tashaboot: arm64 bringup, semihosting payload loader

consoles on the pl011 the dtb points at, walks the memory node and
chosen, loads an arm64 kernel Image over semihosting and jumps to it
with the documented register state. string functions, printf and
libfdt are vendored from lk (lk2nd) and u-boot so the libc surface is
the one those projects already proved. built and booted on qemu virt,
payload exits clean through semihosting.

1 files changed, 56 insertions, 0 deletions

diff --git a/include/boot.h b/include/boot.h
new file mode 100644
index 0000000..34bfa88
--- /dev/null
+++ b/include/boot.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __BOOT_H
+#define __BOOT_H
+
+#include <sys/types.h>
+#include <stdint.h>
+
+/*
+ * payload loading and the arm64 boot protocol. See Documentation/
+ * arch/arm64/booting.rst in the kernel tree for the register contract
+ * we honour when jumping.
+ */
+
+#define LINUX_ARM64_IMAGE_MAGIC	0x644d5241
+
+/* the 64 byte header every arm64 kernel Image starts with */
+struct Image_header {
+	uint32_t	code0;		/* Executable code */
+	uint32_t	code1;		/* Executable code */
+	uint64_t	text_offset;	/* Image load offset, LE */
+	uint64_t	image_size;	/* Effective Image size, LE */
+	uint64_t	flags;		/* Kernel flags, LE */
+	uint64_t	res2;		/* reserved */
+	uint64_t	res3;		/* reserved */
+	uint64_t	res4;		/* reserved */
+	uint32_t	magic;		/* Magic number */
+	uint32_t	res5;
+};
+
+struct tb_image {
+	uintptr_t	ep;		/* entry point to jump to */
+	uint64_t	size;		/* image size in bytes */
+	uintptr_t	load;		/* address the image was placed at */
+};
+
+/*
+ * validate the header at image and work out where it wants to live.
+ * returns 0 and fills img on success, negative on a bad image.
+ */
+int tb_image_setup(uintptr_t image, uintptr_t mem_base, uint32 mem_size,
+		   struct tb_image *img);
+
+/*
+ * load the payload from semihosting into mem_base. returns 0 and fills
+ * img, negative when there is no debugger or no file.
+ */
+int tb_load_semihosting(const char *fname, uintptr_t load_addr,
+			uintptr_t mem_base, uint32 mem_size,
+			struct tb_image *img);
+
+/*
+ * jump to the kernel: x0 = dtb, x1 = x2 = x3 = 0. never returns.
+ */
+void __NO_RETURN tb_boot_linux(uintptr_t ep, const void *dtb);
+
+#endif