OSDev.org

Code: Select all

#define PAGE_SHIFT	21  // for 2MB page using PAE
#define PAGE_SIZE	(1 << PAGE_SHIFT)

struct pde {
	uint32_t addr_lo;
	uint32_t addr_hi;
} __attribute__ ((packed));

static inline void paging_on(void *pdp)
{
	__asm__ __volatile__(
		/* Load the page table address */
		"movl	%0, %%cr3\n\t"
		/* Enable pae */
		"movl	%%cr4, %%eax\n\t"
		"orl	$0x00000020, %%eax\n\t"
		"movl	%%eax, %%cr4\n\t"
		/* Enable paging */
		"movl	%%cr0, %%eax\n\t"
		"orl	$0x80000000, %%eax\n\t"
		"movl	%%eax, %%cr0\n\t"
		:
		: "r" (pdp)
		: "ax"
		);
}


struct pde gPageDir[2048]     __attribute__ ((aligned(4096)));
struct pde gPageDirPtrTab[4]  __attribute__ ((aligned(4096)));
struct pde *pd                __attribute__ ((aligned(4096)));
struct pde *pdptr             __attribute__ ((aligned(4096)));

void PAE_InitPaging(uint32_t maxmem)
{
    uint32_t i, cr0;
    uint32_t pageflags = PF_GLOBAL | PF_PRESENT | PF_KERNELPAGE | PF_READWRITE;

    pd    = gPageDir;
    pdptr = gPageDirPtrTab;

    paging_off();

        // Point the page directory pointers at the page directories 
    pdptr[0].addr_lo = ((uint32_t)&pd[512*0])|1;
    pdptr[1].addr_lo = ((uint32_t)&pd[512*1])|1;
    pdptr[2].addr_lo = ((uint32_t)&pd[512*2])|1;
    pdptr[3].addr_lo = ((uint32_t)&pd[512*3])|1;

   //identity-map (maxmem == 512MB-1)
    for(i = 0; i < maxmem; i+= PAGE_SIZE)
    {
        printf("%d.. ",i/PAGE_SIZE);
        pd[i/PAGE_SIZE].addr_lo = i | pageflags;
        pd[i].addr_hi = 0;
        printf("0x%x \n",pd[i/PAGE_SIZE].addr_lo);
    }

    printf("..... turning on paging..\n");    // <= crashes immediately after this print

    paging_on(pdptr);

    printf("mapping done..\n");
    return;
}

Code: Select all

__inline void paging_on(void *pdp)
{
	__asm__ __volatile__(
/* Load the page table address */
            "movl	%0, %%cr3\n\t"
/* Enable pae */
            "movl	%%cr4, %%eax\n\t"
            "orl	$0x20, %%eax\n\t"
            "movl	%%eax, %%cr4\n\t"
            
/* Enable paging */
            "movl	%%cr0, %%eax\n\t"
            "orl	$0x80000000, %%eax\n\t"
            "movl	%%eax, %%cr0\n\t"
            "hlt    \n\t"               <====== system resets just before this point
            :
            : "r" (pdp)
            : "ax"
            );
}

Code: Select all

__inline void paging_on(void *pdp)
{
	__asm__ __volatile__(
/* Load the page table address */
            "movl	%0, %%cr3\n\t"
...