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typedef struct page
{
uint present : 1; // Page present in memory
uint rw : 1; // Read-only if clear, readwrite if set
uint user : 1; // Supervisor level only if clear
uint accessed : 1; // Has the page been accessed since last refresh?
uint dirty : 1; // Has the page been written to since last refresh?
uint unused : 7; // Amalgamation of unused and reserved bits
uint frame : 20; // Frame address (shifted right 12 bits)
} __packed page_t;
typedef struct{
page_t p[1024];
}__packed page_table_t;
typedef struct{
page_table_t *tabs[1024];
}__packed page_dir_t;
page_dir_t *page_dir;
page_table_t *kpage_tables;
void init_identity_paging(){
uint32_t frame;int i;
page_dir=k_AllocPage(1,OWNER_PAGEMAN);
memset(page_dir,0,sizeof(page_dir_t));
for(i=0;i<1024;i++){
page_dir->tabs[i]=0 ;
}
for(frame=0;frame<=(MEM_SIZE/0x1000);frame++){
mmap_to(frame,frame,1,1,1);
}
stopints();
write_cr3(page_dir);
write_cr0(read_cr0()|0x80000000); //set paging bit.
kput_hex(*(uint32_t*) &page_dir->tabs[0]);
kputs("\n");
startints();
}
void mmap_to(uint32_t src_page,uint32_t trg_page,int present,int rw,int user){
int i=1;
if(((uint32_t)page_dir->tabs[src_page/1024] & 0xFFFFF000)==0){
page_dir->tabs[src_page/1024]=(void*)
((uint32_t)k_AllocPage(1,OWNER_PAGEMAN) | 7);
for(i=0;i<1024;i++){
page_dir->tabs[src_page/1024]->p[i].present=0;
page_dir->tabs[src_page/1024]->p[i].rw=0;
page_dir->tabs[src_page/1024]->p[i].user=0;
page_dir->tabs[src_page/1024]->p[i].frame=0;
}
}
page_dir->tabs[src_page/1024]->p[src_page%1024].present=present;
page_dir->tabs[src_page/1024]->p[src_page%1024].rw=rw;
page_dir->tabs[src_page/1024]->p[src_page%1024].user=user;
page_dir->tabs[src_page/1024]->p[src_page%1024].frame=trg_page;
}
In my code, basically it assigns all page directory entries to 0. Then it starts to identity map. With the identity map, if the page directory entry is zero, then it allocates a physical page, assigns it to it, and then ORs that with 7(user/RW/present) and then assigns all of the page entires in the table to zero. Then, it will map the src_page to the trg_page.. pretty simply..
Whenever I enable paging in CR0 though, it triple-faults. does anyone see any immediate error with my code?
Also, the AllocPage function does what it says.. it returns a page address. So it is automatically page aligned.
