As far as I understand memory management in the Linux kernel, in every process there is a mm_struct structure responsible for the address space. One important area of memory is the stack. This should be identified by the vm_area_struct memory region, and mm_struct itself has a pointer mm_struct-> stack_start, which is the address of the stack.
I came from the code below and I don’t understand why any of the start / end addresses of the memory area is not equal to the value mm_struct-> stack_start. Any help in understanding this would be greatly appreciated. Thanks
Some of the results of loading a compiled kernel module:
Vma number 14: starts at 0x7fff4bb68000, ends at 0x7fff4bb8a000 Vma number 15: starts at 0x7fff4bbffe000, Vma number 16: starts at 0x7fff4bbfe000, ends at 0x7fff4bbfe000, code 0x4008 = 0 segment 0 = 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0x600a94 Starting stack segment = 0x7fff4bb88420
You may find that the beginning of the stack segment (0x7fff4bb88420) refers to vma 14, but I don’t know that the addresses are different.
Source code of the kernel module:
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/mm.h>
static int pid_mem = 1;
static void print_mem(struct task_struct *task)
{
struct mm_struct *mm;
struct vm_area_struct *vma;
int count = 0;
mm = task->mm;
printk("\nThis mm_struct has %d vmas.\n", mm->map_count);
for (vma = mm->mmap ; vma ; vma = vma->vm_next) {
printk ("\nVma number %d: \n", ++count);
printk(" Starts at 0x%lx, Ends at 0x%lx\n",
vma->vm_start, vma->vm_end);
}
printk("\nCode Segment start = 0x%lx, end = 0x%lx \n"
"Data Segment start = 0x%lx, end = 0x%lx\n"
"Stack Segment start = 0x%lx\n",
mm->start_code, mm->end_code,
mm->start_data, mm->end_data,
mm->start_stack);
}
static int mm_exp_load(void){
struct task_struct *task;
printk("\nGot the process id to look up as %d.\n", pid_mem);
for_each_process(task) {
if ( task->pid == pid_mem) {
printk("%s[%d]\n", task->comm, task->pid);
print_mem(task);
}
}
return 0;
}
static void mm_exp_unload(void)
{
printk("\nPrint segment information module exiting.\n");
}
module_init(mm_exp_load);
module_exit(mm_exp_unload);
module_param(pid_mem, int, 0);
MODULE_AUTHOR ("Krishnakumar. R, rkrishnakumar@gmail.com");
MODULE_DESCRIPTION ("Print segment information");
MODULE_LICENSE("GPL");