Hi, In arm linux, kernel stack is 8KB(two consecutive pages). struct pt_regs lie at the top of the stack and thread_info lie at the bottom of the stack. In arch/arm/include/asm/processor.h #define task_pt_regs(p) \ ((struct pt_regs *)(THREAD_START_SP + task_stack_page(p)) - 1) In arch/arm/include/asm/threadinfo.h #define THREAD_START_SP (THREAD_SIZE - 8) Why are 8 bytes reserved at the top ? Also, seeing similar thing in arch/arm/include/asm/ptrace.h #define current_pt_regs(void) ({ (struct pt_regs *) \ ((current_stack_pointer | (THREAD_SIZE - 1)) - 7) - 1; \ }) (current_stack_pointer | (THREAD_SIZE - 1) It will get the top of stack and the we are subtracting 7 from it ? Why are these bytes reserved ? Thanks & Regards