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arch/x86/paging.c

@@ -71,7 +71,7 @@ static inline void __native_flush_tlb_single(unsigned long addr)
     asm volatile("invlpg (%0)" ::"r"(addr) : "memory");
 }
 
-int pagingSetup(paddr_t upperKernelAddr)
+int pagingSetup(paddr_t lowerKernelAddr, paddr_t upperKernelAddr)
 {
     struct pdbr cr3;
 
@@ -85,7 +85,7 @@ int pagingSetup(paddr_t upperKernelAddr)
 
     // MMU not enabled for the moment. No need to use mirroring
     // Identity mapping up to upperKernelAddr
-    for (paddr_t i = 0; i < upperKernelAddr; i += PAGE_SIZE) {
+    for (paddr_t i = lowerKernelAddr; i < upperKernelAddr; i += PAGE_SIZE) {
         uint pdEntry = i >> (PD_SHIFT);
         uint ptEntry = (i >> PT_SHIFT) & PTE_MASK;
         struct pte *pt;

arch/x86/paging.h

@@ -5,7 +5,7 @@
 #define PAGING_MEM_READ (1U << 1)
 #define PAGING_MEM_WRITE (1U << 2)
 
-int pagingSetup(paddr_t upperKernelAddr);
+int pagingSetup(paddr_t lowerKernelAddr, paddr_t upperKernelAddr);
 
 int pageMap(vaddr_t vaddr, paddr_t paddr, int flags);
 int pageUnmap(vaddr_t vaddr);

core/allocArea.h

@@ -2,3 +2,5 @@
 #include "paging.h"
 
 void areaInit(void);
+vaddr_t areaAlloc(unsigned int nbPages);
+int areaFree(vaddr_t addr);

core/main.c

@@ -40,6 +40,7 @@ void kmain(unsigned long magic, unsigned long addr)
     unsigned long upperMemKB = 0;
     int memMapAvailable = 0;
     paddr_t lastUsedByMem;
+    paddr_t firstUsedByMem;
 
     VGASetup(BLACK, GREEN);
 
@@ -82,6 +83,7 @@ void kmain(unsigned long magic, unsigned long addr)
         if (CHECK_FLAG(mbi->flags, 6)) {
             memMapAvailable = 1;
         }
+        printf("Framebuffer from 0x%llx size (%dx%d) pitch %d bpp %d\n", mbi->framebuffer_addr, mbi->framebuffer_width, mbi->framebuffer_height, mbi->framebuffer_pitch, mbi->framebuffer_bpp);
     }
 
     if (upperMemKB == 0) {
@@ -90,7 +92,8 @@ void kmain(unsigned long magic, unsigned long addr)
     }
 
     printf("Setting up Mem\n");
-    memSetup(upperMemKB, &lastUsedByMem);
+
+    memSetup(upperMemKB, &firstUsedByMem, &lastUsedByMem);
 
     if (memMapAvailable) {
         multiboot_info_t *mbi             = (multiboot_info_t *)addr;
@@ -102,20 +105,27 @@ void kmain(unsigned long magic, unsigned long addr)
         for (uint i = 0; i < size; i++) {
             printf("   base_addr 0x%llx, length = 0x%llx, type = 0x%x\n", mmap[i].addr,
                    mmap[i].len, (uint32_t)mmap[i].type);
+            if(mmap[i].addr < 0x100000){ //Consider low memory taken (https://wiki.osdev.org/Detecting_Memory_(x86). For example by VGA
+                continue;
+            }
             memAddBank(max(mmap[i].addr, (multiboot_uint64_t)lastUsedByMem),
                        mmap[i].addr + mmap[i].len, mmap[i].type == MULTIBOOT_MEMORY_AVAILABLE);
         }
     } else {
         printf("Cannot get memory Mapping information, using default value\n");
-        memAddBank(0, lastUsedByMem, 0);
         memAddBank(lastUsedByMem, upperMemKB * 1024, 1);
     }
+    printf("%d pages taken by kernel(0x%x->0x%x))\n", (lastUsedByMem - firstUsedByMem)/PAGE_SIZE, firstUsedByMem, lastUsedByMem);
+    printf("with %d pages taken for memory management\n", (lastUsedByMem - (paddr_t)&__ld_kernel_end)/PAGE_SIZE);
 
 #ifdef RUN_TEST
     testPhymem();
 #endif
     printf("Setting up Pagination\n");
-    pagingSetup(lastUsedByMem);
+    pagingSetup(firstUsedByMem, lastUsedByMem);
+    for (paddr_t i = VGA_ADDR; i < VGA_ADDR + VGA_WIDTH * VGA_HEIGHT * sizeof(short) ; i += PAGE_SIZE) {
+        pageMap(i, i, PAGING_MEM_WRITE);
+    }
 
     printf("Setting up IRQ handlers\n");
     irqSetRoutine(IRQ_KEYBOARD, keyboard_handler);

core/mem.c

@@ -1,5 +1,5 @@
-#include "assert.h"
 #include "mem.h"
+#include "assert.h"
 #include "kernel.h"
 #include "klibc.h"
 #include "list.h"
@@ -13,7 +13,7 @@ paddr_t upperMem;
 
 static unsigned long allocatedPage = 0;
 
-int memSetup(paddr_t upperMemKB, paddr_t *lastMemUsedOut)
+int memSetup(paddr_t upperMemKB, paddr_t *firstUsed, paddr_t *lastMemUsedOut)
 {
     list_init(freePage);
     list_init(usedPage);
@@ -30,8 +30,13 @@ int memSetup(paddr_t upperMemKB, paddr_t *lastMemUsedOut)
     pageDescEnd     = (unsigned long)pageDesc + nbPage * sizeof(struct memDesc);
     *lastMemUsedOut = ALIGN(pageDescEnd, PAGE_SIZE);
     upperMem        = upperMemKB * 1024;
+    *firstUsed      = ALIGN_DOWN((paddr_t)&__ld_kernel_begin, PAGE_SIZE);
+
+    // Remove addr from 0 to PAGE_SIZE so we can return 0 for no page available
+    memAddBank(0, PAGE_SIZE, 0);
+
+    memAddBank(*lastMemUsedOut, *lastMemUsedOut, 0);
 
-    memAddBank(0, *lastMemUsedOut, 0);
     return 0;
 }
 
@@ -136,7 +141,7 @@ int unrefPhyPage(paddr_t addr)
     if (!mem) {
         return -1;
     }
-    assert(mem->ref >0);
+    assert(mem->ref > 0);
     mem->ref--;
     if (mem->ref == 0) {
         allocatedPage--;

core/mem.h

@@ -15,7 +15,7 @@ struct memDesc {
     struct memDesc *next, *prev;
 };
 
-int memSetup(paddr_t upperMem, paddr_t *lastUsed);
+int memSetup(paddr_t upperMem, paddr_t * firstUsed, paddr_t *lastUsed);
 int memAddBank(paddr_t bottomMem, paddr_t topMem, int isFree);
 paddr_t allocPhyPage(uint nbPage);
 int unrefPhyPage(paddr_t addr);