Isn't the start address of the stack fixed in linux?

unsigned long find_start(void){
    __asm__("movq %rsp, %rax");
}
int main(){
    printf ("OX%x\n" , find_start()) ;
}

This is a further question of my previous one,

the output is different each time I run the programe.

isn't the start address of the stack fixed in linux?

The kernel version is 2.6.18-194.el5

Update from comments: I'm now tryi开发者_Go百科ng to do a hello world exploit,how to overcome this?Will the process created by execve be using the same stack start address as its parent process?

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Perhaps you're seeing the effect of address space layout randomization. It's a security feature, to make it harder to exploit stack or buffer overruns.

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See Pseudo-random stack pointer under Linux?

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How would that be possible on an operating system that supports multiple processes and multiple threads?

EDIT: I should mention what I brought up in the comments: Address Space Layout Randomization, a security feature that deliberately scrambles the address around.