tashaboot: arm64 bootloaderHEADmain

holy shit it's here, Tashaboot, based from arm arm, enjoy
reading this masterpiece

Signed-off-by: Bradley Morgan <brads@mainlining.org>

1 files changed, 77 insertions, 0 deletions

diff --git a/common/image.c b/common/image.c
new file mode 100644
index 0000000..640eab4
--- /dev/null
+++ b/common/image.c
@@ -0,0 +1,77 @@
+/* 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 quirks, same math u-boot's
+ * booti_setup() runs.
+ *
+ * Copyright (C) 2026 Bradley Morgan <brads@mainlining.org>
+ */
+
+#include <stdint.h>
+#include <string.h>
+#include <endian.h>
+#include <boot.h>
+
+#define LINUX_ARM64_IMAGE_MAGIC	0x644d5241	/* "ARM\x64" */
+
+#define SZ_16M			0x01000000
+#define SZ_2M			0x00200000
+
+/* the 64 byte header from Documentation/arch/arm64/booting.rst */
+struct Image_header {
+	uint32 code0;		/* executable */
+	uint32 code1;		/* unused */
+	uint64 text_offset;	/* load offset, LE */
+	uint64 image_size;	/* size, LE */
+	uint64 flags;		/* bit 3: relocatable */
+	uint64 res1;
+	uint64 res2;
+	uint64 res3;
+	uint32 magic;		/* "ARM\x64" */
+	uint32 res4;
+};
+
+int tb_image_setup(uintptr_t image, struct tb_image *img)
+{
+	const struct Image_header *ih = (const struct Image_header *)image;
+	uint64_t image_size, text_offset;
+
+	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 = 0x80000;
+	} else {
+		image_size = le64_to_cpu(ih->image_size);
+		text_offset = le64_to_cpu(ih->text_offset);
+	}
+
+	/*
+	 * 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)) {
+		uintptr_t base = image - text_offset;
+
+		img->load = ((base + SZ_2M - 1) & ~(uintptr_t)(SZ_2M - 1)) +
+			    text_offset;
+	} else {
+		/*
+		 * no relocate flag: the image must sit text_offset from a
+		 * 2MB aligned base. it is already staged at the fixed
+		 * address, treat its own position as the answer.
+		 */
+		img->load = image;
+	}
+
+	/* the whole image, header included, lives at load, entry is code0 */
+	img->ep = img->load;
+	img->size = image_size;
+
+	return 0;
+}