Monthly Archives: February 2016

TCC – struct CString for string process in compiler

struct CString is major struct for string process in TCC.
It also works some api such as cstr_reset(…),cstr_ccat(…).
Here is example on how to convert “char *” to s.data.

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  struct CString s;
 
  static char buf[STRING_MAX_SIZE + 1];
 
  char *p = "Test";
  char *p1 = p;
  char *p2 = p; 
 
  cstr_reset(&s);
 
  for(;;){
    if(*p2 != '\0')
      {
        p2++;
      }
    else
      break;
  }
 
  s.data = buf;  
 
  while (p1 < p2) {
    cstr_ccat(&s, *p1);
    p1++;
  }
 
  printf("%s",(char *)s.data);

Linux Kernel – start_kernel in main.c and task_struct for process management

Linux start with start_kernel function in main.c. It has lots of function, such mm_init for kernel memory allocators. Let’s start with some very basic components firstly.

task_struct is an basic and important struct for process.
It is defined in “include/linux/sched.h”

One process will be linked with others, for example, parent process and child process are linked together.

each member of task_struct is very critical and it is better to go though all of them to understand its better.

Check the definition of task_struct, you could print more information you want,

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#include <linux/module.h>
#include <linux/kernel.h> /* printk() */
#include <linux/errno.h>   /* error codes */
#include <linux/sched.h>
 
 
MODULE_LICENSE("Dual BSD/GPL");
 
/* Declaration of functions */
void device_exit(void);
int device_init(void);
 
/* Declaration of the init and exit routines */
module_init(device_init);
module_exit(device_exit);
 
int device_init(void)
{
    struct task_struct *task = current; // getting global current pointer
    printk(KERN_NOTICE "assignment: current process: %s, PID: %d", task->comm, task->pid);
    do
    {
        task = task->parent;
        printk(KERN_NOTICE "assignment: parent process: %s, PID: %d", task->comm, task->pid);
    } while (task->pid != 0);
    return 0;
}
 
void device_exit(void) {
  printk(KERN_NOTICE "assignment: exiting module");
}

Screenshot from 2016-02-12 01:39:43