c94252c3f2
GDT control is how I would like it to be but there are some issues, namely: 1. far jumping to flush the code segment crashes the whole os(not good) 2. Segment selectors seem fine apart from the code segment thing 3. some administrative issues regarding the structure of the project which is slowly making things painful
40 lines
1.2 KiB
C
40 lines
1.2 KiB
C
#include "gdt.h"
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// Congirures a given gdt entry base on the entry index given
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void gdt_configure_entry(u32 entry, u32 base, u32 limit, u8 access, u8 gran) {
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// base address
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gdt_entries[entry].low_base = (base & 0xffff);
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gdt_entries[entry].middle_base = (base >> 16) & 0xff;
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gdt_entries[entry].high_base = (base >> 24) & 0xff;
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// descriptor limits
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gdt_entries[entry].low_limit = (limit & 0xffff);
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gdt_entries[entry].granular = ((limit >> 16) & 0x0f);
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gdt_entries[entry].granular |= (gran & 0xf0);
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gdt_entries[entry].access = access;
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}
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// Configure the gdt pointer desribed in gdt.h as type GDT_PTR
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void gdt_configure() {
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// gdt_ptr configuration
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gdt_ptr.size = (sizeof(struct GDT_Entry) * NO_GDT_ENTRIES) - 1;
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// First entry is just the null descriptor and is left along overall
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gdt_configure_entry(0, 0, 0, 0, 0);
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// Second entry: code segment base adders
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// Base address: 0
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// limit: 4GB
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// Granularity: 4KB
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// 32-bit opcodes
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// Code segment selector
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gdt_configure_entry(1, 0, 0xffffffff, 0x9a, 0xcf);
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// Finally the data segment
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// All the same except the desriptor type specifies that its data
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gdt_configure_entry(2, 0, 0xffffffff, 0x92, 0xcf);
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// Load in the new changes to the gdt
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load_gdt();
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}
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