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#include <stdint.h>
#include <cpuid.h>
#define PG_PRESENT 0x0000'0000'0000'0001
#define PG_READ_WRITE 0x0000'0000'0000'0002
#define PG_USER_SUPERVISE 0x0000'0000'0000'0004
#define PG_WRITE_THROUGH 0x0000'0000'0000'0008
#define PG_CACHE_DISABLE 0x0000'0000'0000'0010
#define PG_ACCESSED 0x0000'0000'0000'0020
#define PG_EXECUTE_DISABLE 0x8000'0000'0000'0000
#define F_PRESENT 0b1
#define F_WRITEABLE 0b10
#define F_UNPRIVILEGED 0b100
#define F_WRITETHROUGH 0b1000
#define F_CACHEDISABLE 0b10000
#define F_ACCESSED 0b100000
#define F_DIRTY 0b1000000
#define F_MEGABYTE 0b10000000
#define F_GLOBAL 0b100000000
// PAGE MAP LEVEL 4 ENTRY
struct pml4e {
uint64_t flags : 6;
uint64_t _reserved : 6;
uint64_t address : 40;
uint64_t _reserved_2 : 11;
uint64_t execute_disable : 1;
};
// PAGE DIRECTORY POINTER TABLE ENTRY
struct pdpte {
uint64_t flags : 6;
uint64_t _reserved : 1;
uint64_t page_size : 1;
uint64_t _reserved_2 : 2;
uint64_t address : 40;
uint64_t _reserved_3 : 11;
uint64_t execute_disable : 1;
};
// PAGE DIRECTORY ENTRY
struct pde {
uint64_t flags : 6;
uint64_t _reserved : 1;
uint64_t page_size : 1;
uint64_t _reserved_2 : 2;
uint64_t address : 40;
uint64_t _reserved_3 : 11;
uint64_t execute_disable : 1;
};
// PAGE TABLE ENTRY
struct pte {
uint64_t flags : 9;
uint64_t _reserved : 3;
uint64_t address : 40;
uint64_t _reserved_2 : 7;
uint64_t protection_key : 4;
uint64_t execute_disable : 1;
};
struct pml4e pml4[512];
struct pdpte pdpt[512];
struct pde pd[512];
struct pte pt[512];
static int get_maxphysaddr() {
uint32_t eax, ebx, ecx, edx;
__cpuid(0x80000008, eax, ebx, ecx, edx);
return eax & 0xFF;
}
// entry point for amd64
void* amd64_shim(void *boot_info) {
for (int i = 0; i < 512; i++) {
pml4[i].flags = 0;
}
for (int i = 0; i < 512; i++) {
pdpt[i].flags = 0;
}
for (int i = 0; i < 512; i++) {
pd[i].flags = 0;
}
pml4[0].flags = F_PRESENT | F_WRITEABLE;
pml4[0].address = (uint64_t)&pdpt;
pdpt[0].flags = F_PRESENT | F_WRITEABLE;
pdpt[0].address = (uint64_t)&pd;
pd[0].flags = F_PRESENT | F_WRITEABLE;
pd[0].address = (uint64_t)&pt;
for (int i = 0; i < 512; i++) {
pt[i].flags = F_PRESENT | F_WRITEABLE;
pt[i].address = i * 4096;
}
}
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