> I have very much confusion about the difference > between user space and kernel space. > I mean as far as I know when a programme is executed > i.e simple C prog. it contains three sections in > memory such as gobal, data and text section. > There is somthing called user stack and kernel stack > there. whenever a process get the turn to be executed > by the scedular its stack contain is copied to the > kernel stack(correct me if I'm goin wrong.) The user-space stack never touches the kernel-space stack, see below for further explanation. > Now when we say we execute a system call it jumps to > the kernel level. Now if we see the it by kernel stack > when the stack frame is executed on which the call to > system call is made, how come it jumps to kernel > mode.. There are two stacks, one for the user-space space part of the process and one for the kernel part. You cannot arbitrarily modify the kernel stack of a process and there's no reason you should have to. When your process running in user-space for example does a system call the kernel will start using the kernel stack for the process. When passing data between user-space and kernel the hardware registers are used (at least for x86, but i think quite much everyone does similar). > Now related to this, we say kernel code doesnt have > address space, now what does that mean..I mean to > execute the code it has to have some memory on which > to be reside and get executed.. There is an address space, it's just different from the address space normally meant as referring to user-space. -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
