From 24ab4678b96dec56129f7e36b9304b6767777e0a Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Thu, 3 Oct 2019 14:04:31 +0200
Subject: specify load address only in linker script; change it to 0x10000 (for
 now); avoid padding

---
 Makefile  | 10 +++-------
 boot.S    |  8 +++++---
 linker.ld |  7 +++++--
 3 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/Makefile b/Makefile
index 2e2f062..8ad7c03 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 all : kernel7.img
 
 kernel.o : kernel.c
-	arm-none-eabi-gcc -mcpu=cortex-a7 -ffreestanding -std=gnu99 -c -O2 -Wall -Wextra $^ -o $@
+	arm-none-eabi-gcc -mcpu=cortex-a7 -ffreestanding -std=gnu99 -c -Wall -Wextra $^ -o $@
 
 boot.o : boot.S
 	arm-none-eabi-as -mcpu=cortex-a7 boot.S -o boot.o
@@ -9,13 +9,9 @@ boot.o : boot.S
 kernel.elf : boot.o kernel.o
 	arm-none-eabi-gcc -T linker.ld -o $@ -ffreestanding -O2 -nostdlib boot.o kernel.o -lgcc
 
-# objcopy pads 0x0000 to 0x8000 with zeros, we get rid of them in the next recipe
-kernel_padded.img : kernel.elf
+kernel7.img : kernel.elf
 	arm-none-eabi-objcopy $^ -O binary $@
 
-kernel7.img : kernel_padded.img
-	dd bs=4096 skip=8 if=$^ of=$@
-
 qemu-elf : kernel.elf
 	qemu-system-arm -m 256 -M raspi2 -serial stdio -kernel $^
 
@@ -23,6 +19,6 @@ qemu-bin : kernel7.img
 	qemu-system-arm -m 256 -M raspi2 -serial stdio -kernel $^
 
 clean :
-	-rm kernel7.img kernel_padded.img kernel.elf boot.o kernel.o
+	-rm kernel7.img kernel.elf boot.o kernel.o
 
 .PHONY: all qemu-elf qemu-bin clean
diff --git a/boot.S b/boot.S
index da8aca7..20cf155 100644
--- a/boot.S
+++ b/boot.S
@@ -2,11 +2,12 @@
  
 // To keep this in the first portion of the binary.
 .section ".text.boot"
- 
+
+//.org 0x8000
+	
 // Make _start global.
 .globl _start
  
-.org 0x8000
 // Entry point for the kernel.
 // r15 -> should begin execution at 0x8000.
 // r0 -> 0x00000000
@@ -21,7 +22,8 @@ _start:
         bne halt
  
         // Setup the stack.
-        ldr r5, =_start
+	// It shall be directly below our kernel image
+        ldr r5, =__start
         mov sp, r5
  
         // Clear out bss.
diff --git a/linker.ld b/linker.ld
index 7f3ee57..0cbd1fb 100644
--- a/linker.ld
+++ b/linker.ld
@@ -3,8 +3,11 @@ ENTRY(_start)
 SECTIONS
 {
     /* Starts at LOADER_ADDR. */
-    . = 0x8000;
-    /* For AArch64, use . = 0x80000; */
+    /* Warning! Internet says RPis in 32-bit mode load kernel at 0x8000! */
+    /* My experiments do, however, show, that qemu emulating RPi2 */
+    /* Loads the kernel at 0x10000! (took some pain to find out) */
+    . = 0x10000;
+    /* For AArch64, use . = 0x80000; Unless this too is wrong */
     __start = .;
     __text_start = .;
     .text :
-- 
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