aarch64: introduce early relocation of the bootloader

All newer exynos devices with s-boot have the "feature" of placing the
android kernel at a random location in dram, specifically around
0x80000000 and 0x83000000. This made it hard to assume where we are at,
hence why we made everything as PiE (position-independent) as possible.

This, however, resulted in a lot of issues. I usually managed to get
around them with ugly hacks, but in the last 5-6 commits, with the
fixed support for armv7, everything fell apart for arm64.

So, the solution for this is to implement code at the beginning
of the bootloader that relocates it to a safe place in memory.
This is currently enabled for dreamlte, and it must be enabled
and configured for all other boards with that issue. Otherwise they
will NOT boot anymore. Boards that don't need this can keep
CONFIG_POSITION_INDEPENDENT disabled.

Kconfig

@@ -4,6 +4,8 @@
 #
 mainmenu "uniLoader Configuration"
 
+source "arch/Kconfig"
+
 menu "Building options"
 	config CROSS_COMPILE
 		string "Cross-compiler tool prefix"

Makefile

@@ -373,7 +373,8 @@ all: arch/$(ARCH)/linker.lds uniLoader
 
 # Generate linker script from template
 quiet_cmd_cpp_lds = LDS     $@
-      cmd_cpp_lds = $(CPP) $< -DTEXT_BASE=$(TEXT_BASE) \
+      cmd_cpp_lds = $(CPP)  -include include/generated/autoconf.h $< \
+                            -DTEXT_BASE=$(TEXT_BASE) \
                             -DKERNEL_PATH=$(KERNEL_PATH) \
                             -DDTB_PATH=$(DT_PATH) \
                             -DRAMDISK_PATH=$(RAMDISK_PATH) \

arch/Kconfig

@@ -0,0 +1,7 @@
+menu "Architecture"
+	config POSITION_INDEPENDENT
+		bool "Code relocation during early boot"
+		help
+		  Say Y if your previous bootloader loads uniLoader at an unknown
+		  or different address every time.
+endmenu

arch/aarch64/Makefile

@@ -2,4 +2,5 @@
 #
 # Copyright (c) 2025 Ivaylo Ivanov <ivo.ivanov.ivanov1@gmail.com>
 
+obj-$(CONFIG_POSITION_INDEPENDENT) += aarch64/reloc.o
 obj-y += aarch64/start.o aarch64/memcpy.o

arch/aarch64/linker.lds.S

@@ -2,8 +2,14 @@
 /*
  * Copyright (c) 2022, Ivaylo Ivanov <ivo.ivanov.ivanov1@gmail.com>
  */
+ENTRY(
+#ifdef CONFIG_POSITION_INDEPENDENT
+      _head
+#else
+      _start
+#endif
+     );
 
-ENTRY(_start);
 
 OUTPUT_FORMAT("elf64-littleaarch64")
 OUTPUT_ARCH(aarch64)
@@ -15,12 +21,31 @@ INPUT(RAMDISK_PATH)
 
 SECTIONS
 {
+	. = TEXT_BASE;
+
 	.text : {
-		KEEP(*(.text.start))
+#ifdef CONFIG_POSITION_INDEPENDENT
+		_reloc_start = .;
+#endif
 		*(.text)
 		*(.text.*)
 	}
 
+	.kernel ALIGN(4096) : {
+		kernel = .;
+		KERNEL_PATH
+	}
+
+	.dtb ALIGN(4096) : {
+		dtb = .;
+		DTB_PATH
+	}
+
+	.ramdisk ALIGN(4096) : {
+		ramdisk = .;
+		RAMDISK_PATH
+	}
+
 	.rodata ALIGN(4) : {
 		*(.rodata)
 		*(.rodata.*)
@@ -42,23 +67,14 @@ SECTIONS
 	.stack ALIGN(4096) : {
 		. = . + 4096;
 		_stack_end = .;
-	}
-
-	.dtb ALIGN(4096) : {
-		dtb = .;
-		DTB_PATH
-	}
-
-	.kernel ALIGN(4096) : {
-		kernel = .;
-		KERNEL_PATH
-	}
-
-	.ramdisk ALIGN(4096) : {
-		ramdisk = .;
-		RAMDISK_PATH
+#ifdef CONFIG_POSITION_INDEPENDENT
+		_reloc_end = .;
+#endif
 	}
 
 	kernel_size = SIZEOF(.kernel);
 	ramdisk_size = SIZEOF(.ramdisk);
+#ifdef CONFIG_POSITION_INDEPENDENT
+	_reloc_size = _reloc_end - _reloc_start;
+#endif
 }

arch/aarch64/reloc.S

@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2025, Ivaylo Ivanov <ivo.ivanov.ivanov1@gmail.com>
+ */
+#include "asmdefs.h"
+
+.extern _reloc_size
+.extern _start
+
+ENTRY_ALIAS(_head)
+	adr	x1, _relocated_uni
+	b	 _reloc_entry
+
+ENTRY_ALIAS(_rel_stack_base)
+	.quad _start
+
+ENTRY_ALIAS(_rel_stack_size)
+	.quad _reloc_size
+	.quad 0
+	.quad 0
+	.quad 0
+	.quad 0
+	.ascii "ARM\x64"
+	.long 0
+
+ENTRY_ALIAS( _reloc_entry)
+	adr	x4, _start
+	ldr	x5, _rel_stack_base
+	cmp	x4, x5
+	beq	_entry
+	ldr	x6,  _rel_stack_size
+
+_copy:
+	ldp	x2, x3, [x4], #16
+	stp	x2, x3, [x5], #16
+	subs	x6, x6, #16
+	b.ne	_copy
+	ldr	x5, _rel_stack_base
+
+_entry:
+	br	x5
+
+_dead: /* we should never get here */
+	b	_dead
+
+ENTRY_ALIAS(_relocated_uni)

arch/aarch64/start.S

@@ -27,3 +27,4 @@ END(_start)
 ENTRY(load_kernel_and_jump)
 	br	x4
 END(load_kernel_and_jump)
+

configs/dreamlte_defconfig

@@ -1,7 +1,9 @@
+CONFIG_POSITION_INDEPENDENT=y
 CONFIG_EXYNOS_8895=y
 CONFIG_SAMSUNG_DREAMLTE=y
+CONFIG_TEXT_BASE=0x87000000
 CONFIG_PAYLOAD_ENTRY=0x90000000
-CONFIG_RAMDISK_ENTRY=0x82000000
+CONFIG_RAMDISK_ENTRY=0x84000000
 CONFIG_FRAMEBUFFER_BASE=0xcc000000
 CONFIG_FRAMEBUFFER_WIDTH=1440
 CONFIG_FRAMEBUFFER_HEIGHT=2960

main/main.c

@@ -44,7 +44,6 @@ void main(void* dt, void* kernel, void* ramdisk)
 
 	/* Copy kernel to memory and boot  */
 	printk(-1, "booting linux...\n");
-
 #ifdef __aarch64__
 	memcpy((void*)CONFIG_PAYLOAD_ENTRY, kernel, (unsigned long) &kernel_size);
 	__optimized_memcpy((void*)CONFIG_RAMDISK_ENTRY, ramdisk, (unsigned long) &ramdisk_size);