func gcStart(trigger gcTrigger) {
	// Since this is called from malloc and malloc is called in
	// the guts of a number of libraries that might be holding
	// locks, don't attempt to start GC in non-preemptible or
	// potentially unstable situations.
	mp := acquirem()
	if gp := getg(); gp == mp.g0 || mp.locks > 1 || mp.preemptoff != "" {
		releasem(mp)
		return
	}
	releasem(mp)
	mp = nil

// weight allocation. If it is a heavy weight allocation the caller must
// determine whether a new GC cycle needs to be started or if the GC is active
// whether this goroutine needs to assist the GC.
//
// Must run in a non-preemptible context since otherwise the owner of
// c could change.
func (c *mcache) nextFree(spc spanClass) (v gclinkptr, s *mspan, shouldhelpgc bool) {
	s = c.alloc[spc]
	shouldhelpgc = false
	freeIndex := s.nextFreeIndex()

	} else {
		return uint(i) & (1<<arenaL2Bits - 1)
	}
}

// inheap reports whether b is a pointer into a (potentially dead) heap object.
// It returns false for pointers into mSpanManual spans.
// Non-preemptible because it is used by write barriers.
//
//go:nowritebarrier
//go:nosplit
func inheap(b uintptr) bool {
	return spanOfHeap(b) != nil
}

	// before we get here (after the transfer out) but that's OK: that new
	// P won't be in the ProcSyscall state anymore.
	//
	// Basically: while we have a preemptible P, don't advance, because we
	// *know* from the event that we're going to lose it at some point during
	// the syscall. We shouldn't advance until that happens.
	if curCtx.P != NoProc {
		pState, ok := o.pStates[curCtx.P]