linux segment

[Fan Yang]

2012/10/28 Fan Yang <lljyangfan at gmail.com>

>
>
> 2012/10/27 Jun Hu <duanshuidao at hotmail.com>
>
>>   Can you post out your codes ?
>>
>>  *From:* Fan Yang <lljyangfan at gmail.com>
>> *Sent:* Wednesday, October 24, 2012 8:04 PM
>> *To:* kernelnewbies at 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 at 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.
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