When I call the C system() function, is the location of the new program's main() stack frame similar to the original program's main() stack frame?

Question

I'm wondering if when I call the C system() function, the location of the new program's main() stack frame is similar to the original program's main() stack frame. Do anyone knows?

Below is "Program1" which calls system() to launch "Program2":

int main() {
   int i;
   system("Program2");
}

Here is "Program2":

int main() {
   int i;
}

I know that main() in "Program1" gets put on the stack, which means that the variable i will be on the stack. Let's say the address of this i in memory is 0x80000000.

Now, when system("Program2") is called and launches "Program2", the main() function of this program gets put on a stack too; however, in a different memory space (as far as I am aware), so the i for "Program2" will be in memory too, but in a different memory space from the i in "Program1".

Even though both i's will be in different memory spaces, will the address of i in "Program2" be similar or close to the address of i in "Program1" (0x80000000)?

For example, could it be something like 0x80000004 or close?

Answer 1

In modern operating systems, each process has its own address space, using virtual memory, so the address of i in Program1 could be the same as the address of i in Program2, without referring to the same area of RAM.

Furthermore, 64-bit OSes use address space randomisation, giving the stacks of various processes or running instances of the same executables different addresses.

Finally, the variables i in both processes may actually have no address at all as they could live in registers or be optimized out at compile time.

Merely printing the address with printf("%p\n", (void *)&i) will force the compiler to at least temporarily allocate some space on the stack for i.