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

-- expect --
SUCCESS
-- trace --
Trace Go1.22
EventBatch gen=1 m=0 time=0 size=23
ProcStatus dt=1 p=1 pstatus=2
ProcStatus dt=1 p=0 pstatus=1
GoStatus dt=1 g=1 m=0 gstatus=2
GoSyscallBegin dt=1 p_seq=1 stack=0
ProcStart dt=1 p=1 p_seq=1
GoSyscallEndBlocked dt=1
EventBatch gen=1 m=1 time=0 size=14
ProcStatus dt=1 p=2 pstatus=1
GoStatus dt=1 g=2 m=1 gstatus=2
ProcSteal dt=1 p=0 p_seq=2 m=0
EventBatch gen=1 m=18446744073709551615 time=0 size=5

	b0.Event("ProcStatus", trace.ProcID(1), go122.ProcIdle)
	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("ProcStart", trace.ProcID(1), testgen.Seq(1))
	b0.Event("GoSyscallEndBlocked")

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

	// on that P.
	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("ProcSteal", trace.ProcID(0), testgen.Seq(2), trace.ThreadID(0))
	b0.Event("ProcStart", trace.ProcID(0), testgen.Seq(3))
	b0.Event("GoSyscallEndBlocked")

	b0.Event("ProcStatus", trace.ProcID(1), go122.ProcIdle)
	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("ProcStart", trace.ProcID(1), testgen.Seq(1))
	b0.Event("GoSyscallEndBlocked")

	// A running goroutine steals proc 0.
	b1 := g.Batch(trace.ThreadID(1), 0)

GoSyscallBegin dt=11 p_seq=22 stack=7
GoSyscallEnd dt=177
GoSyscallBegin dt=14 p_seq=23 stack=7
GoSyscallEnd dt=62
GoSyscallBegin dt=13 p_seq=24 stack=7
GoSyscallEnd dt=90
GoSyscallBegin dt=11 p_seq=25 stack=7
GoSyscallEnd dt=69
GoSyscallBegin dt=13 p_seq=26 stack=7
GoSyscallEnd dt=65
GoSyscallBegin dt=15 p_seq=27 stack=7
GoSyscallEnd dt=72
GoSyscallBegin dt=15 p_seq=28 stack=7
GoSyscallEnd dt=73

	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("GoDestroySyscall")

	// A new Go-created thread with the same ID appears and
	// starts running, then tries to steal the P from the

HeapAlloc dt=87 heapalloc_value=26484360
GoSyscallBegin dt=18 p_seq=16 stack=67
GoSyscallEnd dt=456
GoSyscallBegin dt=41 p_seq=17 stack=68
GoSyscallEnd dt=25
GoSyscallBegin dt=16 p_seq=18 stack=69
GoSyscallEnd dt=18
HeapAlloc dt=193 heapalloc_value=26549896
GoSyscallBegin dt=69 p_seq=19 stack=70
GoSyscallEnd dt=227
GoSyscallBegin dt=12 p_seq=20 stack=70
GoSyscallEnd dt=105
GoSyscallBegin dt=87 p_seq=21 stack=71
GoSyscallEnd dt=48

	// traceProcSyscall. It's used in the very specific case
	// where the first a P is mentioned in a generation is
	// part of a ProcSteal event. If that's the first time
	// it's mentioned, then there's no GoSyscallBegin to
	// connect the P stealing back to at that point. This
	// special state indicates this to the parser, so it
	// doesn't try to find a GoSyscallEndBlocked that
	// corresponds with the ProcSteal.

		// We can fix this by acquiring the goroutine's scan bit.
		w = w.writeGoStatus(gp.goid, -1, traceGoWaiting, gp.inMarkAssist, 0)
	}
	return w
}

// GoSysCall emits a GoSyscallBegin event.
//
// Must be called with a valid P.
func (tl traceLocker) GoSysCall() {
	// Scribble down the M that the P is currently attached to.
	pp := tl.mp.p.ptr()
	pp.trace.mSyscallID = int64(tl.mp.procid)