On Sunday 03 Apr 2011 2:22:19 am James Light wrote: > On Sat, Apr 02, 2011 at 11:18:19PM +0530, mindentropy wrote: > > On Saturday 02 Apr 2011 9:55:35 pm James Light wrote: > > > To put the physical address into cr3 later. > > > $swapper_pg_dir is not the PHYSICAL address of the PGD. > > > > Correct me if I am wrong but a mov $foo,%eax would move the address of > > foo variable to eax right? Or is there a macro somewhere where they are > > adding PAGE_OFFSET to the address so that the $swapper_pg_dir - > > __PAGE_OFFSET justifies? > > Right, but it uses the logical address of foo which n the case of > swapper_pg_dir must be converted to a > physical address. When paging is not enabled, linear addresses are > interpreted as physical addressess. > So it has to get this logical address > only one step farther into a linear address. > Can you please elaborate on what one step farther is? So why not use the swapper_pg_dir directly i.e. mov $swapper_pg_dir,cr0? In the absence of paging the segment:offset is the physical address isn't it? i.e. the $swapper_pg_dir should be equal to 0x10100 as per the code fragment below? I am having difficulty in understanding the addressing calculations here and not the code, >In linux2.1.66, the physical address is used directly. >Just for comparison: >------------------------------------------------------------------------------ >58/* >59 * Setup paging (the tables are already set up, just switch them on) >60 */ >611: >62 movl $0x101000,%eax >63 movl %eax,%cr3 /* set the page table pointer.. */ >64 movl %cr0,%eax >65 orl $0x80000000,%eax >66 movl %eax,%cr0 /* ..and set paging (PG) bit */ >67 jmp 1f /* flush the prefetch-queue */ >----------------------------------------------------------------------------- _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
