question about get_user

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Hi, all,

I have a problem with get_user() macro. What I did is as follows:

I run the following program

int main()
{
       int a = 20;
       printf("address of a: %p", &a);
       sleep(200);
       return 0;
}

When the program runs, it outputs the address of a, say, 0xbff91914.

Then I pass this address to a module running in Kernel Mode that
retrieves the contents at this address (at the time when I did this, I
also made sure the process didn't terminate, because I put it to sleep
for 200 seconds... ):

The address is firstly sent as a string, and I cast them into pointer type.

int * ptr = (int*)simple_strtol(buffer, NULL,16);
printk("address: %p",ptr); // I use this line to make sure the cast is
correct. When running, it does output bff91914
int val = 0;
int res;
res= get_user(val, (int*) ptr);

However, res is always not 0, meaning that get_user returns error. I
am wondering what is the problem....

Thank you!!

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