Use libc to free pointer, closes #1

libc.go

@@ -0,0 +1,16 @@
+//go:build darwin
+// +build darwin
+
+package launchd
+
+import "unsafe"
+
+// free is defined in libxpc.dylib
+var libc_free_trampoline_addr uintptr
+
+//go:cgo_import_dynamic libc_free free "/usr/lib/libSystem.B.dylib"
+
+//go:nosplit
+func free(ptr unsafe.Pointer) {
+	syscall_syscall(libc_free_trampoline_addr, uintptr(ptr), 0, 0)
+}

libc.s

@@ -0,0 +1,13 @@
+//go:build darwin
+// +build darwin
+
+#include "textflag.h"
+
+// The trampolines are ABIInternal as they are address-taken in
+// Go code.
+
+TEXT libc_free_trampoline<>(SB),NOSPLIT,$0-0
+    JMP	libc_free(SB)
+
+GLOBL	·libc_free_trampoline_addr(SB), RODATA, $8
+DATA	·libc_free_trampoline_addr(SB)/8, $libc_free_trampoline<>(SB)

libxpc.go

@@ -27,7 +27,12 @@ func libxpc_launch_activate_socket(name string) ([]int, error) {
 		return nil, err
 	}
 	var c_fds_ptr *uintptr // *C.int
-	var c_cnt uint         // C.size_t
+	defer func() {
+		if c_fds_ptr != nil {
+			free(unsafe.Pointer(c_fds_ptr))
+		}
+	}()
+	var c_cnt uint // C.size_t
 	res, _, _ := syscall_syscall(
 		libxpc_launch_activate_socket_trampoline_addr,
 		uintptr(unsafe.Pointer(c_name_ptr)),
@@ -41,7 +46,6 @@ func libxpc_launch_activate_socket(name string) ([]int, error) {
 		return nil, syscall.EINVAL
 	}
 	c_fds := (*[maxFDs]int)(unsafe.Pointer(c_fds_ptr))
-	// TODO: free c_fds_ptr after copy?
 	fds := make([]int, c_cnt)
 	copy(fds, (*c_fds)[0:c_cnt])
 	return fds, nil