ROSE/paging.c

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C
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#include "paging.h"
uint32_t page_directory[1024] __attribute__((aligned(4096)));
uint32_t first_page_table[1024] __attribute__((aligned(4096))); // 0x00000000 - 0x00400000
uint32_t second_page_table[1024] __attribute__((aligned(4096))); // 0x00400000 - 0x00800000
void enable_paging() {
asm(
"mov %%eax, %%cr3\n"
"mov %%cr0, %%eax\n"
"or $0x80000001, %%eax\n"
"mov %%eax, %%cr0\n"
::"a"(page_directory));
}
void init_paging() {
for (int i = 0; i < 1024; i++)
// Supervisor, R/W, Not Present
page_directory[i] = 2;
// First Page Table
// First MB: Real Mode
{
int i;
// Up to 0xC0000
// TODO make some areas here Read Only
for (i = 0;i < 16*0xC; i++)
// User, R/W, Present
first_page_table[i] = (i * 0x1000) |4|2|1;
// Remainder of first MB BIOS Area (writable?)
for (;i < 256; i++)
// User, R/W, Present
first_page_table[i] = (i * 0x1000) |4|2|1;
}
// Next 3MB: Kernel
for (int i = 256; i < 1024; i++)
// Supervisor, R/W, Present
first_page_table[i] = (i * 0x1000) |2|1;
// Usermode Page Table
for (int i = 0; i < 1024; i++)
// User, R/W, Present
second_page_table[i] = (i * 0x1000 + 0x400000) |4|2|1;
// User, R/W, Present
page_directory[0] = ((uintptr_t)first_page_table)|4|2|1;
page_directory[1] = ((uintptr_t)second_page_table)|4|2|1;
enable_paging();
}