From 5a9a57177f730d1c00ab2b47f91e5ea2660a4f77 Mon Sep 17 00:00:00 2001
From: Loic Guegan <manzerbredes@mailbox.org>
Date: Tue, 13 Apr 2021 15:31:45 +0200
Subject: Enable .bss zeroing and improve paging

---
 src/core/paging.c | 98 +++++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 88 insertions(+), 10 deletions(-)

(limited to 'src/core/paging.c')

diff --git a/src/core/paging.c b/src/core/paging.c
index b1f462f..c32a3bc 100644
--- a/src/core/paging.c
+++ b/src/core/paging.c
@@ -1,21 +1,43 @@
 #include "paging.h"
+#include "libc/stdio.h"
+
+/// Use a bitmap to keep track of allocated pages
+char pages_status[PAGING_MAX_PAGES/8];
+/// Kernel page directory (ATTENTION need to be 4096)
+u32 k_pd[PAGING_MAX_DIR_ENTRY] __attribute__((aligned(4096)));
+/// Kernel page table
+u32 k_pt[PAGING_MAX_DIR_ENTRY][1024] __attribute__((aligned(4096)));
 
 void paging_enable(){
-    int *page_dir=(int*)PAGING_DIR_LOCATION;
-    int *page_table=(int*)PAGING_TABLE_LOCATION;
+    // Init pages status
+    for(int i=0;i<PAGING_MAX_PAGES/8;i++)
+        pages_status[i]=0;
 
     // Init page directory
-    for(int i=0;i<1024;i++)
-        page_dir[i]=0;
-    page_dir[0]=(int)page_table;
-    page_dir[0] |=7; // Permissions
+    for(int i=0;i<PAGING_MAX_DIR_ENTRY;i++){
+        k_pd[i]=0;
+    }
+    k_pd[0]=((int)&k_pt[0][0]);
+    k_pd[0]|=7; // Permissions
 
     // Init page table 0
     int addr_offset=0;
     for(int i=0;i<1024;i++){
-        page_table[i]=addr_offset;
-        page_table[i]|=7; // Permission
-        addr_offset+=4096; // 4Ko pages
+        k_pt[0][i]=addr_offset;
+        k_pt[0][i]|=7; // Permission
+        paging_set_usage(addr_offset,1); // Mark addr as used
+        addr_offset+=PAGING_PAGE_SIZE; // 4Ko pages
+    }
+
+    // Allow access to more ram
+    for(int i=1;i<PAGING_MAX_DIR_ENTRY;i++){
+        k_pd[i]=((int)&k_pt[i][0]);
+        k_pd[i]|=7; // Permissions
+        for(int j=0;j<1024;j++){
+            k_pt[i][j]=addr_offset;
+            k_pt[i][j]|=7; // Permission
+            addr_offset+=PAGING_PAGE_SIZE; // 4Ko pages
+        }
     }
 
     // Turns on paging
@@ -25,7 +47,63 @@ void paging_enable(){
         "movl %%cr0, %%eax    \n\t"
         "orl %1, %%eax        \n\t"
         "movl %%eax, %%cr0    \n\t" // Turn on paging
-        :: "i" (PAGING_DIR_LOCATION), "i" (PAGING_CR0_BIT)
+        :: "b" (k_pd), "i" (PAGING_CR0_BIT)
     );
+}
+void paging_set_usage(int addr,char state){
+    char bytes=pages_status[addr/PAGING_PAGE_SIZE/8];
+    char bit=addr/PAGING_PAGE_SIZE%8;
+    if(state=0)
+        pages_status[addr/PAGING_PAGE_SIZE/8]=~(1<<bit)&bytes;
+    else
+        pages_status[addr/PAGING_PAGE_SIZE/8]=(1<<bit)|bytes;
+}
+
+void paging_dump(int min,int max){
+    for(int i=0;i<(PAGING_MAX_PAGES/8);i++){
+        for(int j=0;j<8;j++){
+            char status=(pages_status[i]>>j)&0x1;
+            if((i*8+j)>=min){
+                if((i*8+j)<max || max<0)
+                    printi(status);
+            }
+        }
+    }
+}
+
+char* paging_allocate_next_page(){
+    for(int i=0;i<(PAGING_MAX_PAGES/8);i++){
+        char bytes=pages_status[i];
+        for(int j=0;j<8;j++){
+            char state=(bytes>>j)&1;
+            if(state!=1){
+                int page_id=i*8+j;
+                int page_addr=PAGING_PAGE_SIZE*page_id;
+                paging_set_usage(page_addr,1);
+                return((char*)page_addr);
+            }
+        }
+    }
+    print("Could not allocate anymore pages! Stopping...");
+    asm("hlt");
+}
 
+
+char *paging_allocate(int p){
+    int *page_dir=(int*)paging_allocate_next_page();
+    int *page_table;
+    int current_page_entry=0;
+    int current_dir_entry=0;
+    while(current_page_entry<p){
+        if(current_page_entry%1024 == 0){
+            current_dir_entry++;
+            page_table=(int*)paging_allocate_next_page();
+            page_dir[current_dir_entry]=(int)page_table;
+        }
+        int entry=current_page_entry%1024;
+        page_table[current_page_entry]=(int)paging_allocate_next_page();
+        current_page_entry++;
+        print("Jean\n");
+    }
+    print("end");
 }
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