124 lines
2.3 KiB
C
124 lines
2.3 KiB
C
/*
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* vim:tabstop=4
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* vim:noexpandtab
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*/
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#include <system.h>
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static void write_tss(int32_t, uint16_t, uint32_t);
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tss_entry_t tss_entry;
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/*
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* Global Descriptor Table Entry
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*/
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struct gdt_entry {
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/* Limits */
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unsigned short limit_low;
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/* Segment address */
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unsigned short base_low;
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unsigned char base_middle;
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/* Access modes */
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unsigned char access;
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unsigned char granularity;
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unsigned char base_high;
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} __attribute__((packed));
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/*
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* GDT pointer
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*/
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struct gdt_ptr {
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unsigned short limit;
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unsigned int base;
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} __attribute__((packed));
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struct gdt_entry gdt[6];
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struct gdt_ptr gp;
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/*
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* (ASM) gdt_flush
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* Reloads the segment registers
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*/
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extern void gdt_flush();
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/*
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* gdt_set_gate
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* Set a GDT descriptor
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*/
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void
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gdt_set_gate(
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int num,
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unsigned long base,
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unsigned long limit,
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unsigned char access,
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unsigned char gran
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) {
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/* Base Address */
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gdt[num].base_low = (base & 0xFFFF);
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gdt[num].base_middle = (base >> 16) & 0xFF;
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gdt[num].base_high = (base >> 24) & 0xFF;
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/* Limits */
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gdt[num].limit_low = (limit & 0xFFFF);
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gdt[num].granularity = (limit >> 16) & 0X0F;
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/* Granularity */
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gdt[num].granularity |= (gran & 0xF0);
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/* Access flags */
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gdt[num].access = access;
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}
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/*
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* gdt_install
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* Install the kernel's GDTs
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*/
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void
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gdt_install() {
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/* GDT pointer and limits */
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gp.limit = (sizeof(struct gdt_entry) * 6) - 1;
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gp.base = (unsigned int)&gdt;
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/* NULL */
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gdt_set_gate(0, 0, 0, 0, 0);
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/* Code segment */
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gdt_set_gate(1, 0, 0xFFFFFFFF, 0x9A, 0xCF);
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/* Data segment */
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gdt_set_gate(2, 0, 0xFFFFFFFF, 0x92, 0xCF);
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/* User code */
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gdt_set_gate(3, 0, 0xFFFFFFFF, 0xFA, 0xCF);
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/* User data */
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gdt_set_gate(4, 0, 0xFFFFFFFF, 0xF2, 0xCF);
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write_tss(5, 0x10, 0x0);
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/* Go go go */
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gdt_flush();
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tss_flush();
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}
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static void
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write_tss(
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int32_t num,
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uint16_t ss0,
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uint32_t esp0
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) {
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uintptr_t base = (uintptr_t)&tss_entry;
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uintptr_t limit = base + sizeof(tss_entry);
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/* Add the TSS descriptor to the GDT */
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gdt_set_gate(num, base, limit, 0xE9, 0x00);
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memset(&tss_entry, 0x0, sizeof(tss_entry));
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tss_entry.ss0 = ss0;
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tss_entry.esp0 = esp0;
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tss_entry.cs = 0x0b;
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tss_entry.ss =
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tss_entry.ds =
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tss_entry.es =
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tss_entry.fs =
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tss_entry.gs = 0x13;
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}
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void
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set_kernel_stack(
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uintptr_t stack
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) {
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tss_entry.esp0 = stack;
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}
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