runtime: darwin/arm64 c-archive entry point

Change-Id: Ib227aa3e14d01a0ab1ad9e53d107858e045d1c42
Reviewed-on: https://go-review.googlesource.com/8984Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/rt0_darwin_arm64.s

@@ -11,6 +11,40 @@ TEXT _rt0_arm64_darwin(SB),NOSPLIT,$-8
 	MOVD	$1, R16	// SYS_exit
 	SVC	$0x80
 
+// When linking with -buildmode=c-archive or -buildmode=c-shared,
+// this symbol is called from a global initialization function.
+//
+// Note that all currently shipping darwin/arm64 platforms require
+// cgo and do not support c-shared.
+TEXT _rt0_arm64_darwin_lib(SB),NOSPLIT,$0
+	// R27 is REGTMP, reserved for liblink. It is used below to
+	// move R0/R1 into globals. However in the standard ARM64 calling
+	// convention, it is a callee-saved register. So we save it to a
+	// temporary register.
+	MOVD  R27, R7
+
+	MOVD  R0, _rt0_arm64_darwin_lib_argc<>(SB)
+	MOVD  R1, _rt0_arm64_darwin_lib_argv<>(SB)
+	// Create a new thread to do the runtime initialization and return.
+	MOVD  _cgo_sys_thread_create(SB), R4
+	MOVD  $_rt0_arm64_darwin_lib_go(SB), R0
+	MOVD  $0, R1
+	BL    (R4)
+
+	MOVD  R7, R27
+	RET
+
+TEXT _rt0_arm64_darwin_lib_go(SB),NOSPLIT,$0
+	MOVD  _rt0_arm64_darwin_lib_argc<>(SB), R0
+	MOVD  _rt0_arm64_darwin_lib_argv<>(SB), R1
+	MOVD  $runtime·rt0_go(SB), R4
+	B     (R4)
+
+DATA  _rt0_arm64_darwin_lib_argc<>(SB)/8, $0
+GLOBL _rt0_arm64_darwin_lib_argc<>(SB),NOPTR, $8
+DATA  _rt0_arm64_darwin_lib_argv<>(SB)/8, $0
+GLOBL _rt0_arm64_darwin_lib_argv<>(SB),NOPTR, $8
+
 TEXT main(SB),NOSPLIT,$-8
 	MOVD	$runtime·rt0_go(SB), R2
 	BL	(R2)