well, the address in IDT is physical, in the below URL u can read about the problem experienced by a guy who used the IDTR contents directly without mapping it and the proposed solution. http://seclists.org/lists/linux-kernel/2002/Apr/0921.html For that matter even the CR3 register which points to the page directory holds the physical address and not the virtual address of the Page Directory. Linux uses the term 'swapper_pg_dir' to refer to this page directory and this is a virtual address, but when it wants to store the address of the page directory in to CR3 register it does as below " kernel/process.c:314: asm volatile("movl %0,%%cr3": :"r" (__pa(swapper_pg_dir)));" Avoids the overhead for the processor to convert the virtual address to physical address for referrring these tables gop -----Original Message----- From: Dhiman, Gaurav [mailto:Gaurav.Dhiman@xxxxxx] Sent: Friday, October 01, 2004 10:31 AM To: Thekkedath, Gopakumar; Ashish Mishra Cc: Kenel Newbies Subject: RE: Seek Help !!! (about getting a pointer to sys_call_table) NO, IDTR contains the virtual address of IDT, it also contains the length of IDT in number of bytes. Cheers !! Gaurav -----Original Message----- From: Thekkedath, Gopakumar [mailto:Gopakumar.Thekkedath@xxxxxxx] Sent: Friday, October 01, 2004 9:32 AM To: Dhiman, Gaurav; Ashish Mishra Cc: Kenel Newbies Subject: RE: Seek Help !!! (about getting a pointer to sys_call_table) >1. - get the pointer to IDT (Interrupt Descriptor Table), using SIDT >assembly instruction. This instruction will store the value of IDTR >register of processor, which actually is a pointer to IDT in kernel. >2. - Once you get the pointer to IDT, get to the 128th entry of IDT by >multiplying 128 with 8 (as each entry in IDT is of 8 bytes) and adding >that to the IDT pointer, which we got in first step. This is a pointer >to the system gate through with system calls enter kernel mode. Just a thought, the IDTR holds the physical address of the IDT in memory right? so to use that in the kernel, u may have to convert it to virtual address. gop -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
