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noxos (docs): merged 'mm/heap.h' and 'mm/region.h' docs from .wiki

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antifallobst 2023-03-16 00:02:09 +01:00
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content/projects/noxos/docs/codebase/mm/heap.h.md Normal file
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---
title: "heap.h"
summary: "dynamic memory allocator"
---
#### `heap_segment_T` - struct
This header lies in memory, directly before the accessible buffer of the related segment.
| Name | Type | Description |
|-------|---------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------|
| magic | uint32_t | An out of bounds memory write would override this, what would indicate a heap corruption |
| size | uint64_t | The size of the segment |
| free | bool | If this is set, the segment is reclaimable |
| next | [heap_segment_T](https://nerdcult.net/projects/noxos/docs/codebase/mm/heap.h/#heap_segment_t---struct)* | The next segment in the heap |
| prev | [heap_segment_T](https://nerdcult.net/projects/noxos/docs/codebase/mm/heap.h/#heap_segment_t---struct)* | The previous segment in the heap |
#### `heap_T` - struct
| Name | Type | Description |
|--------------|---------------------------------------------------------------------------------------------------------|-------------------------------------------------------------|
| start | void* | The start of the heaps segment pool |
| end | void* | The current end of the heaps segment pool (growing upwards) |
| last_segment | [heap_segment_T](https://nerdcult.net/projects/noxos/docs/codebase/mm/heap.h/#heap_segment_t---struct)* | The current last segment in the heaps segment pool |
#### `heap_init(heap*, base)` - function (void)
Initializes **_heap_** at **_base_** (virtual address).
It will automatically map some page frames to that address.
#### `heap_memory_allocate(heap*, size)` - function (void)
Returns a pointer to a free usable memory location, that has at least the given **_size_**.
It will return `NULL` and log an error, if the heap is corrupted.
Because this function iterates over the entire heap to find a free segment, it is kinda slow.
#### `heap_memory_free(heap*, address)` - function (void)
Frees a with [heap_memory_allocate](https://nerdcult.net/projects/noxos/docs/codebase/mm/heap.h/#heap_memory_allocateheap-size---function-void)* created heap segment, and makes it usable again.
Does nothing, if the address doesn't point to a valid heap segment.
#### `heap_dump_segments(heap*)` - function (void)
Logs a complete list, of all heap segments.
Useful, when debugging / testing the heap.
#### `heap_destruct(heap*)` - function (void)
Invalidates all segments of a heap, frees all used page frames and unmaps them.

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---
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).