Memory allocation layout issues in C (64-bit)

Question

I wanted to understand how a "C" program runs and store the data in machine. So I looked into Memory Layout of C from here and I followed the same instructions in my machine which is 64-bit.

First when I wrote the program (main has only return 0;) and used the size command for the executable file: it showed a lot of difference in both text and data segments.

text    data    bss     dec     hex     filename
10648   2400    2640    15688   3d48    33.exe

But in the website mentioned above it showed:

text    data    bss     dec     hex     filename
960     248     8       1216    4c0     memory-layout

First Question: What are the factors (hardware/software) that are responsible for the memory allocation?. And what does dec in the layout refer to? /Question ends here

But first I ignored this and started declaring the variables (global and static) to see where they are being stored. And I was facing a problem in this phase.

for this code:

#include <stdio.h> 
int global;  
int main(void) {
    //static int x;
    return 0; 
} 

I got output as:

text    data    bss     dec     hex     filename
10648   2400    2656    15704   3d48    33.exe

That is because I declared (uninitialised) a global variable and that is why 16 bytes (int-64bit) of memory block has been added to the bss so it became 2656 from 2640 (first example) I understand this.

Q2: But when I add the static int x it is not adding the memory block to bss anymore. Is this expected?

text    data    bss     dec     hex     filename
10648   2400    2656    15704   3d48    33.exe 

Q3: And finally when I initialize the global variable with 20, data got incremented (expected) and dec also got incremented why?

text    data    bss     dec     hex     filename
10648   2416    2656    15720   3d48    33.exe

I know I asked many questions here, but I wanted to know exactly how this memory management works in C.

Arigato:)

Answer 1

What are the factors (Hardware/Software) that are responsible for the memory allocation?. And what does dec in the layout refer to

Your program is divided into many sections when it runs. stack contains the local variables. bss data contains the uninitalized global variables. initialized data contains the initialized global variables. text contains your text (code). dec is the sum of text, bss , data

But when i add the static int x it is not adding the memory block to bss anymore.is it expected?

Keep it uninitialized then it will add.

Before adding static variable:

   text    data     bss     dec     hex filename
   1099     544       8    1651     673 a.out

After adding static variable:

   text    data     bss     dec     hex filename
   1099     544      16    1659     67b a.out

And finally when i initialize the global variable with 20, data got incremented (expected) and dec also got incremented. Why?

Because dec is the sum of text, data , bss