From 4c110d2802742fe1d37ba7280f374174fc45cbe1 Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Tue, 24 Dec 2019 22:43:07 +0100
Subject: simplify linking of libkernel

---
 linker.ld | 63 ++++++++++++++++++---------------------------------------------
 1 file changed, 18 insertions(+), 45 deletions(-)

(limited to 'linker.ld')

diff --git a/linker.ld b/linker.ld
index 01eda35..387e7c7 100644
--- a/linker.ld
+++ b/linker.ld
@@ -1,18 +1,21 @@
-ENTRY(_start)
+ENTRY(_start) /* defined in boot.S */
  
 SECTIONS
 {
-    /* Starts at LOADER_ADDR, which is 0x8000 - that's where RPis in */
-    /* 32-bit mode load kernel at. */
+    /* Starts at  0x8000 - that's where RPis in 32-bit mode load kernel at. */
     /* My experiments do, however, show, that qemu emulating RPi2 */
     /* loads the kernel at 0x10000! (took some pain to find out). */
-    /* Since we're using a bootloader now, we can compile the kernel */
-    /* for 0x8000 and bootloader will load it properly (although it */
-    /* itself still has to be compiled for 0x10000) */
-    /* rpi-open-firmware, ont he other hand, loads kernel at 0x2000000 */
-    /* This issue is also to be avoided by the use of bootloader */
+    /* rpi-open-firmware, on the other hand, loads kernel at 0x2000000! */
+    /* This is not really a problem, since: */
+    /*   1. We can use out bootloader to load the kernel at 0x8000 */
+    /*   2. We compile kernel with -fPIC, so it should be able to work with */
+    /*      any load addr.
+    /*   3. In qemu, we can load kernel.elf instead of raw binary */
+    /*      (qemu will do the loading then) */
+
     . = 0x8000;
-    /* For AArch64, use . = 0x80000; Unless this too is wrong in qemu… */
+
+    /* For AArch64, use . = 0x80000 */
     
     __start = .;
     __text_start = .;
@@ -51,44 +54,14 @@ SECTIONS
     __bss_size = __bss_end - __bss_start;
 
 
-
-    /* Here come the definitions for renamed sections */
-    __renamed_start = .;
-    __renamed_text_start = .;
-    .renamed_text :
-    {
-        *(.renamed_text)
-    }
-    . = ALIGN(4096); /* align to page size */
-    __renamed_text_end = .;
- 
-    __renamed_rodata_start = .;
-    .renamed_rodata :
-    {
-        *(.renamed_rodata)
-    }
-    . = ALIGN(4096); /* align to page size */
-    __renamed_rodata_end = .;
- 
-    __renamed_data_start = .;
-    .renamed_data :
-    {
-        *(.renamed_data)
-    }
-    . = ALIGN(4096); /* align to page size */
-    __renamed_data_end = .;
- 
-    __renamed_bss_start = .;
-    .renamed_bss :
+    /* libkernel */
+    .libkernel :
     {
-        renamed_bss = .;
-        *(.renamed_bss)
+	__libkernel_start = .;
+	libkernel.o
+	__libkernel_end = .;
     }
-    . = ALIGN(4096); /* align to page size */
-    __renamed_bss_end = .;
-    __renamed_bss_size = __renamed_bss_end - __renamed_bss_start;
-    __renamed_end = .;
-    __renamed_size = __renamed_end - __renamed_start;
+    __libkernel_size = __libkernel_end - __libkernel_start;
 
 
     . = ALIGN(4096); /* align to page size */
-- 
cgit v1.2.3


From 6a5684927d5a6d201b407ff30340307fe9813677 Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Thu, 26 Dec 2019 17:55:15 +0100
Subject: fix linking of libkernel

---
 linker.ld | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

(limited to 'linker.ld')

diff --git a/linker.ld b/linker.ld
index 387e7c7..60387bf 100644
--- a/linker.ld
+++ b/linker.ld
@@ -22,7 +22,7 @@ SECTIONS
     .text :
     {
         KEEP(*(.text.boot))
-        *(.text)
+	*(EXCLUDE_FILE (libkernel.o) .text)
     }
     . = ALIGN(4096); /* align to page size */
     __text_end = .;
@@ -30,7 +30,7 @@ SECTIONS
     __rodata_start = .;
     .rodata :
     {
-        *(.rodata)
+        *(EXCLUDE_FILE (libkernel.o) .rodata)
     }
     . = ALIGN(4096); /* align to page size */
     __rodata_end = .;
@@ -38,7 +38,7 @@ SECTIONS
     __data_start = .;
     .data :
     {
-        *(.data)
+        *(EXCLUDE_FILE (libkernel.o) .data)
     }
     . = ALIGN(4096); /* align to page size */
     __data_end = .;
@@ -47,7 +47,7 @@ SECTIONS
     .bss :
     {
         bss = .;
-        *(.bss)
+        *(EXCLUDE_FILE (libkernel.o) .bss)
     }
     . = ALIGN(4096); /* align to page size */
     __bss_end = .;
-- 
cgit v1.2.3


From 93a1c704c99a48803d118f66ac4fe08510fb4b89 Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Thu, 26 Dec 2019 18:21:29 +0100
Subject: simplify linker script; rely on initially-zero memory to be included
 in binary image (no bss zeroing in assembly code)

---
 boot.S    | 20 +-------------------
 linker.ld | 36 +++++++-----------------------------
 2 files changed, 8 insertions(+), 48 deletions(-)

(limited to 'linker.ld')

diff --git a/boot.S b/boot.S
index 5e510f8..a792c94 100644
--- a/boot.S
+++ b/boot.S
@@ -1,7 +1,7 @@
 // armv7 mode
  
 // To keep this in the first portion of the binary.
-.section ".text.boot"
+.section ".boot"
 
 //.org 0x8000
 	
@@ -30,24 +30,6 @@ _start:
         ldr r5, =__start
         mov sp, r5
  
-        // Clear out bss.
-        ldr r4, =__bss_start
-        ldr r9, =__bss_end
-        mov r5, #0
-        mov r6, #0
-        mov r7, #0
-        mov r8, #0
-        b       2f
- 
-1:
-        // store multiple at r4.
-        stmia r4!, {r5-r8}
- 
-        // If we are still below bss_end, loop.
-2:
-        cmp r4, r9
-        blo 1b
- 
         // Call kernel_main
         ldr r3, =kernel_main
         bx r3
diff --git a/linker.ld b/linker.ld
index 60387bf..ed40054 100644
--- a/linker.ld
+++ b/linker.ld
@@ -18,40 +18,18 @@ SECTIONS
     /* For AArch64, use . = 0x80000 */
     
     __start = .;
-    __text_start = .;
-    .text :
+    .boot :
     {
-        KEEP(*(.text.boot))
-	*(EXCLUDE_FILE (libkernel.o) .text)
+	boot.o
     }
-    . = ALIGN(4096); /* align to page size */
-    __text_end = .;
- 
-    __rodata_start = .;
-    .rodata :
-    {
-        *(EXCLUDE_FILE (libkernel.o) .rodata)
-    }
-    . = ALIGN(4096); /* align to page size */
-    __rodata_end = .;
- 
-    __data_start = .;
-    .data :
-    {
-        *(EXCLUDE_FILE (libkernel.o) .data)
-    }
-    . = ALIGN(4096); /* align to page size */
-    __data_end = .;
- 
-    __bss_start = .;
-    .bss :
+    __kernel_start = .;
+    .kernel :
     {
-        bss = .;
-        *(EXCLUDE_FILE (libkernel.o) .bss)
+	*(EXCLUDE_FILE (libkernel.o interrupt_vector.o interrupts.o) *)
     }
     . = ALIGN(4096); /* align to page size */
-    __bss_end = .;
-    __bss_size = __bss_end - __bss_start;
+    __kernel_end = .;
+    __kernel_size = __kernel_end - __kernel_start;
 
 
     /* libkernel */
-- 
cgit v1.2.3


From 9d587f9f750253461314757f2f861c5214563120 Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Thu, 26 Dec 2019 18:48:38 +0100
Subject: improve linking of interrupts

---
 demo_functionality.c | 10 +++++-----
 interrupt_vector.S   |  4 +++-
 interrupts.c         |  9 ++++++---
 linker.ld            | 18 +++++++++---------
 4 files changed, 23 insertions(+), 18 deletions(-)

(limited to 'linker.ld')

diff --git a/demo_functionality.c b/demo_functionality.c
index aedab08..c6f7e5c 100644
--- a/demo_functionality.c
+++ b/demo_functionality.c
@@ -164,9 +164,9 @@ void demo_go_unprivileged(void)
 }
 
 extern char
-  __interrupt_vectors_start,
-  __interrupt_vectors_end,
-  __interrupt_vectors_size;
+  __interrupts_start,
+  __interrupts_end,
+  __interrupts_size;
 
 extern void (*volatile system_reentry_point)(void);
 
@@ -180,7 +180,7 @@ void demo_setup_interrupts(void)
 {
   system_reentry_point = system_reentry;
 
-  for (size_t i = 0; i < (size_t) &__interrupt_vectors_size; i++)
+  for (size_t i = 0; i < (size_t) &__interrupts_size; i++)
     ((volatile char*) 0)[i] =
-      (&__interrupt_vectors_start)[i];
+      (&__interrupts_start)[i];
 }
diff --git a/interrupt_vector.S b/interrupt_vector.S
index f71330b..d20bf6d 100644
--- a/interrupt_vector.S
+++ b/interrupt_vector.S
@@ -1,4 +1,4 @@
-.section ".interrupt_vectors.text"
+.section ".interrupts.vector"
 
 .global abort_handler
 .local generic_handler	
@@ -12,6 +12,8 @@ _interrupt_vectors:
 	b generic_handler
 	b generic_handler
 
+.section ".interrupts.text"
+
 generic_handler:
 	b generic_handler
 abort_handler_caller:
diff --git a/interrupts.c b/interrupts.c
index 191ce40..6952f89 100644
--- a/interrupts.c
+++ b/interrupts.c
@@ -5,7 +5,10 @@
     If an undefined instruction is encountered, the CPU will start
     executing this function. Just trap here as a debug solution.
 */
-void __attribute__((interrupt("UNDEF"))) undefined_instruction_vector(void)
+void
+__attribute__((interrupt("UNDEF")))
+__attribute__((section(".interrupts.text")))
+undefined_instruction_vector(void)
 {
     uart_puts("Undefined instruction occured");
     while( 1 )
@@ -14,12 +17,12 @@ void __attribute__((interrupt("UNDEF"))) undefined_instruction_vector(void)
     }
 }
 
-void __attribute__((section(".interrupt_vectors.data")))
+void __attribute__((section(".interrupts.data")))
 (*system_reentry_point) (void);
 
 void
 __attribute__((interrupt("ABORT")))
-__attribute__((section(".interrupt_vectors.text")))
+__attribute__((section(".interrupts.text")))
 abort_handler(void)
 {
   system_reentry_point();
diff --git a/linker.ld b/linker.ld
index ed40054..5bdbfd2 100644
--- a/linker.ld
+++ b/linker.ld
@@ -42,17 +42,17 @@ SECTIONS
     __libkernel_size = __libkernel_end - __libkernel_start;
 
 
-    . = ALIGN(4096); /* align to page size */
-    __interrupt_vectors_start = .;
-    .interrupt_vectors :
+
+    .interrupts :
     {
-	interrupt_vectors = .;
-	*(.interrupt_vectors.text)
-	*(.interrupt_vectors.data)
+	__interrupts_start = .;
+	KEEP(*(.interrupts.vector))
+	interrupt_vector.o
+	interrupts.o
+    	__interrupts_end = .;
     }
-    . = ALIGN(4096); /* align to page size */
-    __interrupt_vectors_end = .;
-    __interrupt_vectors_size = __interrupt_vectors_end - __interrupt_vectors_start;
+    
+    __interrupts_size = __interrupts_end - __interrupts_start;
     
     __end = .;
 }
-- 
cgit v1.2.3


From 4d3cd9bd400b3d07d752d60ce2b3c425a53b72d6 Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Thu, 26 Dec 2019 19:02:32 +0100
Subject: improve linking of initial boot code

---
 boot.S    | 12 +++---------
 linker.ld | 14 +++++---------
 2 files changed, 8 insertions(+), 18 deletions(-)

(limited to 'linker.ld')

diff --git a/boot.S b/boot.S
index a792c94..ae56387 100644
--- a/boot.S
+++ b/boot.S
@@ -1,20 +1,14 @@
 // armv7 mode
  
-// To keep this in the first portion of the binary.
-.section ".boot"
-
-//.org 0x8000
-	
-// Make _start global.
-.globl _start
- 
 // Entry point for the kernel.
 // r15 -> should begin execution at 0x8000.
 // r0 -> 0x00000000
 // r1 -> 0x00000C42
 // r2 -> 0x00000100 - start of ATAGS
 // preserve these registers as argument for kernel_main
-_start:
+	
+.globl _boot // make entry point label global
+_boot:
         // Shut off extra cores
         mrc p15, 0, r5, c0, c0, 5
         and r5, r5, #3
diff --git a/linker.ld b/linker.ld
index 5bdbfd2..a0ad1ae 100644
--- a/linker.ld
+++ b/linker.ld
@@ -1,4 +1,4 @@
-ENTRY(_start) /* defined in boot.S */
+ENTRY(_boot) /* defined in boot.S; qemu needs it to run elf file */
  
 SECTIONS
 {
@@ -15,20 +15,16 @@ SECTIONS
 
     . = 0x8000;
 
-    /* For AArch64, use . = 0x80000 */
+    /* RPi in 64-bit mode uses address 0x80000 instead */
     
     __start = .;
-    .boot :
-    {
-	boot.o
-    }
-    __kernel_start = .;
     .kernel :
     {
+        __kernel_start = .;
+	KEEP(boot.o)
 	*(EXCLUDE_FILE (libkernel.o interrupt_vector.o interrupts.o) *)
+	__kernel_end = .;
     }
-    . = ALIGN(4096); /* align to page size */
-    __kernel_end = .;
     __kernel_size = __kernel_end - __kernel_start;
 
 
-- 
cgit v1.2.3


From d9ac897bd8aa7a8b6471bca1eb8a2bd314fdb133 Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Thu, 26 Dec 2019 19:06:18 +0100
Subject: minor changes (comments, whitespace)

---
 linker.ld | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

(limited to 'linker.ld')

diff --git a/linker.ld b/linker.ld
index a0ad1ae..33ac68c 100644
--- a/linker.ld
+++ b/linker.ld
@@ -2,16 +2,17 @@ ENTRY(_boot) /* defined in boot.S; qemu needs it to run elf file */
  
 SECTIONS
 {
-    /* Starts at  0x8000 - that's where RPis in 32-bit mode load kernel at. */
-    /* My experiments do, however, show, that qemu emulating RPi2 */
-    /* loads the kernel at 0x10000! (took some pain to find out). */
-    /* rpi-open-firmware, on the other hand, loads kernel at 0x2000000! */
+    /* Starts at  0x8000 - that's where RPis in 32-bit mode load */
+    /* kernel at. My experiments do, however, show, that qemu */
+    /* emulating RPi2 loads the kernel at 0x10000! (took some pain */
+    /* to find out). rpi-open-firmware, on the other hand, loads */
+    /* kernel at 0x2000000! */
     /* This is not really a problem, since: */
-    /*   1. We can use out bootloader to load the kernel at 0x8000 */
-    /*   2. We compile kernel with -fPIC, so it should be able to work with */
-    /*      any load addr.
+    /*   1. We can use our bootloader to load the kernel at 0x8000 */
+    /*   2. We compile kernel with -fPIC, so it should be able to */
+    /*      work with any load addr. */
     /*   3. In qemu, we can load kernel.elf instead of raw binary */
-    /*      (qemu will do the loading then) */
+    /*      (qemu will do the right thing then) */
 
     . = 0x8000;
 
@@ -38,7 +39,6 @@ SECTIONS
     __libkernel_size = __libkernel_end - __libkernel_start;
 
 
-
     .interrupts :
     {
 	__interrupts_start = .;
@@ -47,7 +47,6 @@ SECTIONS
 	interrupts.o
     	__interrupts_end = .;
     }
-    
     __interrupts_size = __interrupts_end - __interrupts_start;
     
     __end = .;
-- 
cgit v1.2.3


From 19efd77944dd42c3451a19e60a6948a52bc9ccad Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Thu, 26 Dec 2019 19:22:24 +0100
Subject: minor changes to boot code

---
 boot.S    | 18 ++++++++----------
 linker.ld |  2 ++
 2 files changed, 10 insertions(+), 10 deletions(-)

(limited to 'linker.ld')

diff --git a/boot.S b/boot.S
index be858ee..0cd0339 100644
--- a/boot.S
+++ b/boot.S
@@ -7,26 +7,24 @@
 // r2 -> 0x00000100 - start of ATAGS
 // preserve these registers as argument for kernel_main
 	
-.globl _boot // make entry point label global
+.global _boot // make entry point label global
 _boot:
-        // Shut off extra cores
-        mrc p15, 0, r5, c0, c0, 5
-        and r5, r5, #3
-        cmp r5, #0
+        // Only let the first core execute
+        mrc p15, 0, r3, c0, c0, 5
+        and r3, r3, #3
+        cmp r3, #0
         beq proceed
 	// this is a kind of blef - races can theoretically still occur
 	// when the main core overwrites this part of memory
 	wfe
 
 proceed:
-	// go to system mode
+	// go to system mode (we had problems doing this later)
 	cps #0b11111
 	isb
 	
-        // Setup the stack.
-	// It shall be directly below our kernel image
-        ldr r5, =__start
-        mov sp, r5
+        // Initialize the stack (_stack_top is defined in linker.ld)
+        ldr sp, =_stack_top
  
         // Call kernel_main
         ldr r3, =kernel_main
diff --git a/linker.ld b/linker.ld
index 33ac68c..e0e72b2 100644
--- a/linker.ld
+++ b/linker.ld
@@ -50,4 +50,6 @@ SECTIONS
     __interrupts_size = __interrupts_end - __interrupts_start;
     
     __end = .;
+
+    _stack_top = __start;
 }
-- 
cgit v1.2.3


From 826d5b3ba04a8b830c8a92a6f69ca4e223257c5b Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Sat, 28 Dec 2019 14:01:14 +0100
Subject: place PL_0_test.img in ramfs instead of embedding it directly

---
 Makefile             |  7 ++++++-
 demo_functionality.c | 21 ++++++++++++++++-----
 linker.ld            |  4 +++-
 3 files changed, 25 insertions(+), 7 deletions(-)

(limited to 'linker.ld')

diff --git a/Makefile b/Makefile
index 3d6b095..b8800cc 100644
--- a/Makefile
+++ b/Makefile
@@ -5,6 +5,8 @@ ARM_OBJECTS=kernel.o paging.o demo_functionality.o PL0_test.o uart.o loader_stag
 
 EMBEDDABLE_OBJECTS=PL_0_test_embeddable.o loader_stage2_embeddable.o
 
+RAMFS_FILES=PL_0_test.img
+
 all : kernel7.img
 
 %.o : %.c
@@ -22,7 +24,7 @@ all : kernel7.img
 PL_0_test.elf : PL0_test.o uart.o
 	arm-none-eabi-gcc -T PL0_test.ld -o $@ $(ELFFLAGS) $^
 
-kernel.elf : boot.o kernel.o uart.o PL_0_test_embeddable.o demo_functionality.o paging.o libkernel.o interrupt_vector.o interrupts.o
+kernel.elf : boot.o kernel.o uart.o demo_functionality.o paging.o libkernel.o interrupt_vector.o interrupts.o ramfs_embeddable.o ramfs.o
 	arm-none-eabi-gcc -T linker.ld -o $@ $(ELFFLAGS) $^
 
 loader.elf : boot.o loader_stage1.o loader_stage2.o uart.o
@@ -49,6 +51,9 @@ pipe_image : pipe_image.c lib/rs232/rs232.c
 makefs : makefs.c
 	gcc -Wall -std=gnu99 -O3 $^ -o $@
 
+ramfs.img : makefs $(RAMFS_FILES)
+	./makefs $(RAMFS_FILES) > $@
+
 clean :
 	-rm *.img *.elf *.o pipe_image
 
diff --git a/demo_functionality.c b/demo_functionality.c
index c6f7e5c..206dd2b 100644
--- a/demo_functionality.c
+++ b/demo_functionality.c
@@ -3,6 +3,7 @@
 #include "memory.h"
 #include "translation_table_descriptors.h"
 #include "libkernel.h"
+#include "ramfs.h"
 
 void demo_paging_support(void)
 {
@@ -88,12 +89,22 @@ void demo_setup_libkernel(void) {
 }
 
 extern char
-  _binary_PL_0_test_img_start,
-  _binary_PL_0_test_img_end,
-  _binary_PL_0_test_img_size;
+  _binary_ramfs_img_start,
+  _binary_ramfs_img_end,
+  _binary_ramfs_img_size;
 
 void demo_setup_PL0(void)
 {
+  // find PL_0_test.img im ramfs
+  struct ramfile PL_0_test_img;
+
+  if (find_file(&_binary_ramfs_img_start, "PL_0_test.img",
+		&PL_0_test_img))
+    {
+      uart_puts("PL_0_test.img not found :(\r\n");
+      asm volatile ("wfi");
+    }
+
   short_section_descriptor_t volatile *PL0_section_entry =
     &TRANSLATION_TABLE[PL0_SECTION_NUMBER];
   short_section_descriptor_t volatile *UART_memory_section_entry =
@@ -136,9 +147,9 @@ void demo_setup_PL0(void)
   uart_puts((char*) VIRTUAL_PL0_MEMORY_START);
 
   // now paste a userspace program to that section
-  for (size_t i = 0; i < (size_t) &_binary_PL_0_test_img_size; i++)
+  for (uint32_t i = 0; i < PL_0_test_img.file_size; i++)
     ((volatile char*) VIRTUAL_PL0_MEMORY_START)[i] =
-      (&_binary_PL_0_test_img_start)[i];
+      PL_0_test_img.file_contents[i];
 
   uart_puts("copied PL0 and libkernel code to their sections\n\r");
 }
diff --git a/linker.ld b/linker.ld
index e0e72b2..7b585dc 100644
--- a/linker.ld
+++ b/linker.ld
@@ -23,7 +23,9 @@ SECTIONS
     {
         __kernel_start = .;
 	KEEP(boot.o)
-	*(EXCLUDE_FILE (libkernel.o interrupt_vector.o interrupts.o) *)
+	*(EXCLUDE_FILE (ramfs_embeddable.o libkernel.o interrupt_vector.o interrupts.o) *)
+	. = ALIGN(4);
+	ramfs_embeddable.o
 	__kernel_end = .;
     }
     __kernel_size = __kernel_end - __kernel_start;
-- 
cgit v1.2.3


From c374eaacbc0d16983bbd1112fefa74dbe88e1e53 Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Sat, 28 Dec 2019 15:55:29 +0100
Subject: use ldm instruction instead of libkernel for entering user mode; get
 rid of libkernel (no longer needed)

---
 Makefile             |  2 +-
 demo_functionality.c | 69 +++++++++++++++++-----------------------------------
 kernel.c             |  2 --
 libkernel.c          | 12 ---------
 libkernel.h          |  6 -----
 linker.ld            | 11 ---------
 memory.h             | 13 ++--------
 psr.h                | 15 ++++++++++++
 8 files changed, 40 insertions(+), 90 deletions(-)
 delete mode 100644 libkernel.c
 delete mode 100644 libkernel.h

(limited to 'linker.ld')

diff --git a/Makefile b/Makefile
index b8800cc..55d0d1b 100644
--- a/Makefile
+++ b/Makefile
@@ -24,7 +24,7 @@ all : kernel7.img
 PL_0_test.elf : PL0_test.o uart.o
 	arm-none-eabi-gcc -T PL0_test.ld -o $@ $(ELFFLAGS) $^
 
-kernel.elf : boot.o kernel.o uart.o demo_functionality.o paging.o libkernel.o interrupt_vector.o interrupts.o ramfs_embeddable.o ramfs.o
+kernel.elf : boot.o kernel.o uart.o demo_functionality.o paging.o interrupt_vector.o interrupts.o ramfs_embeddable.o ramfs.o
 	arm-none-eabi-gcc -T linker.ld -o $@ $(ELFFLAGS) $^
 
 loader.elf : boot.o loader_stage1.o loader_stage2.o uart.o
diff --git a/demo_functionality.c b/demo_functionality.c
index 206dd2b..4b002d6 100644
--- a/demo_functionality.c
+++ b/demo_functionality.c
@@ -2,7 +2,6 @@
 #include "psr.h"
 #include "memory.h"
 #include "translation_table_descriptors.h"
-#include "libkernel.h"
 #include "ramfs.h"
 
 void demo_paging_support(void)
@@ -57,37 +56,6 @@ void demo_current_mode(void)
 #define TRANSLATION_TABLE						\
   ((short_section_descriptor_t volatile*) TRANSLATION_TABLE_BASE)
 
-extern char
-  __libkernel_start,
-  __libkernel_end,
-  __libkernel_size;
-
-void demo_setup_libkernel(void) {
-  short_section_descriptor_t volatile *libkernel_section_entry =
-    &TRANSLATION_TABLE[LIBKERNEL_SECTION_NUMBER];
-
-  short_section_descriptor_t
-    libkernel_section = *libkernel_section_entry;
-
-  // make libkernel section executable and read-only for
-  // unprivileged code
-  libkernel_section.ACCESS_PERMISSIONS_2 =
-    AP_2_0_MODEL_RW_PL1_RO_PL0 >> 2;
-  libkernel_section.ACCESS_PERMISSIONS_1_0 =
-    AP_2_0_MODEL_RW_PL1_RO_PL0 & 0b011;
-
-  *libkernel_section_entry = libkernel_section;  
-
-  // invalidate main Translation Lookup Buffer (just in case)
-  asm("mcr p15, 0, %0, c8, c7, 0\n\r"
-      "isb" :: "r" (0) : "memory");
-  
-  // copy libkernel code to libkernel section
-  for (size_t i = 0; i < (size_t) &__libkernel_size; i++)
-    ((volatile char*) LIBKERNEL_SECTION_START)[i] =
-      (&__libkernel_start)[i];
-}
-
 extern char
   _binary_ramfs_img_start,
   _binary_ramfs_img_end,
@@ -151,27 +119,34 @@ void demo_setup_PL0(void)
     ((volatile char*) VIRTUAL_PL0_MEMORY_START)[i] =
       PL_0_test_img.file_contents[i];
 
-  uart_puts("copied PL0 and libkernel code to their sections\n\r");
+  uart_puts("copied PL0 code to it's section\n\r");
+}
+
+// needed for array initialization in demo_go_unprivileged()
+void *memset(void *s, int c, size_t n)
+{
+  char *mem = s;
+  
+  for (size_t i = 0; i < n; i++)
+    mem[i] = c;
+  
+  return s;
 }
 
 void demo_go_unprivileged(void)
 {
-  size_t call_unprivileged_offset =
-    (size_t) &call_unprivileged - (size_t) &__libkernel_start;
+  uint32_t PL0_regs[16] = {0};
+  PL0_regs[15] = VIRTUAL_PL0_MEMORY_START;       // the new pc
+  PL0_regs[13] = (PL0_SECTION_NUMBER + 1) << 20; // the new sp
+
+  PSR_t new_SPSR = read_CPSR();
+  new_SPSR.fields.PSR_MODE_4_0 = MODE_USER;
+  write_SPSR(new_SPSR);
 
-  void *call_unprivileged_new_location =
-    (void*) (LIBKERNEL_SECTION_START + call_unprivileged_offset);
+  uart_puts("All ready, jumping to PL0 code\n\r");
   
-  // call call_unprivileged from libkernel
-  asm volatile("mov  r5, %0\n\r"
-	       "mov  r0, %1\n\r"
-	       "mov  r4, #0\n\r"
-  	       "movt r4, #"PL0_SECTION_NUMBER_STR"1111\n\r"
-  	       "mov  sp, r4\n\r" // setting stack is important :D
-  	       "blx  r5\n\r" ::
-	       "r" (call_unprivileged_new_location),
-	       "r" (VIRTUAL_PL0_MEMORY_START)
-	       : "memory", "r4", "r5", "r0");
+  asm volatile("ldm %0, {r0 - r15} ^" ::
+	       "r" (PL0_regs));
 }
 
 extern char
diff --git a/kernel.c b/kernel.c
index fc629e1..9cdb82a 100644
--- a/kernel.c
+++ b/kernel.c
@@ -27,8 +27,6 @@ void kernel_main(uint32_t r0, uint32_t r1, uint32_t atags)
   // prints some info and sets upp translation table, turns on MMU
   setup_flat_map();
 
-  demo_setup_libkernel();
-
   demo_setup_PL0();
 
   demo_setup_interrupts();
diff --git a/libkernel.c b/libkernel.c
deleted file mode 100644
index 0955e0e..0000000
--- a/libkernel.c
+++ /dev/null
@@ -1,12 +0,0 @@
-// This is the privileged code, that gets placed somewhere in
-// unprivileged process' address space. It's compiled as relocatable,
-// so it can be loaded at different address for different processes.
-
-void call_unprivileged(void (*address) (void)) {
-  // switch to PL0
-  asm("cps #0b10000\n\r"
-      "isb" ::: "memory");
-
-  // jump to that unprivileged code
-  address();
-}
diff --git a/libkernel.h b/libkernel.h
deleted file mode 100644
index a8af348..0000000
--- a/libkernel.h
+++ /dev/null
@@ -1,6 +0,0 @@
-#ifndef LIBKERNEL_H
-#define LIBKERNEL_H
-
-void call_unprivileged(void (*address) (void));
-
-#endif // LIBKERNEL_H
diff --git a/linker.ld b/linker.ld
index 7b585dc..673d7e2 100644
--- a/linker.ld
+++ b/linker.ld
@@ -30,17 +30,6 @@ SECTIONS
     }
     __kernel_size = __kernel_end - __kernel_start;
 
-
-    /* libkernel */
-    .libkernel :
-    {
-	__libkernel_start = .;
-	libkernel.o
-	__libkernel_end = .;
-    }
-    __libkernel_size = __libkernel_end - __libkernel_start;
-
-
     .interrupts :
     {
 	__interrupts_start = .;
diff --git a/memory.h b/memory.h
index 1c9ae35..d369694 100644
--- a/memory.h
+++ b/memory.h
@@ -24,24 +24,15 @@ extern const char __start;
 #define TRANSLATION_TABLE_END				\
   (TRANSLATION_TABLE_BASE + (uint32_t) (4096 * 4))
 
-#define LIBKERNEL_SECTION_START					\
-  (((TRANSLATION_TABLE_END - (uint32_t) 1) & ~((uint32_t) 0xfffff))	\
+#define PRIVILEGED_MEMORY_END					     \
+  (((TRANSLATION_TABLE_END - (uint32_t) 1) & ~((uint32_t) 0xfffff))  \
    + SECTION_SIZE)
 
-#define LIBKERNEL_SECTION_END			\
-  (LIBKERNEL_SECTION_START + SECTION_SIZE)
-
-// section for libkernel is flat-mapped
-#define LIBKERNEL_SECTION_NUMBER (LIBKERNEL_SECTION_START >> 20)
-
-#define PRIVILEGED_MEMORY_END LIBKERNEL_SECTION_END
-
 #define UNPRIVILEGED_MEMORY_START PRIVILEGED_MEMORY_END
 #define UNPRIVILEGED_MEMORY_END			\
   (UNPRIVILEGED_MEMORY_START + SECTION_SIZE)
 
 #define PL0_SECTION_NUMBER     ((uint32_t) 0b101010101010)
-#define PL0_SECTION_NUMBER_STR "0b101010101010"
 
 #define VIRTUAL_PL0_MEMORY_START (PL0_SECTION_NUMBER << 20)
 
diff --git a/psr.h b/psr.h
index 9809fc4..b2adafb 100644
--- a/psr.h
+++ b/psr.h
@@ -64,4 +64,19 @@ inline static PSR_t read_CPSR(void)
   return CPSR;
 }
 
+inline static PSR_t read_SPSR(void)
+{
+  PSR_t SPSR;
+  // get content of saved program status register
+  asm("mrs %0, spsr" : "=r" (SPSR.raw) :: "memory");
+  
+  return SPSR;
+}
+
+inline static void write_SPSR(PSR_t SPSR)
+{
+  // set content of saved program status register
+  asm("msr spsr, %0" :: "r" (SPSR.raw));
+}
+
 #endif // PSR_H
-- 
cgit v1.2.3


From 38afee0bfe051f1c1e5b9426395eb50b9d8a7bc2 Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Sat, 28 Dec 2019 18:53:16 +0100
Subject: correct the notion of PIC in the comment

---
 linker.ld | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

(limited to 'linker.ld')

diff --git a/linker.ld b/linker.ld
index 673d7e2..444bbf6 100644
--- a/linker.ld
+++ b/linker.ld
@@ -9,8 +9,9 @@ SECTIONS
     /* kernel at 0x2000000! */
     /* This is not really a problem, since: */
     /*   1. We can use our bootloader to load the kernel at 0x8000 */
-    /*   2. We compile kernel with -fPIC, so it should be able to */
-    /*      work with any load addr. */
+    /*   2. Stage 1 of the bootloader is written in careful */
+    /*      assembly, so that the loader itself should work */
+    /*      regardless of where it is loaded. */
     /*   3. In qemu, we can load kernel.elf instead of raw binary */
     /*      (qemu will do the right thing then) */
 
@@ -23,9 +24,9 @@ SECTIONS
     {
         __kernel_start = .;
 	KEEP(boot.o)
-	*(EXCLUDE_FILE (ramfs_embeddable.o libkernel.o interrupt_vector.o interrupts.o) *)
 	. = ALIGN(4);
 	ramfs_embeddable.o
+	*(EXCLUDE_FILE (libkernel.o interrupt_vector.o interrupts.o) *)
 	__kernel_end = .;
     }
     __kernel_size = __kernel_end - __kernel_start;
-- 
cgit v1.2.3


From 700f4c412d42c9b9811269045c0e363a0331bba9 Mon Sep 17 00:00:00 2001
From: Wojtek Kosior <kwojtus@protonmail.com>
Date: Sat, 28 Dec 2019 21:54:42 +0100
Subject: split kernel into 2 stages; second stage gets copied to 0x0 and runs
 from there

---
 Makefile             | 29 ++++++++++++++++++-----
 boot.S               | 27 ---------------------
 demo_functionality.c | 26 ++------------------
 interrupt_vector.S   | 53 +++++++++++++++++++++++++++++------------
 interrupts.c         | 55 +++++++++++++++++++++++++++++++++++-------
 kernel.c             | 44 ----------------------------------
 kernel_stage1.S      | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 kernel_stage1.ld     | 27 +++++++++++++++++++++
 kernel_stage2.ld     | 52 ++++++++++++++++++++++++++++++++++++++++
 linker.ld            | 47 ------------------------------------
 memory.h             | 43 ++++++++++++++++++++++-----------
 setup.c              | 41 ++++++++++++++++++++++++++++++++
 12 files changed, 325 insertions(+), 186 deletions(-)
 delete mode 100644 boot.S
 delete mode 100644 kernel.c
 create mode 100644 kernel_stage1.S
 create mode 100644 kernel_stage1.ld
 create mode 100644 kernel_stage2.ld
 delete mode 100644 linker.ld
 create mode 100644 setup.c

(limited to 'linker.ld')

diff --git a/Makefile b/Makefile
index 29efa86..68368a5 100644
--- a/Makefile
+++ b/Makefile
@@ -1,8 +1,10 @@
-CFLAGS=-mcpu=cortex-a7 -ffreestanding -std=gnu11 -Wall -Wextra -O2 -fPIC -I.
+CFLAGS=-mcpu=cortex-a7 -ffreestanding -std=gnu11 -Wall -Wextra -O2 -I.
 ELFFLAGS=-nostdlib -lgcc
 
 ARM_OBJECTS=kernel.o paging.o demo_functionality.o PL0_test.o uart.o loader_stage1.o loader_stage2.o
 
+KERNEL_STAGE2_OBJECTS=setup.o interrupt_vector.o interrupts.o uart.o demo_functionality.o paging.o ramfs_embeddable.o ramfs.o
+
 RAMFS_FILES=PL_0_test.img
 
 all : kernel.img
@@ -10,20 +12,32 @@ all : kernel.img
 %.o : %.c
 	arm-none-eabi-gcc $(CFLAGS) -c $^ -o $@
 
-%.o : %.S
-	arm-none-eabi-as -mcpu=cortex-a7 $^ -o $@
-
 %.img : %.elf
 	arm-none-eabi-objcopy $^ -O binary $@
 
+%.o : %.S
+	arm-none-eabi-as -mcpu=cortex-a7 $^ -o $@
+
 %_embeddable.o : %.img
 	arm-none-eabi-objcopy -I binary -O elf32-littlearm -B arm --rename-section .data=.rodata $^ $@
 
 PL_0_test.elf : PL0_test.o uart.o
 	arm-none-eabi-gcc -T PL0_test.ld -o $@ $(ELFFLAGS) $^
 
-kernel.elf : boot.o kernel.o uart.o demo_functionality.o paging.o interrupt_vector.o interrupts.o ramfs_embeddable.o ramfs.o
-	arm-none-eabi-gcc -T linker.ld -o $@ $(ELFFLAGS) $^
+kernel_stage1.o : kernel_stage1.S kernel_stage2.img
+	arm-none-eabi-as -mcpu=cortex-a7 $< -o $@
+
+kernel.elf : kernel_stage1.ld kernel_stage1.o
+	arm-none-eabi-gcc -T $< -o $@ $(ELFFLAGS) kernel_stage1.o
+
+kernel.img : kernel.elf
+	arm-none-eabi-objcopy $^ -O binary $@
+
+kernel_stage2.elf : kernel_stage2.ld $(KERNEL_STAGE2_OBJECTS)
+	arm-none-eabi-gcc -T $< -o $@ $(ELFFLAGS) $(KERNEL_STAGE2_OBJECTS)
+
+#kernel.elf : boot.o kernel.o uart.o demo_functionality.o paging.o interrupt_vector.o interrupts.o ramfs_embeddable.o ramfs.o
+#	arm-none-eabi-gcc -T linker.ld -o $@ $(ELFFLAGS) $^
 
 loader_stage2.elf : loader_stage2.o uart.o
 	arm-none-eabi-gcc -T loader_stage2_linker.ld -o $@ $(ELFFLAGS) $^
@@ -42,6 +56,9 @@ loader.img : loader.elf
 qemu-elf : kernel.elf
 	qemu-system-arm -m 256 -M raspi2 -serial stdio -kernel $^
 
+qemu-img : kernel.img
+	qemu-system-arm -m 256 -M raspi2 -serial stdio -kernel $^
+
 qemu-bin : loader.img kernel.img pipe_image
 	./pipe_image --stdout | qemu-system-arm -m 256 -M raspi2 -serial stdio -kernel $<
 
diff --git a/boot.S b/boot.S
deleted file mode 100644
index 593ed11..0000000
--- a/boot.S
+++ /dev/null
@@ -1,27 +0,0 @@
-// armv7 mode
- 
-// Entry point for the kernel.
-// r15 -> should begin execution at 0x8000.
-// r0 -> 0x00000000
-// r1 -> 0x00000C42
-// r2 -> 0x00000100 - start of ATAGS
-// preserve these registers as argument for kernel_main
-	
-.global _boot // make entry point label global
-_boot:
-        // Only let the first core execute
-        mrc p15, 0, r3, c0, c0, 5
-        and r3, r3, #3
-        cmp r3, #0
-        beq proceed
-	// this is a kind of blef - races can theoretically still occur
-	// when the main core overwrites this part of memory
-	wfe
-
-proceed:
-        // Initialize the stack (_stack_top is defined in linker.ld)
-        ldr sp, =_stack_top
- 
-        // Call kernel_main
-        ldr r3, =kernel_main
-        bx r3
diff --git a/demo_functionality.c b/demo_functionality.c
index 4b002d6..420639b 100644
--- a/demo_functionality.c
+++ b/demo_functionality.c
@@ -53,7 +53,7 @@ void demo_current_mode(void)
   uart_puts(mode_name);
 }
 
-#define TRANSLATION_TABLE						\
+#define TRANSLATION_TABLE					     \
   ((short_section_descriptor_t volatile*) TRANSLATION_TABLE_BASE)
 
 extern char
@@ -144,29 +144,7 @@ void demo_go_unprivileged(void)
   write_SPSR(new_SPSR);
 
   uart_puts("All ready, jumping to PL0 code\n\r");
-  
+
   asm volatile("ldm %0, {r0 - r15} ^" ::
 	       "r" (PL0_regs));
 }
-
-extern char
-  __interrupts_start,
-  __interrupts_end,
-  __interrupts_size;
-
-extern void (*volatile system_reentry_point)(void);
-
-void system_reentry(void)
-{
-  uart_puts("re-entered system");
-  while(1);
-}
-
-void demo_setup_interrupts(void)
-{
-  system_reentry_point = system_reentry;
-
-  for (size_t i = 0; i < (size_t) &__interrupts_size; i++)
-    ((volatile char*) 0)[i] =
-      (&__interrupts_start)[i];
-}
diff --git a/interrupt_vector.S b/interrupt_vector.S
index d20bf6d..6037b7c 100644
--- a/interrupt_vector.S
+++ b/interrupt_vector.S
@@ -1,22 +1,45 @@
-.section ".interrupts.vector"
-
-.global abort_handler
-.local generic_handler	
-.global _interrupt_vectors
 _interrupt_vectors:
-	b generic_handler
-	b generic_handler
-	b generic_handler
+	b reset_handler_caller
+	b undef_handler_caller
+	b svc_handler_caller
 	b abort_handler_caller
 	b abort_handler_caller
-	b generic_handler
-	b generic_handler
-
-.section ".interrupts.text"
+	b generic_handler_caller
+	b irq_handler_caller
+	b fiq_handler_caller
+	
+reset_handler_caller:
+	ldr sp, =_stack_top
+	ldr r5, =reset_handler
+	bx r5
+	
+undef_handler_caller:
+	ldr sp, =_stack_top
+	ldr r5, =undefined_instruction_vector
+	bx r5
 
-generic_handler:
-	b generic_handler
+svc_handler_caller:
+	ldr sp, =_stack_top
+	ldr r5, =supervisor_call_handler
+	bx r5
+	
 abort_handler_caller:
-	mov sp, #0x8000
+	ldr sp, =_stack_top
 	ldr r5, =abort_handler
 	bx r5
+
+generic_handler_caller:
+	ldr sp, =_stack_top
+	ldr r5, =generic_handler
+	bx r5
+
+irq_handler_caller:
+	ldr sp, =_stack_top
+	ldr r5, =irq_handler
+	bx r5
+
+fiq_handler_caller:
+	ldr sp, =_stack_top
+	ldr r5, =fiq_handler
+	bx r5
+	
diff --git a/interrupts.c b/interrupts.c
index 6952f89..1b0590a 100644
--- a/interrupts.c
+++ b/interrupts.c
@@ -1,10 +1,20 @@
 #include "uart.h"
-/**
-    @brief The undefined instruction interrupt handler
 
-    If an undefined instruction is encountered, the CPU will start
-    executing this function. Just trap here as a debug solution.
-*/
+void setup(void);
+
+void reset_handler(void)
+{
+  static _Bool setup_done;
+  
+  if (!setup_done)
+    setup();
+
+  setup_done = 1;
+
+  // TODO do something here
+  while(1);
+}
+
 void
 __attribute__((interrupt("UNDEF")))
 __attribute__((section(".interrupts.text")))
@@ -17,13 +27,40 @@ undefined_instruction_vector(void)
     }
 }
 
-void __attribute__((section(".interrupts.data")))
-(*system_reentry_point) (void);
+void supervisor_call_handler(void)
+{
+  uart_puts("something svc happened\n\r");
+
+  while(1);
+}
 
 void
 __attribute__((interrupt("ABORT")))
-__attribute__((section(".interrupts.text")))
 abort_handler(void)
 {
-  system_reentry_point();
+  uart_puts("re-entered system\n\r");
+
+  while(1);
+}
+
+void generic_handler(void)
+{
+  uart_puts("something weird happened\n\r");
+
+  while(1);
+}
+
+void irq_handler(void)
+{
+  uart_puts("irq happened\n\r");
+
+  while(1);
+}
+
+void fiq_handler(void)
+{
+  uart_puts("fiq happened\n\r");
+
+  while(1);
 }
+
diff --git a/kernel.c b/kernel.c
deleted file mode 100644
index 719ceff..0000000
--- a/kernel.c
+++ /dev/null
@@ -1,44 +0,0 @@
-#include "uart.h"
-#include "demo_functionality.h"
-#include "paging.h"
-
-void kernel_main(void)
-{
-  uart_init();
-
-  // When we attach screen session after loading kernel with socat
-  // we miss kernel's greeting... So we'll make the kernel wait for
-  // one char we're going to send from within screen
-  uart_getc();
-  
-  uart_puts("Hello, kernel World!\r\n");
-
-  // prints some info
-  demo_paging_support();
-
-  // prints some info
-  demo_current_mode();
-
-  // prints some info and sets upp translation table, turns on MMU
-  setup_flat_map();
-
-  demo_setup_PL0();
-
-  demo_setup_interrupts();
-  
-  // prints some info and sets up a section for PL0 code, loads a blob
-  // there and jumps to it... never, ever, ever returns
-  demo_go_unprivileged();
-  
-  while(1);
-  
-  while (1)
-    {
-      char c = uart_getc();
-
-      uart_putc(c);
-      
-      if (c == '\r')
-	uart_putc('\n');
-    }
-}
diff --git a/kernel_stage1.S b/kernel_stage1.S
new file mode 100644
index 0000000..1e0f614
--- /dev/null
+++ b/kernel_stage1.S
@@ -0,0 +1,67 @@
+/* arm mode, cortex-a7 compatibility
+ *
+ * _boot is entry point for the kernel.
+ *
+ * Kernel copies it's embedded stage 2 to address 0x0 and jumps to
+ * it (to the reset handler). Registers r0 - r2 are arguments for
+ * the kernel, but we're not using them for now.
+ *
+ * This file is based on (and almost identical with) loader_stage1.S
+ */
+	
+.global _boot
+_boot:
+        // Only let the first core execute
+        mrc p15, 0, r3, c0, c0, 5
+        and r3, r3, #3
+        cmp r3, #0
+        beq proceed
+	// this is a kind of blef - races can theoretically still
+	// occur when the main core overwrites this part of memory
+	wfe
+
+proceed:
+	// copy stage2 of the kernel to address 0x0
+
+	// first, load address of stage2_start to r3 (a PIC way)
+	adr r3, stage2_start
+
+	// load destination address for stage2 code to r4
+	mov r4, #0
+
+	// load blob size to r5
+	// The size might get too big for an immediate value, so
+	// we load it from memory.
+	adr r5, blob_size
+	ldr r5, [r5]
+
+	// r6 is the counter - counts the bytes copied
+	mov r6, #0
+
+	// This initial piece of code might get overwritten when we
+	// copy stage2, so the actual copying loop shall be after
+	// stage2 blob. We want this asm code to be PIC, so we're
+	// computing address of stage2_end into r7.
+	add r7, r3, r5
+	bx r7
+	
+blob_size:
+	.word stage2_end - stage2_start
+
+.align 4
+stage2_start:
+	.incbin "kernel_stage2.img"
+stage2_end:
+
+	// each word of the blob is loaded to r7 and stored
+	// from r7 to it's destination in a loop
+loop:
+	ldr r7, [r3, r6]
+	str r7, [r4, r6]
+	add r6, r6, #4
+	cmp r6, r5
+	blo loop
+	
+        // Call stage2 of the kernel (branch to 0x0,
+	// which is the reset handler).
+        bx r4
diff --git a/kernel_stage1.ld b/kernel_stage1.ld
new file mode 100644
index 0000000..3130634
--- /dev/null
+++ b/kernel_stage1.ld
@@ -0,0 +1,27 @@
+ENTRY(_boot) /* defined in boot.S; qemu needs it to run elf file */
+
+/* Code starts at  0x8000 - that's where RPis in 32-bit mode load
+ * kernel at. My experiments do, however, show, that qemu emulating
+ * RPi2 loads the kernel at 0x10000! (took some pain to find out).
+ * rpi-open-firmware, on the other hand, loads kernel at 0x2000000!
+ * This is not really a problem, since:
+ *   1. We can use our bootloader to load the kernel at 0x8000
+ *   2. We've rewritten stage 1 of both bootloader and kernel in
+ *      careful assembly, so that they should work regardless of
+ *      where they are loaded.
+ *   3. In qemu, we can load kernel.elf instead of raw binary
+ *      (qemu will do the right thing then)
+ */
+
+SECTIONS
+{
+
+	. = 0x8000;
+
+	__start = .;
+	.kernel_stage1 :
+	{
+		KEEP(kernel_stage1.o)
+	}
+	__end = .;
+}
diff --git a/kernel_stage2.ld b/kernel_stage2.ld
new file mode 100644
index 0000000..d3a23bf
--- /dev/null
+++ b/kernel_stage2.ld
@@ -0,0 +1,52 @@
+/* This sesond stage of the kernel is run from address 0x0 */
+
+TRANSLATION_TABLE_SIZE = 4096 * 4;
+MMU_SECTION_SIZE = 1 << 20;
+
+SECTIONS
+{
+
+	. = 0x0;
+
+	__start = .;
+	.kernel_stage2 :
+	{
+		KEEP(interrupt_vector.o)
+		. = ALIGN(4);
+		ramfs_embeddable.o
+		(*)
+	}
+	__end = .;
+
+	. = ALIGN(1 << 14);
+	
+	.translation_table (NOLOAD) :
+	{
+		_translation_table_start = .;
+		
+		. = . + TRANSLATION_TABLE_SIZE;
+
+		_translation_table_end = .;
+	}
+
+	. = ALIGN(1 << 20);
+	. = . + MMU_SECTION_SIZE;
+	
+	.stack (NOLOAD) :
+	{
+		_stack_start = .;
+		
+		. = . + MMU_SECTION_SIZE;
+
+		_stack_top = .;
+	}
+
+	.unprivileged_memory (NOLOAD) :
+	{
+		_unprivileged_memory_start = .;
+		
+		. = . + MMU_SECTION_SIZE;
+
+		_unprivileged_memory_end = .;
+	}
+}
diff --git a/linker.ld b/linker.ld
deleted file mode 100644
index 444bbf6..0000000
--- a/linker.ld
+++ /dev/null
@@ -1,47 +0,0 @@
-ENTRY(_boot) /* defined in boot.S; qemu needs it to run elf file */
- 
-SECTIONS
-{
-    /* Starts at  0x8000 - that's where RPis in 32-bit mode load */
-    /* kernel at. My experiments do, however, show, that qemu */
-    /* emulating RPi2 loads the kernel at 0x10000! (took some pain */
-    /* to find out). rpi-open-firmware, on the other hand, loads */
-    /* kernel at 0x2000000! */
-    /* This is not really a problem, since: */
-    /*   1. We can use our bootloader to load the kernel at 0x8000 */
-    /*   2. Stage 1 of the bootloader is written in careful */
-    /*      assembly, so that the loader itself should work */
-    /*      regardless of where it is loaded. */
-    /*   3. In qemu, we can load kernel.elf instead of raw binary */
-    /*      (qemu will do the right thing then) */
-
-    . = 0x8000;
-
-    /* RPi in 64-bit mode uses address 0x80000 instead */
-    
-    __start = .;
-    .kernel :
-    {
-        __kernel_start = .;
-	KEEP(boot.o)
-	. = ALIGN(4);
-	ramfs_embeddable.o
-	*(EXCLUDE_FILE (libkernel.o interrupt_vector.o interrupts.o) *)
-	__kernel_end = .;
-    }
-    __kernel_size = __kernel_end - __kernel_start;
-
-    .interrupts :
-    {
-	__interrupts_start = .;
-	KEEP(*(.interrupts.vector))
-	interrupt_vector.o
-	interrupts.o
-    	__interrupts_end = .;
-    }
-    __interrupts_size = __interrupts_end - __interrupts_start;
-    
-    __end = .;
-
-    _stack_top = __start;
-}
diff --git a/memory.h b/memory.h
index e4493e2..adc3bc0 100644
--- a/memory.h
+++ b/memory.h
@@ -1,7 +1,10 @@
 #ifndef MEMORY_H
 #define MEMORY_H
 
-#define POWER_OF_2(EXP) (((uint32_t) 1) << EXP)
+// These macros were heavily used b4 I moved all the address
+// computation to the linker script. Now I'm just keeping them
+// in case they're needed for something else :)
+#define POWER_OF_2(EXP) (((size_t) 1) << EXP)
 
 #define ALIGN_POWER_OF_2(ADDR, EXP)				\
   (((ADDR - 1) & ~(POWER_OF_2(EXP) - 1)) + POWER_OF_2(EXP))
@@ -10,33 +13,45 @@
 
 #define ALIGN_SECTION(ADDR) ALIGN_POWER_OF_2(ADDR, 20)
 
-#define INTERRUPT_VECTOR_TABLE_START ((uint32_t) 0x0)
 
-#define STACK_START ((uint32_t) 0x4000)
-#define STACK_END   ((uint32_t) 0x8000)
+// memory layout
+
+#define INTERRUPT_VECTOR_TABLE_START ((uint32_t) 0x0)
 
+// all those symbols are defined in the linker script
 extern const char __end;
 extern const char __start;
+extern const char _translation_table_start;
+extern const char _translation_table_end;
+extern const char _stack_start;
+extern const char _stack_top;
+extern const char _unprivileged_memory_start;
+extern const char _unprivileged_memory_end;
 
-#define KERNEL_START ((uint32_t) &__start) // this is 0x8000
-#define KERNEL_END   ((uint32_t) &__end)
+#define KERNEL_START ((size_t) &__start) // this is 0x0
+#define KERNEL_END   ((size_t) &__end)
 
 // first 2^14 aligned address after the kernel
-#define TRANSLATION_TABLE_BASE ALIGN_POWER_OF_2(KERNEL_END, 14)
-
-#define TRANSLATION_TABLE_END				\
-  (TRANSLATION_TABLE_BASE + (uint32_t) (4096 * 4))
+#define TRANSLATION_TABLE_BASE ((size_t) &_translation_table_start)
+#define TRANSLATION_TABLE_END  ((size_t) &_translation_table_end)
 
-#define PRIVILEGED_MEMORY_END ALIGN_SECTION(TRANSLATION_TABLE_END)
+// first section after the translation table is left unused;
+// the next section is used as the stack
+#define STACK_START ((size_t) &_stack_start)
+#define STACK_END   ((size_t) &_stack_top)
 
-#define UNPRIVILEGED_MEMORY_START PRIVILEGED_MEMORY_END
+#define PRIVILEGED_MEMORY_END STACK_END
 
+#define UNPRIVILEGED_MEMORY_START				\
+  ((size_t) &_unprivileged_memory_start)  // equal to STACK_END
 #define UNPRIVILEGED_MEMORY_END			\
-  (UNPRIVILEGED_MEMORY_START + SECTION_SIZE)
+  ((size_t) &_unprivileged_memory_end)
 
-#define PL0_SECTION_NUMBER ((uint32_t) 0b101010101010)
+#define PL0_SECTION_NUMBER ((size_t) 0xaaa)
 
 #define VIRTUAL_PL0_MEMORY_START (PL0_SECTION_NUMBER << 20)
+#define VIRTUAL_PL0_MEMORY_END			\
+  (VIRTUAL_PL0_MEMORY_START + SECTION_SIZE)
 
 #endif // MEMORY_H
 
diff --git a/setup.c b/setup.c
new file mode 100644
index 0000000..48df825
--- /dev/null
+++ b/setup.c
@@ -0,0 +1,41 @@
+#include "uart.h"
+#include "demo_functionality.h"
+#include "paging.h"
+
+void setup(void)
+{
+  uart_init();
+
+  // When we attach screen session after loading kernel with socat
+  // we miss kernel's greeting... So we'll make the kernel wait for
+  // one char we're going to send from within screen
+  uart_getc();
+  
+  uart_puts("Hello, kernel World!\r\n");
+
+  // prints some info
+  demo_paging_support();
+
+  // prints some info
+  demo_current_mode();
+
+  // prints some info and sets upp translation table, turns on MMU
+  setup_flat_map();
+
+  // prints some info and sets up a section for PL0 code,
+  // loads a blob there 
+  demo_setup_PL0();
+
+  // jumps to unprivileged code... never, ever, ever returns
+  demo_go_unprivileged();
+  
+  while (1)
+    {
+      char c = uart_getc();
+
+      uart_putc(c);
+      
+      if (c == '\r')
+	uart_putc('\n');
+    }
+}
-- 
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