arch: aarch64: Set up Stack Pointer

Introduce stack and bss memory regions, rename Start.S to start.S
This commit should allow jumping out of assembly code for certain
SoCs that had issues with SP like MTK and QCOM.

Signed-off-by: Ivaylo Ivanov <ivo.ivanov.ivanov1@gmail.com>

Makefile

@@ -340,8 +340,8 @@ endif # $(dot-config)
 all: arch/$(ARCH)/linker.lds uniLoader
 
 # List of main executables
-main-y		:= main/main.o
-main-y		+= arch/$(ARCH)/Start.o
+main-y		:= arch/$(ARCH)/start.o \
+		   main/main.o
 
 # Object directories
 objs-y		:= main

arch/Makefile

@@ -1 +1 @@
-obj-y += $(ARCH)/Start.o
+obj-y += $(ARCH)/start.o

arch/aarch64/Start.S

@@ -1,12 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-/*
- * Copyright (c) 2022, Ivaylo Ivanov <ivo.ivanov.ivanov1@gmail.com>
- */
-
-    adr	x0, dtb
-    adr	x1, kernel
-    b main
-
-.global load_kernel
-load_kernel:
-    br	x4

arch/aarch64/linker.lds.S

@@ -13,15 +13,30 @@ INPUT(DTB_PATH)
 SECTIONS
 {
 	.boot : {
-		arch/aarch64/Start.o
+		arch/aarch64/start.o
 	}
 
-	.dtb ALIGN(0x1000) : {
+	.text : {
+		*(.text)
+	}
+
+	.bss ALIGN(4096) : {
+		_bss_start = .;
+		. = . + 4096;
+		_bss_end = .;
+	}
+
+	.stack ALIGN(4096) : {
+		. = . + 4096;
+		_stack_end = .;
+	}
+
+	.dtb ALIGN(4096) : {
 		dtb = .;
 		DTB_PATH
 	}
 
-	.kernel ALIGN(0x1000) : {
+	.kernel ALIGN(4096) : {
 		kernel = .;
 		KERNEL_PATH
 	}

arch/aarch64/macros.h

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2022, Ivaylo Ivanov <ivo.ivanov.ivanov1@gmail.com>
+ */
+
+.macro ENTRY name
+	.globl \name
+	.type \name, %function
+	.align 2
+	\name:
+.endm
+
+.macro ENDPROC name
+	.size \name, . - \name
+.endm

arch/aarch64/start.S

@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2022, Ivaylo Ivanov <ivo.ivanov.ivanov1@gmail.com>
+ */
+.include "arch/aarch64/macros.h"
+
+.section .text
+ENTRY _start
+	/* Set up the base address for the stack */
+	adr x0, _stack_end
+
+	/* Set up the stack pointer (SP) */
+	mov sp, x0
+
+	/* Fall through */
+	adr	x0, dtb
+	adr	x1, kernel
+	b main
+
+ENTRY load_kernel
+	br	x4
+ENDPROC load_kernel

arch/arm/linker.lds.S

@@ -14,7 +14,7 @@ SECTIONS
         . = __start_address;
 	
         .boot : {
-                arch/arm/Start.o
+                arch/arm/start.o
         }
 
         .dtb ALIGN(0x1000) : {