Merge pull request #1 from Azomasiel/gdt
Memory management: Global Descriptor Table
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commit
439394c667
1
.bochsrc
1
.bochsrc
@ -11,6 +11,7 @@ clock: sync=realtime
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ata0: enabled=1, ioaddr1=0x1f0, ioaddr2=0x3f0, irq=14
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ata0-master: type=cdrom, path="k.iso", status=inserted
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boot: cdrom
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magic_break: enabled=1
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# write serial logs to stdout
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com1: enabled=1, mode=file, dev=/dev/stdout
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@ -30,7 +30,8 @@ OBJS = \
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libvga.o \
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list.o \
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memory.o \
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serial.o
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serial.o \
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gdt.o
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DEPS = $(OBJS:.o=.d)
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122
k/gdt.c
Normal file
122
k/gdt.c
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@ -0,0 +1,122 @@
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#include "gdt.h"
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static struct gdt gdt = { 0 };
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static void create_kernel_ds()
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{
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struct gdt_entry *entry = gdt.entries + KERNEL_DS_INDEX;
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uint32_t limit = 0xfffff;
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uint32_t base = 0x0;
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entry->granularity = 1;
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entry->db = 1;
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entry->l = 0;
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entry->available = 0;
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entry->present = 1;
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entry->desc_priv = 0;
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entry->desc_type = 1;
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entry->ex = 0;
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entry->dc = 0;
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entry->rw = 1;
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entry->accessed = 0;
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entry->limit_1 = limit & 0xffff;
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entry->limit_2 = (limit >> 16) & 0xf;
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entry->base_1 = base & 0xffff;
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entry->base_2 = (base >> 16) & 0xff;
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entry->base_3 = (base >> 24) & 0xff;
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}
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static void create_kernel_cs()
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{
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struct gdt_entry *entry = gdt.entries + KERNEL_CS_INDEX;
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uint32_t limit = 0xfffff;
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uint32_t base = 0x0;
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entry->granularity = 1;
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entry->db = 1;
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entry->l = 0;
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entry->available = 0;
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entry->present = 1;
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entry->desc_priv = 0;
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entry->desc_type = 1;
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entry->ex = 1;
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entry->dc = 0;
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entry->rw = 1;
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entry->accessed = 0;
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entry->limit_1 = limit & 0xffff;
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entry->limit_2 = (limit >> 16) & 0xf;
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entry->base_1 = base & 0xffff;
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entry->base_2 = (base >> 16) & 0xff;
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entry->base_3 = (base >> 24) & 0xff;
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}
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static void create_gdt()
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{
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create_kernel_ds();
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create_kernel_cs();
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}
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static void load_gdt()
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{
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struct gdt_r gdtr;
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gdtr.addr = (uint32_t)&gdt;
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gdtr.limit = GDT_SIZE - 1;
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asm volatile("lgdt %0\n"
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:
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: "m" (gdtr)
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: "memory");
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}
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static void load_ds()
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{
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struct segment_selector selector;
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selector.index = KERNEL_DS_INDEX;
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selector.table_indicator = 0;
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selector.rpl = 0;
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asm volatile("movw %0, %%ax\n"
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"movw %%ax, %%ds\n"
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"movw %%ax, %%fs\n"
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"movw %%ax, %%gs\n"
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"movw %%ax, %%ss\n"
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:
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: "m" (selector)
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: "ax");
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}
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static void load_cs()
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{
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struct segment_selector selector;
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selector.index = KERNEL_CS_INDEX;
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selector.table_indicator = 0;
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selector.rpl = 0;
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asm volatile("pushl %0\n"
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"pushl $1f\n"
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"lret\n"
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"1:\n"
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:
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: "m" (selector));
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}
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static void reload_segment_selectors()
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{
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load_ds();
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load_cs();
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}
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void init_gdt()
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{
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create_gdt();
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load_gdt();
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reload_segment_selectors();
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}
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52
k/gdt.h
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52
k/gdt.h
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@ -0,0 +1,52 @@
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#ifndef GDT_H
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#define GDT_H
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#include <stdint.h>
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#define GDT_NB_ENTRIES 3
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#define GDT_SIZE (GDT_NB_ENTRIES * sizeof(struct gdt_entry))
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#define KERNEL_CS_INDEX 1
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#define KERNEL_DS_INDEX 2
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struct gdt_entry
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{
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uint16_t limit_1 : 16;
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uint16_t base_1 : 16;
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uint8_t base_2 : 8;
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uint8_t accessed : 1;
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uint8_t rw : 1;
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uint8_t dc : 1;
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uint8_t ex : 1;
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uint8_t desc_type : 1;
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uint8_t desc_priv : 2;
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uint8_t present : 1;
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uint8_t limit_2 : 4;
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uint8_t available : 1;
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uint8_t l : 1;
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uint8_t db : 1;
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uint8_t granularity : 1;
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uint8_t base_3 : 8;
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} __attribute__ ((packed));
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struct gdt
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{
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struct gdt_entry entries[GDT_NB_ENTRIES];
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};
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struct gdt_r
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{
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uint16_t limit;
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uint32_t addr;
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} __attribute__ ((packed));
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struct segment_selector
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{
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uint8_t rpl : 2;
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uint8_t table_indicator : 1;
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uint16_t index : 13;
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} __attribute__ ((packed));
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void init_gdt();
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#endif /* !GDT_H */
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1
k/k.c
1
k/k.c
@ -30,6 +30,7 @@
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static void k_init(void)
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{
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init_serial();
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init_gdt();
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}
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void k_main(unsigned long magic, multiboot_info_t *info)
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@ -24,12 +24,12 @@ void init_serial(void)
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int write(const char *buf, size_t count)
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{
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int sent;
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size_t sent;
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for(sent = 0; sent < count; ++sent)
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{
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u8 line_status = inb(COM1 + 5);
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if (!line_status & EMPTY_TRANSMITTER)
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if (!(line_status & EMPTY_TRANSMITTER))
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break;
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outb(COM1, buf[sent]);
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}
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