55 lines
1.5 KiB
C
55 lines
1.5 KiB
C
#include "gdt.h"
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#include "libc.h"
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#include "str.h"
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inline uint16_t gdt_segment_selector(uint16_t index, uint16_t table_indicator, uint16_t priv_level)
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{
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return (index << 3)
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| ((table_indicator << 2) & 0b100)
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| ((priv_level << 0) & 0b011);
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}
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struct gdt_table_entry gdt_encode_entry(struct gdt_entry_content content)
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{
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if (content.limit > GDT_LIMIT_MAX)
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panic(str_attach("GDT cannot encode limits larger than " CSTR(GDT_LIMIT_MAX)));
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struct gdt_table_entry entry;
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entry.data[GDT_SDESC_LIMIT_0] = (content.limit >> 0) & 0xFF;
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entry.data[GDT_SDESC_LIMIT_1] = (content.limit >> 8) & 0xFF;
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entry.data[GDT_SDESC_LIMIT_2] = (content.limit >> 16) & 0xFF;
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entry.data[GDT_SDESC_BASE_0] = (content.base >> 0) & 0xFF;
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entry.data[GDT_SDESC_BASE_1] = (content.base >> 8) & 0xFF;
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entry.data[GDT_SDESC_BASE_2] = (content.base >> 16) & 0xFF;
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entry.data[GDT_SDESC_BASE_3] = (content.base >> 24) & 0xFF;
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entry.data[GDT_SDESC_ACCESSBYTE] = content.access_byte;
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entry.data[GDT_SDESC_FLAGS] |= (content.flags << 4);
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return entry;
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}
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void gdt_set(uint16_t size, const struct gdt_table_entry base[], uint32_t offset)
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{
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base += offset;
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/* the lgdt instruction requires a packed alignment */
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struct __attribute__((packed)) gdtr {
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uint16_t size;
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uint32_t base;
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} gdt = {
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.size = size,
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.base = (uint32_t)base,
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};
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__asm__ volatile (
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"lgdt %[gdt]"
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:
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: [gdt] "m"(gdt)
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);
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}
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