diff --git a/Makefile b/Makefile index cb9b5cb..5fc7c7b 100644 --- a/Makefile +++ b/Makefile @@ -1,5 +1,5 @@ # Define the object files -OBJS = bin/boot.o bin/kernel.o bin/idt.o bin/isr.o bin/screen.o bin/utils.o bin/string.o bin/stdio.o +OBJS = bin/boot.o bin/kernel.o bin/idt.o bin/isr.o bin/screen.o bin/utils.o bin/string.o bin/stdio.o bin/gdt.o # Define the compiler and assembler CC = gcc -D__is_katauos @@ -45,6 +45,9 @@ bin/string.o: src/string.c bin/stdio.o: src/stdio.c $(CC) $(CFLAGS) -c $< -o $@ +bin/gdt.o: src/gdt.c + $(CC) $(CFLAGS) -c $< -o $@ + clean: rm -rf bin/ rm -f $(OUTPUT) diff --git a/include/gdt.h b/include/gdt.h new file mode 100644 index 0000000..bd8820e --- /dev/null +++ b/include/gdt.h @@ -0,0 +1,6 @@ +#ifndef GDT_H +#define GDT_H + +void gdt_install(); + +#endif diff --git a/src/gdt.c b/src/gdt.c new file mode 100644 index 0000000..47da49a --- /dev/null +++ b/src/gdt.c @@ -0,0 +1,84 @@ +#include "../include/gdt.h" +#include "../include/stdio.h" +#include + +struct gdt_entry { + uint64_t descriptor; +}; + +struct gdt_entry gdt[5]; + +// Each define here is for a specific flag in the descriptor. +// Refer to the intel documentation for a description of what each one does. +#define SEG_DESCTYPE(x) ((x) << 0x04) // Descriptor type (0 for system, 1 for code/data) +#define SEG_PRES(x) ((x) << 0x07) // Present +#define SEG_SAVL(x) ((x) << 0x0C) // Available for system use +#define SEG_LONG(x) ((x) << 0x0D) // Long mode +#define SEG_SIZE(x) ((x) << 0x0E) // Size (0 for 16-bit, 1 for 32) +#define SEG_GRAN(x) ((x) << 0x0F) // Granularity (0 for 1B - 1MB, 1 for 4KB - 4GB) +#define SEG_PRIV(x) (((x) & 0x03) << 0x05) // Set privilege level (0 - 3) + +#define SEG_DATA_RD 0x00 // Read-Only +#define SEG_DATA_RDA 0x01 // Read-Only, accessed +#define SEG_DATA_RDWR 0x02 // Read/Write +#define SEG_DATA_RDWRA 0x03 // Read/Write, accessed +#define SEG_DATA_RDEXPD 0x04 // Read-Only, expand-down +#define SEG_DATA_RDEXPDA 0x05 // Read-Only, expand-down, accessed +#define SEG_DATA_RDWREXPD 0x06 // Read/Write, expand-down +#define SEG_DATA_RDWREXPDA 0x07 // Read/Write, expand-down, accessed +#define SEG_CODE_EX 0x08 // Execute-Only +#define SEG_CODE_EXA 0x09 // Execute-Only, accessed +#define SEG_CODE_EXRD 0x0A // Execute/Read +#define SEG_CODE_EXRDA 0x0B // Execute/Read, accessed +#define SEG_CODE_EXC 0x0C // Execute-Only, conforming +#define SEG_CODE_EXCA 0x0D // Execute-Only, conforming, accessed +#define SEG_CODE_EXRDC 0x0E // Execute/Read, conforming +#define SEG_CODE_EXRDCA 0x0F // Execute/Read, conforming, accessed + +#define GDT_CODE_PL0 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \ + SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \ + SEG_PRIV(0) | SEG_CODE_EXRD + +#define GDT_DATA_PL0 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \ + SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \ + SEG_PRIV(0) | SEG_DATA_RDWR + +#define GDT_CODE_PL3 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \ + SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \ + SEG_PRIV(3) | SEG_CODE_EXRD + +#define GDT_DATA_PL3 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \ + SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \ + SEG_PRIV(3) | SEG_DATA_RDWR + +void create_descriptor(uint32_t base, uint32_t limit, uint16_t flag) +{ + uint64_t descriptor; + + // Create the high 32 bit segment + descriptor = limit & 0x000F0000; // set limit bits 19:16 + descriptor |= (flag << 8) & 0x00F0FF00; // set type, p, dpl, s, g, d/b, l and avl fields + descriptor |= (base >> 16) & 0x000000FF; // set base bits 23:16 + descriptor |= base & 0xFF000000; // set base bits 31:24 + + // Shift by 32 to allow for low part of segment + descriptor <<= 32; + + // Create the low 32 bit segment + descriptor |= base << 16; // set base bits 15:0 + descriptor |= limit & 0x0000FFFF; // set limit bits 15:0 + + printf("0x%.16llX\n", descriptor); +} + +void gdt_install() +{ + create_descriptor(0, 0, 0); + create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL0)); + create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL0)); + create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL3)); + create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL3)); + + __asm__ __volatile__("lgdt (%0)" : : "r" (gdt)); + printf("gdt_install done\n"); +} diff --git a/src/kernel.c b/src/kernel.c index aaa0583..9bc25c6 100644 --- a/src/kernel.c +++ b/src/kernel.c @@ -1,4 +1,5 @@ #include "../include/isr.h" +#include "../include/gdt.h" #include "../include/screen.h" #include "../include/stdio.h" #include "../include/utils.h" @@ -18,6 +19,7 @@ void kmain() { terminal_initialize(); printf("KatauOS booting up\n"); + gdt_install(); isr_install(); printf("Kernel init sequence completed\n");