Copyright 2018 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.
+build darwin openbsd,amd64 openbsd,arm64

package runtime

import
Call fn with arg as its argument. Return what fn returns. fn is the raw pc value of the entry point of the desired function. Switches to the system stack, if not already there. Preserves the calling point as the location where a profiler traceback will begin.go:nosplit
Leave caller's PC/SP/G around for traceback.
	 := getg()
	var  *m
	if  != nil {
		 = .m
	}
	if  != nil && .libcallsp == 0 {
		.libcallg.set()
sp must be the last, because once async cpu profiler finds all three values to be non-zero, it will use them
		.libcallsp = getcallersp()
Make sure we don't reset libcallsp. This makes libcCall reentrant; We remember the g/pc/sp for the first call on an M, until that libcCall instance returns. Reentrance only matters for signals, as libc never calls back into Go. The tricky case is where we call libcX from an M and record g/pc/sp. Before that call returns, a signal arrives on the same M and the signal handling code calls another libc function. We don't want that second libcCall from within the handler to be recorded, and we don't want that call's completion to zero libcallsp. We don't need to set libcall* while we're in a sighandler (even if we're not currently in libc) because we block all signals while we're handling a signal. That includes the profile signal, which is the one that uses the libcall* info.
		 = nil
	}
	 := asmcgocall(, )
	if  != nil {
		.libcallsp = 0
	}
	return