current macro

[gerard4143]

Hi,

I'm running a 2.6.2.14-72.fc6 i586 kernel and I'm tring to figure out how it calculates the the current value in a kernel module. I took a objdump of a kernel module with the current marco and it produced this:

mov %fs:0x0, %eax
mov %eax, 0xc

and checking the %eax register I found it contained the current value but this is no help since I don't know what or how 0x0 (from %fs:0x0) is calculated

The only info I have on the current macro is from an old book and it states that the current value is arrived at by masking the %esp register with 0xffffe000 but an example of the values I get from my kernel module are:

current->0xc3608600
esp------>0xc2ef2e94

which doesn't compute...Thanks Gerard4143

[gerard4143]

Found the answer at this web page:

http://kernelnewbis.org/faq/current

essentially the struct task_struct is now included in a struct thread_info that resides at the bottom of the user kernel stack and my code for accessing it

struct thread_info *myti = 0;

void somefunc(void)
{
__asm__ __volatile__ 
(
"pushl %eax\n\t"
"movl %esp, %eax\n\t"
"andl $0xfffff000, %eax\n\t"
"movl %eax, myti\n\t"
"popl %eax\n\t"
)

printk("myti->task->pid->%d\n", myti->task->pid);
}