wasm: build usr/gen_init_cpio on macOS hosts

arch/wasm/scripts/macos-host-compat.h

@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Host-tool compatibility for building the wasm kernel on a macOS host.
+ * Included via -include for usr/gen_init_cpio only (see usr/Makefile).
+ * Darwin has neither O_LARGEFILE (files are always large-file capable)
+ * nor copy_file_range(); provide a plain read/write loop with the same
+ * contract gen_init_cpio relies on (returns bytes copied, -1 on error).
+ */
+#ifndef _WASM_MACOS_HOST_COMPAT_H
+#define _WASM_MACOS_HOST_COMPAT_H
+#ifdef __APPLE__
+#include <sys/types.h>
+#include <unistd.h>
+#include <errno.h>
+#ifndef O_LARGEFILE
+#define O_LARGEFILE 0
+#endif
+static inline ssize_t copy_file_range(int fd_in, off_t *off_in, int fd_out,
+				      off_t *off_out, size_t len, unsigned int flags)
+{
+	char buf[65536];
+	size_t total = 0;
+	(void)off_in; (void)off_out; (void)flags;
+	while (total < len) {
+		size_t want = len - total < sizeof(buf) ? len - total : sizeof(buf);
+		ssize_t n = read(fd_in, buf, want);
+		if (n < 0) {
+			if (errno == EINTR)
+				continue;
+			return total ? (ssize_t)total : -1;
+		}
+		if (n == 0)
+			break;
+		for (ssize_t done = 0; done < n;) {
+			ssize_t w = write(fd_out, buf + done, n - done);
+			if (w < 0) {
+				if (errno == EINTR)
+					continue;
+				return -1;
+			}
+			done += w;
+		}
+		total += n;
+	}
+	return total;
+}
+#endif /* __APPLE__ */
+#endif

usr/Makefile

@@ -17,6 +17,10 @@ obj-$(CONFIG_BLK_DEV_INITRD) := initramfs_data.o
 $(obj)/initramfs_data.o: $(obj)/initramfs_inc_data
 
 hostprogs := gen_init_cpio
+# macOS hosts lack copy_file_range()/O_LARGEFILE; see the compat header.
+ifeq ($(shell uname -s),Darwin)
+HOSTCFLAGS_gen_init_cpio.o += -include $(srctree)/arch/wasm/scripts/macos-host-compat.h
+endif
 
 ramfs-input := $(CONFIG_INITRAMFS_SOURCE)
 cpio-data :=