From f1a72f8f11617390b8d3f68c339677fb403f0360 Mon Sep 17 00:00:00 2001
From: kilian-ai <kilian@voneu.co>
Date: Tue, 29 Sep 2026 12:04:40 -0700
Subject: [PATCH] wasm: build usr/gen_init_cpio on macOS hosts

Darwin lacks copy_file_range() and O_LARGEFILE, so the gen_init_cpio
host program fails to build and a macOS build of vmlinux.wasm stops in
usr/. Force-include a small compat header for that host program on
Darwin only: copy_file_range() becomes a read/write loop with the same
return contract, and O_LARGEFILE is 0 (off_t is already 64-bit there).
Other hosts are unchanged.

Tested on macOS 26 (Apple Silicon) with GNU Make 4.4.1 and Homebrew
LLVM 19.1.7 (matching flake.nix): defconfig + vmlinux.wasm builds on
top of f2a512c0d4a3, which no longer needs scripts/mod.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 arch/wasm/scripts/macos-host-compat.h | 48 +++++++++++++++++++++++++++
 usr/Makefile                          |  4 +++
 2 files changed, 52 insertions(+)
 create mode 100644 arch/wasm/scripts/macos-host-compat.h

diff --git a/arch/wasm/scripts/macos-host-compat.h b/arch/wasm/scripts/macos-host-compat.h
new file mode 100644
index 00000000000000..f5976634d79245
--- /dev/null
+++ b/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
diff --git a/usr/Makefile b/usr/Makefile
index e8f42478a0b765..7ae048c8d74c5c 100644
--- a/usr/Makefile
+++ b/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 :=