThreadID(1), 0)
	b1.Event("ProcStatus", trace.ProcID(2), go122.ProcRunning)
	b1.Event("GoStatus", trace.GoID(2), trace.ThreadID(1), go122.GoRunning)

	b0 := g.Batch(trace.ThreadID(0), 0)
	b0.Event("GoCreateSyscall", trace.GoID(4))
	b0.Event("GoSyscallEndBlocked")
	b0.Event("ProcStatus", trace.ProcID(0), go122.ProcIdle)
	b0.Event("ProcStart", trace.ProcID(0), testgen.Seq(1))
	b0.Event("GoStatus", trace.GoID(4), trace.NoThread, go122.GoRunnable)
	b0.Event("GoStart", trace.GoID(4), testgen.Seq(1))
	b0.Event("GoSyscallBegin", testgen.Seq(2), testgen.NoStack)

	b0.Event("GoStatus", trace.GoID(1), trace.ThreadID(0), go122.GoRunning)
	b0.Event("GoSyscallBegin", testgen.Seq(1), testgen.NoStack)
	b0.Event("GoSyscallEndBlocked")

	// A running goroutine steals proc 0.
	b1 := g.Batch(trace.ThreadID(1), 0)
	b1.Event("ProcStatus", trace.ProcID(2), go122.ProcRunning)
	b1.Event("GoStatus", trace.GoID(2), trace.ThreadID(1), go122.GoRunning)

}

func gen(t *testgen.Trace) {
	g := t.Generation(1)

	// One goroutine is exiting with a syscall. It already
	// acquired a new P.
	b0 := g.Batch(trace.ThreadID(0), 0)
	b0.Event("GoStatus", trace.GoID(1), trace.ThreadID(0), go122.GoSyscall)
	b0.Event("ProcStatus", trace.ProcID(1), go122.ProcIdle)
	b0.Event("ProcStart", trace.ProcID(1), testgen.Seq(1))
	b0.Event("GoSyscallEndBlocked")

func gen(t *testgen.Trace) {
	g1 := t.Generation(1)

	// A running goroutine emits a task begin.
	b1 := g1.Batch(trace.ThreadID(0), 0)
	b1.Event("ProcStatus", trace.ProcID(0), go122.ProcRunning)
	b1.Event("GoStatus", trace.GoID(1), trace.ThreadID(0), go122.GoRunning)
	b1.Event("UserTaskBegin", trace.TaskID(2), trace.TaskID(0) /* 0 means no parent, not background */, "my task", testgen.NoStack)

	g2 := t.Generation(2)

	// One goroutine does a syscall without blocking, then another one where
	// it's P gets stolen.
	b0 := g.Batch(trace.ThreadID(0), 0)
	b0.Event("ProcStatus", trace.ProcID(0), go122.ProcRunning)
	b0.Event("GoStatus", trace.GoID(1), trace.ThreadID(0), go122.GoRunning)
	b0.Event("GoSyscallBegin", testgen.Seq(1), testgen.NoStack)
	b0.Event("GoSyscallEnd")
	b0.Event("GoSyscallBegin", testgen.Seq(2), testgen.NoStack)
	b0.Event("GoSyscallEndBlocked")

	// One goroutine is exiting with a syscall. It already
	// acquired a new P.
	b0 := g.Batch(trace.ThreadID(0), 0)
	b0.Event("ProcStatus", trace.ProcID(1), go122.ProcRunning)
	b0.Event("GoStatus", trace.GoID(1), trace.ThreadID(0), go122.GoSyscall)
	b0.Event("GoSyscallEndBlocked")

	// A bare M stole the goroutine's P at the generation boundary.
	b1 := g.Batch(trace.ThreadID(1), 0)

	// may be nil. Reporting goid of 0 is fine for either g0 or a nil gp.
	var hdr [3]uint64
	if pp != nil {
		// Overflow records in profBuf have all header values set to zero. Make
		// sure that real headers have at least one bit set.
		hdr[0] = uint64(pp.id)<<1 | 0b1
	} else {
		hdr[0] = 0b10
	}
	if gp != nil {
		hdr[1] = gp.goid
	}
	hdr[2] = uint64(mp.procid)

}

func gen(t *testgen.Trace) {
	g := t.Generation(1)

	// One goroutine enters a syscall.
	b0 := g.Batch(trace.ThreadID(0), 0)
	b0.Event("ProcStatus", trace.ProcID(0), go122.ProcRunning)
	b0.Event("GoStatus", trace.GoID(1), trace.ThreadID(0), go122.GoRunning)
	b0.Event("GoSyscallBegin", testgen.Seq(1), testgen.NoStack)
	b0.Event("GoSyscallEndBlocked")

	// A bare M steals the goroutine's P.
	b1 := g.Batch(trace.ThreadID(1), 0)