when code segment, data segment or created when compiling a c program?

Question

I am trying to understand the compilation process of a C program. The pre-processed program was given to the compiler (to create obj file). The compiler will check for compilation errors. But somewhere I read that code segment, data segment will be created by the compiler and places the corresponding entries in to those segments. Is this correct?

How will the compiler create the segments in the memory? Since we haven't started running the program. Can anyone please let me know what are the exact things performed by the compiler?

Answer 1

This is quite simple.
So code segment is for instructions and data segment is for global and static variables.
It's obvious then, that in the end the compiler knows the size of both the code segment and data segment and this exactly the amount of memory required to load your program/library.

It's not actually memory allocation - this will happen at runtime.
But the point is that processor's instruction pointer should not get out of code segment. And this makes the length of code block quite important.

Answer 2

The compiler does not load the program. It only creates the executable file.

The text section and data section is created by the compiler and placed at the right places but only in the executable file. The executable is really just made up of descriptions and instructions to the runtime loader to tell it where to place code and data at run time.

Answer 3

As you mentioned, the text and data segments (and technically the BSS) are generated by the compiler. The text contains program code, the data contains global and static data. Those are all part of your binary image on disk.

The stack and the heap are not created by the compiler, but rather allocated at runtime -- they only exist in memory while the process is still alive.