bsps/aarch64/start: Add support for Image protocol

This adds support for a the Image header protocol similar to the zImage
protocol that Linux kernels use to describe their expectations of the
system configuration.

bsps/aarch64/shared/start/start.S

@@ -37,12 +37,35 @@
 #include <rtems/asm.h>
 #include <rtems/score/percpu.h>
 
+#include <bsp.h>
 #include <bspopts.h>
 
   /* Global symbols */
   .globl _start
   .section ".bsp_start_text", "ax"
 
+#ifdef BSP_START_IMAGE_HEADER
+  /*
+   * This format is defined by:
+   * https://www.kernel.org/doc/Documentation/arm64/booting.txt
+   */
+  mov	x0, x0
+  b	_start
+  /*
+   * This must be defined by the BSP as different environments may not treat it
+   * the same. Xen treats it as an offset from 0x40000000 while QEMU treats it
+   * as an absolute offset (RAM origin + load offset).
+   */
+  .dword  BSP_START_IMAGE_HEADER_LOAD_OFFSET
+  .dword  0 /* image size */
+  .dword  0 /* kernel flags, LE, page size unspecified, place near RAM start */
+  .dword  0 /* reserved 2 */
+  .dword  0 /* reserved 3 */
+  .dword  0 /* reserved 4 */
+  .word   0x644d5241 /* magic, ascii ['A', 'R', 'M', 64] LE */
+  .word   0 /* reserved 5, PE COFF offset */
+#endif /* BSP_START_IMAGE_HEADER */
+
 /* Start entry */
 
 _start:

spec/build/bsps/aarch64/optimghdr.yml

@@ -0,0 +1,16 @@
+SPDX-License-Identifier: CC-BY-SA-4.0 OR BSD-2-Clause
+actions:
+- get-boolean: null
+- define-condition: null
+build-type: option
+copyrights:
+- Copyright (C) 2025 On-Line Applications Research (OAR)
+default:
+- enabled-by: true
+  value: true
+description: |
+  include zImage boot header
+enabled-by: true
+links: []
+name: BSP_START_IMAGE_HEADER
+type: build