2012/10/28 Fan Yang <lljyangfan@gmail.com>
2012/10/27 Jun Hu <duanshuidao@hotmail.com>
Can you post out your codes ?
*From:* Fan Yang <lljyangfan@gmail.com> *Sent:* Wednesday, October 24, 2012 8:04 PM *To:* kernelnewbies@kernelnewbies.org *Subject:* linux segment
Hi all: I print the cs ds and ss register in the user space, and it is same as the __USER_CS and __USER_DS which defined in kernel as 73 and 7b. In the kernel __KERNEL_CS and __KERNEL_DS defined as 60 and 68, but when I print this two value in my kernel module, I get 60 and 7b. Why ? It should be 60 and 68, shouldn't it?
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Hi Jun Hu There is my code which run at the user space:
1 #include<stdio.h> 2 main() 3 { 4 unsigned long cs, ds, ss, es, fs, gs; 5 asm volatile("movl %%CS,%0\n\t":"=r"(cs)); 6 asm volatile("movl %%DS,%0\n\t":"=r"(ds)); 7 asm volatile("movl %%SS,%0\n\t":"=r"(ss)); 8 asm volatile("movl %%ES,%0\n\t":"=r"(es));
9 asm volatile("movl %%FS,%0\n\t":"=r"(fs)); 10 asm volatile("movl %%GS,%0\n\t":"=r"(gs)); 11 printf ("**********************************\n"); 12 printf ("cs %lx\t%ld\n", cs, cs); 13 printf ("ds %lx\t%ld\n", ds, ds); 14 printf ("ss %lx\t%ld\n", ss, ss); 15 printf ("es %lx\t%ld\n", es, es); 16 printf ("fs %lx\t%ld\n", fs, fs); 17 printf ("gs %lx\t%ld\n", gs, gs); 18 printf ("**********************************\n"); 19 }
and the result of the progress in my machine is
********************************** cs 73 115 ds 7b 123 ss 7b 123 es 7b 123 fs 0 0 gs 33 51 **********************************
so, you can see the cs and ds register is 73 and 7b which are same as the kernel defined. And the code of the kernel module is
1 #include<linux/init.h>
2 #include<linux/kernel.h> 3 #include<linux/module.h> 4 5 static void __init print_init (void) 6 { 7 unsigned long cs, ds, ss, es, fs, gs,currenttime; 8 asm volatile("movl %%CS,%0\n\t":"=r"(cs)); 9 asm volatile("movl %%DS,%0\n\t":"=r"(ds)); 10 asm volatile("movl %%SS,%0\n\t":"=r"(ss)); 11 asm volatile("movl %%ES,%0\n\t":"=r"(es)); 12 asm volatile("movl %%FS,%0\n\t":"=r"(fs)); 13 asm volatile("movl %%GS,%0\n\t":"=r"(gs)); 14 printk ("**********************************\n"); 15 printk ("cs %lx\t%ld\n", cs, cs); 16 printk ("ds %lx\t%ld\n", ds, ds); 17 printk ("ss %lx\t%ld\n", ss, ss); 18 printk ("es %lx\t%ld\n", es, es); 19 printk ("fs %lx\t%ld\n", fs, fs); 20 printk ("gs %lx\t%ld\n", gs, gs); 21 printk ("**********************************\n"); 22 23 } 24 25 static void __exit print_exit (void) 26 { 27 unsigned long cs, ds, ss; 28 asm volatile("movl %%cs,%0\n\t":"=r"(cs)); 29 asm volatile("movl %%ds,%0\n\t":"=r"(ds)); 30 asm volatile("movl %%ss,%0\n\t":"=r"(ss)); 31 32 printk ("**********************************\n"); 33 printk ("cs %lx\t%ld\n", cs, cs); 34 printk ("ds %lx\t%ld\n", ds, ds); 35 printk ("ss %lx\t%ld\n", ss, ss); 36 printk ("**********************************\n"); 37 printk ("*****************bye***************\n"); 38 } 39 40 module_init (print_init); 41 module_exit (print_exit);
42 MODULE_LICENSE ("GPL");
the result of the running this module is
[root@shell--box kernel_mod]# dmesg -c ********************************** cs 60 96 ds 7b 123 ss 68 104 es 7b 123 fs d8 216 gs e0 224 **********************************
The cs and ds in the kernel space is 60 and 7b. But the kernel define the KERNEL_CS as 60 and the KERNEL_DS as 7b. Where am I wrong?
Thanks Fan
sorry, the kernel define the KERNEL_DS as 68, but I get 7b in my machine.