noxos (docs): merged 'mm/heap.h' and 'mm/region.h' docs from .wiki
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title: "heap.h"
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summary: "dynamic memory allocator"
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---
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#### `heap_segment_T` - struct
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This header lies in memory, directly before the accessible buffer of the related segment.
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| Name | Type | Description |
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|-------|---------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------|
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| magic | uint32_t | An out of bounds memory write would override this, what would indicate a heap corruption |
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| size | uint64_t | The size of the segment |
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| free | bool | If this is set, the segment is reclaimable |
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| next | [heap_segment_T](https://nerdcult.net/projects/noxos/docs/codebase/mm/heap.h/#heap_segment_t---struct)* | The next segment in the heap |
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| prev | [heap_segment_T](https://nerdcult.net/projects/noxos/docs/codebase/mm/heap.h/#heap_segment_t---struct)* | The previous segment in the heap |
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#### `heap_T` - struct
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| Name | Type | Description |
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|--------------|---------------------------------------------------------------------------------------------------------|-------------------------------------------------------------|
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| start | void* | The start of the heaps segment pool |
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| end | void* | The current end of the heaps segment pool (growing upwards) |
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| 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 |
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#### `heap_init(heap*, base)` - function (void)
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Initializes **_heap_** at **_base_** (virtual address).
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It will automatically map some page frames to that address.
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#### `heap_memory_allocate(heap*, size)` - function (void)
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Returns a pointer to a free usable memory location, that has at least the given **_size_**.
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It will return `NULL` and log an error, if the heap is corrupted.
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Because this function iterates over the entire heap to find a free segment, it is kinda slow.
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#### `heap_memory_free(heap*, address)` - function (void)
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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.
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Does nothing, if the address doesn't point to a valid heap segment.
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#### `heap_dump_segments(heap*)` - function (void)
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Logs a complete list, of all heap segments.
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Useful, when debugging / testing the heap.
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#### `heap_destruct(heap*)` - function (void)
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Invalidates all segments of a heap, frees all used page frames and unmaps them.
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---
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title: "region.h"
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summary: "virtual memory space layout"
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---
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The first 4 digits of an address can be ignored, they are also ignored by the MMU,
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but for clarity / readability reasons they are `FFFF` in the kernel space.
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See _General Concepts / Memory Layout_(todo: add reference) and _General Concepts / Process Memory Isolation_(todo: add reference) for more details.
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| Name | Start | Description |
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|----------------------------------|--------------------|---------------------------------------------------|
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| `MEM_REGION_PROCESS` | 0x0000000000000000 | This is the start of the process space |
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| `MEM_REGION_PROCESS_EXEC` | 0x0000010000000000 | Every processes' executable will be mapped here |
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| `MEM_REGION_PROCESS_THREAD_BASE` | 0x0000010100000000 | The start of the _Thread Data_ regions |
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| `MEM_REGION_KERNEL` | 0xFFFF800000000000 | This is the start of the kernel space |
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| `MEM_REGION_KERNEL_STACK_DUMMY` | 0xFFFFF00000000000 | This area is used when preparing a threads' stack |
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| `MEM_REGION_KERNEL_HEAP` | 0xFFFFF80000000000 | The kernels' heap begins here |
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| `MEM_REGION_KERNEL_THREAD_BASE` | 0xFFFFFF0000000000 | The kernel processes' _Thread Data_ regions |
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| `MEM_REGION_KERNELEXEC` | 0xFFFFFFFF80000000 | The kernel executable is mapped here |
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#### `MEM_REGION_THREAD_OFFSET` - macro
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This time the threads id specifies its offset in its processes' _Thread Data_ region.
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#### `KERNEL_START_ADDRESS` - macro
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Returns the address of [_kernel_start](https://nerdcult.net/projects/noxos/docs/codebase/mm/region.h/#_kernel_start---global-variable).
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#### `KERNEL_END_ADDRESS` - macro
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Returns the address of [_kernel_end](https://nerdcult.net/projects/noxos/docs/codebase/mm/region.h/#_kernel_end---global-variable).
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#### `_kernel_start` - global variable
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This symbol is inserted by the linker at the beginning of the kernel.
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To access its value use [KERNEL_START_ADDRESS](https://nerdcult.net/projects/noxos/docs/codebase/mm/region.h/#kernel_start_address---macro).
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#### `_kernel_end` - global variable
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This symbol is inserted by the linker at the end of the kernel.
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To access its value use [KERNEL_END_ADDRESS](https://nerdcult.net/projects/noxos/docs/codebase/mm/region.h/#kernel_end_address---macro).
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