How can C allocate memory without an OS? (Cases where OS is written in C)

Question

I am following a course where we are writing an OS on a microcontroller.

The OS is written in C and the instructor initializes stack spaces for each thread in the following way.

int32_t TCB_STACK[NUM_OF_THREADS][STACK_SIZE];

How can the memory be allocated if there isn't any OS already running to service this in the first place? Am I missing something?

Answer 1

You don't have to "allocate" anything as such on a bare metal system, you have full access to all of the physical memory and there's no one else to share it with.

On such a system those arrays end up in statically allocated RAM memory known as .bss . Where .bss is located and how large it is, is determined by the linker script. The linker script decides which parts of the memory to reserve for what. Stack, .bss , .data and so on. Similarly the flash memory for the actual program may be divided in several parts.