mirror of
https://github.com/cowmonk/cowos.git
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73 lines
1.8 KiB
C
73 lines
1.8 KiB
C
#include <gdt.h>
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static GDTEntry descriptors[5];
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static GDTPtr gdtptr;
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void
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gdt_reload()
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{
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asm volatile("lgdt %0\n\t"
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"push $0x28\n\t"
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"lea 1f(%%rip), %%rax\n\t"
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"push %%rax\n\t"
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"lretq\n\t"
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"1:\n\t"
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"mov $0x30, %%eax\n\t"
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"mov %%eax, %%ds\n\t"
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"mov %%eax, %%es\n\t"
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"mov %%eax, %%fs\n\t"
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"mov %%eax, %%gs\n\t"
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"mov %%eax, %%ss\n\t"
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:
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: "m"(gdtptr)
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: "rax", "memory");
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}
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void
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initGDT()
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{
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/* null descriptor (0) */
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descriptors[0].limit = 0;
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descriptors[0].base_low = 0;
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descriptors[0].base_mid = 0;
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descriptors[0].access = 0;
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descriptors[0].granularity = 0;
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descriptors[0].base_high = 0;
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/* kernel code 64 (40) */
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descriptors[1].limit = 0;
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descriptors[1].base_low = 0;
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descriptors[1].base_mid = 0;
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descriptors[1].access = 0b10011010;
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descriptors[1].granularity = 0b00100000;
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descriptors[1].base_high = 0;
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/* kernel data 64 (48) */
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descriptors[2].limit = 0;
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descriptors[2].base_low = 0;
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descriptors[2].base_mid = 0;
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descriptors[2].access = 0b10010010;
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descriptors[2].granularity = 0;
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descriptors[2].base_high = 0;
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// user code 64 (72)
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descriptors[3].limit = 0;
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descriptors[3].base_low = 0;
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descriptors[3].base_mid = 0;
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descriptors[3].access = 0b11111010;
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descriptors[3].granularity = 0b00100000;
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descriptors[3].base_high = 0;
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// user data 64. (80)
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descriptors[4].limit = 0;
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descriptors[4].base_low = 0;
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descriptors[4].base_mid = 0;
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descriptors[4].access = 0b11110010;
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descriptors[4].granularity = 0;
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descriptors[4].base_high = 0;
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gdtptr.limit = sizeof(descriptors) - 1;
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gdtptr.base = (uint64_t)&descriptors;
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gdt_reload();
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}
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