Higher half, c main

src/kernel/Link.ld

@@ -1,10 +1,29 @@
 ENTRY(_start)
 
+KERNEL_OFFSET = 0xFFFFFF8000000000;
+KERNEL_START = 0x10000;
+
 SECTIONS
 {
-    .text :
+    . = KERNEL_START + KERNEL_OFFSET;
+    kernel_start = .;
+    .text : AT(ADDR(.text) - KERNEL_OFFSET)
     {
         *(.multiboot)
         *(.text)
     }
+    .rodata : AT(ADDR(.rodata) - KERNEL_OFFSET)
+    {
+        *(.rodata*)
+    }
+    .data : AT(ADDR(.data) - KERNEL_OFFSET)
+    {
+        *(.data)
+    }
+    .bss : AT(ADDR(.bss) - KERNEL_OFFSET)
+    {
+        *(.COMMON)
+        *(.bss)
+    }
+    kernel_end = .;
 }

src/kernel/Makefile

@@ -7,7 +7,7 @@ CC := ${TARGET}-gcc
 SRC := $(wildcard **/*.[cS])
 OBJ := $(patsubst %, %.o, $(basename $(SRC)))
 
-CFLAGS := -Wall -Wextra -pedantic -ffreestanding
+CFLAGS := -Wall -Wextra -pedantic -ffreestanding -mcmodel=large
 CFLAGS += -ggdb -O0
 ASFLAGS += -ggdb
 CPPFLAGS += -I include

src/kernel/boot/boot.S

@@ -17,7 +17,7 @@ _start:
     cli
 
     // Temporary stack for booting
-    mov esp, offset BootStack
+    mov esp, offset V2P(BootStack)
 
     // Enable Page Address Extension
     mov eax, cr4
@@ -25,7 +25,7 @@ _start:
     mov cr4, eax
 
     // Load Page Table (defined in boot/boot_PT.S)
-    mov eax, offset BootP4
+    mov eax, offset V2P(BootP4)
     mov cr3, eax
 
     // Enable Long Mode
@@ -40,10 +40,10 @@ _start:
     mov cr0, eax
 
     // Load GDT (defined in cpu/gdt.c)
-    lgdt [GDTp]
+    lgdt [V2P(GDTp)]
 
     // Jump into long mode
-    jmp 0x8:long_mode_start
+    jmp 0x8:V2P(long_mode_start)
 
 .code64
 long_mode_start:
@@ -54,4 +54,36 @@ long_mode_start:
     mov ds, eax
     mov es, eax
 
+    movabs rax, offset upper_memory
+    jmp rax
+
+upper_memory:
+    movabs rax, offset BootStack
+    mov rsp, rax
+
+    mov rax, 0
+    movabs [BootP4], rax
+
+    mov rax, cr3
+    mov cr3, rax
+
+    movabs rax, offset GDTp
+    lgdt [rax]
+    mov rax, 0
+    mov ss, eax
+    mov ds, eax
+    mov es, eax
+
+    movabs rax, offset .reload_cs
+    pushq 0x8
+    push rax
+    retfq
+
+.reload_cs:
+
+.extern kmain
+    movabs rax, offset kmain
+    call rax
+    
+    hlt
     jmp $

src/kernel/boot/boot_PT.S

@@ -6,17 +6,18 @@
 .global BootP4
 
 BootP4:
-    .quad offset BootP3 + (PAGE_PRESENT | PAGE_WRITE)
-    .rept ENTRIES_PER_PT - 1
+    .quad offset V2P(BootP3) + (PAGE_PRESENT | PAGE_WRITE)
+    .rept ENTRIES_PER_PT - 2
         .quad 0
     .endr
+    .quad offset V2P(BootP3) + (PAGE_PRESENT | PAGE_WRITE)
 BootP3:
-    .quad offset BootP2 + (PAGE_PRESENT | PAGE_WRITE)
+    .quad offset V2P(BootP2) + (PAGE_PRESENT | PAGE_WRITE)
     .rept ENTRIES_PER_PT - 1
         .quad 0
     .endr
 BootP2:
-    .quad offset BootP1 + (PAGE_PRESENT | PAGE_WRITE)
+    .quad offset V2P(BootP1) + (PAGE_PRESENT | PAGE_WRITE)
     .rept ENTRIES_PER_PT - 1
         .quad 0
     .endr

src/kernel/boot/kmain.c

@@ -0,0 +1,25 @@
+#include <memory.h>
+
+void clear_screen()
+{
+    unsigned char *vidmem = P2V(0xB8000);
+    for(int i=0; i < 80*24*2; i++)
+        *vidmem++ = 0;
+}
+
+void print_string(char *str)
+{
+    unsigned char *vidmem = P2V(0xB8000);
+    while(*str)
+    {
+        *vidmem++ = *str++;
+        *vidmem++ = 0x7;
+    }
+}
+
+void kmain()
+{
+    clear_screen();
+    print_string("Hello from c, world!");
+    for(;;);
+}

src/kernel/include/memory.h

@@ -1,5 +1,16 @@
 #pragma once
 
+#define KERNEL_OFFSET 0xFFFFFF8000000000
+
+#ifdef __ASSEMBLER__
+#define V2P(a) ((a) - KERNEL_OFFSET)
+#define P2V(a) ((a) + KERNEL_OFFSET)
+#else
+#include <stdint.h>
+#define V2P(a) ((uintptr_t)(a) &~KERNEL_OFFSET)
+#define P2V(a) ((void *)((uintptr_t)(a) | KERNEL_OFFSET))
+#endif
+
 #define PAGE_SIZE 0x1000
 
 #define PAGE_PRESENT 0x001