sos

commit aab5207bbd3c17a735529e96624e47eedfee596f
parent 4fe48287b862385075279312d8863c37be3b63ad
Author: Stefan <misc@stefan-koch.name>
Date:   Mon, 19 Oct 2015 21:53:39 +0200

setup GDT from kernel

Diffstat:
M
Makefile
 | 
8
+++++---
R
boot.asm -> arch/x86/boot.asm
 | 
0

A
arch/x86/gdt.asm
 | 
14
++++++++++++++
A
arch/x86/gdt.c
 | 
29
+++++++++++++++++++++++++++++
A
arch/x86/gdt.h
 | 
27
+++++++++++++++++++++++++++
M
kernel.c
 | 
4
++++

6 files changed, 79 insertions(+), 3 deletions(-)
diff --git a/Makefile b/Makefile
@@ -6,9 +6,11 @@ GCCFLAGS = -std=gnu99 -ffreestanding -O2 -Wall -Wextra
 all: image kernel kernel-install
 
 kernel:
-	$(ASM) boot.asm -o boot.o -f elf
+	$(ASM) arch/x86/boot.asm -o arch/x86/boot.o -f elf
+	$(ASM) arch/x86/gdt.asm -o arch/x86/gdt_asm.o -f elf
 	$(GCC) -c kernel.c -o kernel.o $(GCCFLAGS)
-	$(GCC) -T kernel.ld -o sos-kernel.img -ffreestanding -O2 -nostdlib boot.o kernel.o -lgcc
+	$(GCC) -c arch/x86/gdt.c -o arch/x86/gdt.o $(GCCFLAGS)
+	$(GCC) -T kernel.ld -o sos-kernel.img -ffreestanding -O2 -nostdlib arch/x86/boot.o kernel.o arch/x86/gdt_asm.o arch/x86/gdt.o -lgcc
 
 kernel-install:
 	sudo losetup /dev/loop1 sos.img -o 1048576
@@ -26,13 +28,13 @@ image:
 	sudo mke2fs /dev/loop1
 	sudo mount /dev/loop1 /mnt
 	sudo grub-install --root-directory=/mnt --no-floppy --modules="normal ext2 part_msdos multiboot" /dev/loop0
-	sudo cp sos-kernel.img /mnt/boot/
 	sudo cp grub/* /mnt/boot/grub/
 	sudo losetup -d /dev/loop0
 	sudo umount /mnt
 	sudo losetup -d /dev/loop1
 	
 clean:
+	rm arch/x86/*.o
 	rm *.o
 	rm sos-kernel.img
 	rm sos.img
diff --git a/boot.asm b/arch/x86/boot.asm
diff --git a/arch/x86/gdt.asm b/arch/x86/gdt.asm
@@ -0,0 +1,14 @@
+section .text
+extern gdt_desc
+global gdt_install
+gdt_install:
+    lgdt [gdt_desc]
+    jmp 08h:reload_cs
+reload_cs:
+    mov eax, 10h
+    mov ds, eax
+    mov es, eax
+    mov fs, eax
+    mov gs, eax
+    mov ss, eax
+    ret
diff --git a/arch/x86/gdt.c b/arch/x86/gdt.c
@@ -0,0 +1,29 @@
+#include <stdint.h>
+#include "gdt.h"
+
+extern void gdt_install();
+
+void gdt_set_entry(unsigned int pos, uint32_t base, uint32_t limit,
+        uint8_t access_rights, uint8_t flags)
+{
+    gdt[pos].base_lower = base & 0xffff;
+    gdt[pos].base_middle = (base >> 16) & 0xff;
+    gdt[pos].base_higher = (base >> 24) & 0xffff;
+
+    gdt[pos].limit_lower = limit & 0xffff;
+    gdt[pos].flags_limit_higher = ((flags << 4) & 0xf0) | ((limit >> 16) & 0x0f); 
+
+    gdt[pos].access_rights = access_rights;
+}
+
+void gdt_setup()
+{
+    gdt_desc.limit = GDT_ENTRIES * sizeof(struct gdt_entry) - 1;
+    gdt_desc.base = (uint32_t) (uintptr_t) gdt;
+
+    gdt_set_entry(0, 0, 0, 0, 0);
+    gdt_set_entry(1, 0, 0xfffff, 0x9a, 0xcf);
+    gdt_set_entry(2, 0, 0xfffff, 0x92, 0xcf);
+    
+    gdt_install();
+}
diff --git a/arch/x86/gdt.h b/arch/x86/gdt.h
@@ -0,0 +1,27 @@
+#ifndef GDT_H
+#define GDT_H
+
+#include <stdint.h>
+
+#define GDT_ENTRIES 3
+
+struct gdt_entry {
+    uint16_t limit_lower;
+    uint16_t base_lower;
+    uint8_t base_middle;
+    uint8_t access_rights;
+    uint8_t flags_limit_higher;
+    uint8_t base_higher;
+} __attribute__((packed));
+
+struct gdt_description {
+    uint16_t limit;
+    uint32_t base;
+} __attribute__((packed));
+
+struct gdt_entry gdt[GDT_ENTRIES];
+struct gdt_description gdt_desc;
+
+void gdt_setup();
+
+#endif
diff --git a/kernel.c b/kernel.c
@@ -1,5 +1,9 @@
+#include "arch/x86/gdt.h"
+
 void kernel_main()
 {
+    gdt_setup();
+
     char *vidmem = (char*) 0xb8000;
     vidmem[0] = 'H';
     vidmem[2] = 'e';