1 files changed, 66 insertions, 0 deletions
diff --git a/common/image.c b/common/image.c
new file mode 100644
index 0000000..d114c6a
--- /dev/null
+++ b/common/image.c
@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * image.c - arm64 kernel Image validation and placement.
+ *
+ * The relocation rules are the ones from the kernel boot protocol,
+ * including the pre a2c1d73b94ed fallback where image_size is 0 and
+ * the offset was fixed. qemu virt loads us at the bottom of RAM, same
+ * place the kernel wants to be, so the common case is a no move.
+ *
+ * Copyright (C) 2026 Bradley Morgan <brads@mainlining.org>
+ */
+
+#include <string.h>
+#include <sys/types.h>
+#include <stdint.h>
+#include <boot.h>
+#include <endian.h>
+
+#define SZ_2M		0x200000UL
+#define SZ_16M		0x1000000UL
+#define IMAGE_OFFSET_FIXUP	0x80000ULL
+
+int tb_image_setup(uintptr_t image, uintptr_t mem_base, uint32 mem_size,
+		   struct tb_image *img)
+{
+	struct Image_header *ih = (struct Image_header *)image;
+	uint64_t image_size;
+	uint64_t text_offset;
+	uintptr_t dst;
+
+	if (le32_to_cpu(ih->magic) != LINUX_ARM64_IMAGE_MAGIC)
+		return -1;
+
+	if (le64_to_cpu(ih->image_size) == 0) {
+		/* ancient image, no size field, assume the old defaults */
+		image_size = SZ_16M;
+		text_offset = IMAGE_OFFSET_FIXUP;
+	} else {
+		image_size = le64_to_cpu(ih->image_size);
+		text_offset = le64_to_cpu(ih->text_offset);
+	}
+
+	if (image_size > mem_size)
+		return -1;
+
+	/*
+	 * flag bit 3 says the image can live anywhere, honour where it
+	 * already is. otherwise the base must be 2MB aligned, the
+	 * physical offset from there is text_offset.
+	 */
+	if (le64_to_cpu(ih->flags) & (1ULL << 3))
+		dst = image - text_offset;
+	else
+		dst = mem_base;
+
+	/* the whole image, header included, sits here, and code0 at its
+	 * start is the first instruction executed */
+	img->load = ((dst + SZ_2M - 1) & ~(uintptr_t)(SZ_2M - 1)) + text_offset;
+	img->ep = img->load;
+	img->size = image_size;
+
+	if (dst + image_size > mem_base + mem_size)
+		return -1;
+
+	return 0;
+}