---
title: "region.h"
summary: "virtual memory space layout"
---

The first 4 digits of an address can be ignored, they are also ignored by the MMU,
but for clarity / readability reasons they are `FFFF` in the kernel space.
See _General Concepts / Memory Layout_(todo: add reference) and _General Concepts / Process Memory Isolation_(todo: add reference) for more details.

| Name                             | Start              | Description                                       |
|----------------------------------|--------------------|---------------------------------------------------|
| `MEM_REGION_PROCESS`             | 0x0000000000000000 | This is the start of the process space            |
| `MEM_REGION_PROCESS_EXEC`        | 0x0000010000000000 | Every processes' executable will be mapped here   |
| `MEM_REGION_PROCESS_THREAD_BASE` | 0x0000010100000000 | The start of the _Thread Data_ regions            |
| `MEM_REGION_KERNEL`              | 0xFFFF800000000000 | This is the start of the kernel space             |
| `MEM_REGION_KERNEL_STACK_DUMMY`  | 0xFFFFF00000000000 | This area is used when preparing a threads' stack |
| `MEM_REGION_KERNEL_HEAP`         | 0xFFFFF80000000000 | The kernels' heap begins here                     |
| `MEM_REGION_KERNEL_THREAD_BASE`  | 0xFFFFFF0000000000 | The kernel processes' _Thread Data_ regions       |
| `MEM_REGION_KERNELEXEC`          | 0xFFFFFFFF80000000 | The kernel executable is mapped here              |

# `MEM_REGION_THREAD_OFFSET` - macro
This time the threads id specifies its offset in its processes' _Thread Data_ region.

# `KERNEL_START_ADDRESS` - macro
Returns the address of [_kernel_start](https://nerdcult.net/projects/noxos/docs/codebase/mm/region.h/#_kernel_start---global-variable).

# `KERNEL_END_ADDRESS` - macro
Returns the address of [_kernel_end](https://nerdcult.net/projects/noxos/docs/codebase/mm/region.h/#_kernel_end---global-variable).

# `_kernel_start` - global variable
This symbol is inserted by the linker at the beginning of the kernel.
To access its value use [KERNEL_START_ADDRESS](https://nerdcult.net/projects/noxos/docs/codebase/mm/region.h/#kernel_start_address---macro).

# `_kernel_end` - global variable
This symbol is inserted by the linker at the end of the kernel.
To access its value use [KERNEL_END_ADDRESS](https://nerdcult.net/projects/noxos/docs/codebase/mm/region.h/#kernel_end_address---macro).