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noxos (docs): merged 'drivers/elf' docs from .wiki

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antifallobst 2023-03-15 21:08:02 +01:00
parent 9a2bef569b
commit 6f8721b376
8 changed files with 206 additions and 0 deletions
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content/projects/noxos/docs/codebase/drivers/elf.md Normal file
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---
title: "elf"
summary: "ELF executable parser"
---

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---
title: "elf"
---

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---
title: "elf.h"
summary: "The ELF-parsers' heart"
---
#### `elf_executable_T` - struct
This struct holds the parsed data of an ELF executable.
| Name | Type | Description |
|--------------|-------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------|
| header | [elf_header_T](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/header.h/#elf_header_t---struct) | The header of the elf file |
| num_symbols | uint64_t | The size of _symbols_ |
| symbols | symbol_T* | An array containing all symbols of the elf file |
| num_mappings | uint64_t | The size of _mappings_ |
| mappings | [elf_mapping_T](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/mapping.h/#elf_mapping_t---struct)* | An array containing the mappings needed to load the elf file |
| string_table | void* | A copy of the elf files `.strtab` section, all strings are referenced here to have them available even if the elf file is closed |
#### `elf_executable_temp_T` - struct
This struct is used while generating an [elf_executable_T](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/elf.h/#elf_executable_t---struct).
It holds parse-time information about the elf file.
| Name | Type | Description |
|-----------------------------|---------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------|
| executable | [elf_executable_T](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/elf.h/#elf_executable_t---struct)* | A pointer to the final [elf_executable_T](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/elf.h/#elf_executable_t---struct) |
| symbol_table | [elf_section_T](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/section.h/#elf_section_t---struct)* | A pointer to `.symtab` in _buffer_ |
| section_header_string_table | [elf_section_T](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/section.h/#elf_section_t---struct)* | A pointer to `.shstrtab` in _buffer_ |
| buffer | uint8_t* | The buffer where the executable is loaded from |
#### `elf_executable_create(buffer)` - function (elf_executable_T*)
Generates an [elf_executable_T](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/elf.h/#elf_executable_t---struct) from an elf file loaded to **_buffer_** and returns a pointer to it.
#### `elf_executable_destruct(executable)` - function (void)
Frees all memory allocated for [**_executable_**](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/elf.h/#elf_executable_t---struct).

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---
title: "header.h"
summary: "definitions needed to parse the ELF Header"
---
# `elf_target_architecture_E` - enum
Field in [header](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/header.h/#elf_header_t---struct): **identity[4]**
# `elf_endianness_E` - enum
Field in [header](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/header.h/#elf_header_t---struct): **identity[5]**
# `elf_sysabi_E` - enum
Field in [header](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/header.h/#elf_header_t---struct): **identity[7]**
# `elf_object_type_E` - enum
Field in [header](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/header.h/#elf_header_t---struct): **type**
# `elf_instruction_set_E` - enum
Field in [header](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/header.h/#elf_header_t---struct): **isa**
# `elf_header_T` - struct
| Name | Type | Description |
|----------------------------|-------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
| identity | uint8_t[16] | Information like the used endian and the SysABI is stored in here |
| type | uint16_t | The type of the elf file -> [elf_object_type_E](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/header.h/#elf_object_type_e---enum) |
| isa | uint16_t | The used instruction set -> [elf_instruction_set_E](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/header.h/#elf_instruction_set_e---enum) |
| version | uint32_t | ELF version |
| address_entry_point | uint64_t | The start point for program execution |
| offset_program_header | uint64_t | The position of the program header array in the file |
| offset_section_header | uint64_t | The position of the section header array in the file |
| flags | uint32_t | Architecture dependent, can be ignored |
| len_header | uint16_t | The size of this header |
| len_program_header_entry | uint16_t | The size of one program header |
| num_program_header_entries | uint16_t | The amount of program headers |
| len_section_header_entry | uint16_t | The size of one section header |
| num_section_header_entries | uint16_t | The amount of section headers |
| string_section_index | uint16_t | The section header index of the `.shstrtab` section |
# `g_elf_target_architecture_strings` - global variable
An array of strings matching [elf_target_architecture_E](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/header.h/#elf_target_architecture_e---enum).
# `g_elf_endianness_strings` - global variable
An array of strings matching [elf_endianess_E](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/header.h/#elf_endianess_e---enum).
# `g_elf_sysabi_strings` - global variable
An array of strings matching [elf_sysabi_E](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/header.h/#elf_sysabi_e---enum).
# `g_elf_object_type_strings` - global variable
An array of strings matching [elf_object_type_E](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/header.h/#elf_object_type_e---enum).
# `g_elf_instruction_set_strings` - global variable
An array of strings matching [elf_instruction_set_E](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/header.h/#elf_instruction_set_e---enum).

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---
title: "mapping.h"
summary: "handles the memory mappings that an ELF file can request"
---
# `elf_mapping_T` - struct
A mapping describes an area of memory,
that should be copied from the elf file into the RAM and how/where it should be mapped.
| Name | Type | Description |
|----------------|----------|------------------------------------------------------------------------------------------------------------------|
| offset_file | uint64_t | The mappings' start in the elf file |
| offset_virtual | uint64_t | The mappings' start in memory |
| length_file | uint64_t | The mappings' size in the elf file |
| length_virtual | uint64_t | The mappings' size in memory, if this is bigger than _length_file_ the remaining space will be filled with zeros |
# `elf_mappings_apply(mappings, num_mappings, buffer, base, page_map)` - function (void)
Maps all **_mappings_** into **_page_map_** and copies the related data from **_buffer_** (elf file) to the mapped memory.
**_base_** specifies where the mappings should start in the virtual address space.

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---
title: "section.h"
summary: "definitions needed to parse the elf section headers"
---
# `elf_section_type_E` - enum
- **Null** - These sections can be ignored
- **Program Data** - These link to segments, if I remember right
- **Symbol Table** - Here are all the executables' symbols stored
- **String Table** - Here are all strings stored
- **RelocationA** - Contains relocation information
- **Hash** - Symbol Table hash table
- **Dynamic Link** - This provides information for the dynamic linker
- **Note** - notes that were created by the compiler / toolchain
- **Nobits** - Nulled data like `.bss`
# `elf_section_T` - struct
| Name | Type | Description |
|-----------------|----------|-----------------------------------------------------------------------------------------------------------------------------------------------------|
| name_offset | uint32_t | The offset of the sections name in `.shstrtab` |
| type | uint32_t | The type of the section -> [elf_section_type_E](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/section.h/#elf_section_type_e---enum) |
| flags | uint64_t | Sections attribute flags |
| virtual_address | uint64_t | The address where the section should be mapped to (if it's not 0) |
| offset | uint64_t | The sections offset in the file |
| length | uint64_t | The size of the section |
| link | uint32_t | Type specific link to another section |
| info | uint32_t | Type specific information |
| alignment | uint64_t | If the section is aligned, this value specifies the alignment |
| entry_size | uint64_t | The size of the sections entries |
# `g_elf_section_type_strings` - global variable
An array of strings matching [elf_section_type_E](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/section.h/#elf_section_type_e---enum).

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---
title: "segment.h"
summary: "definitions needed to parse the elf program/segment headers"
---
# `elf_segment_type_E` - enum
- **Null** - Unused segment
- **Load** - Segment that should be included into mappings
- **Dynamic** - Segments of this type contain dynamic linking information
- **Interpreter** - This holds a path to an interpreter
- **Note** - These segments hold notes by the compiler / toolchain
- **Program Header Table** - This points to the table that is holding the segment headers
- **TLS** - This holds a Thread Local Storage template
# `elf_segment_T` - struct
| Name | Type | Description |
|------------------|----------|-----------------------------------------------------------------------------------------------------------------------------------------------|
| type | uint32_t | The segments type -> [elf_segment_type_E](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/segment.h/#elf_segment_type_e---enum) |
| flags | uint32_t | The segments flags (Read / Write / Execute) |
| offset | uint64_t | The segments position in the elf file |
| address_virtual | uint64_t | Where the segment should be mapped in the virtual address space |
| address_physical | uint64_t | Not used in the `System V` ABI |
| length_file | uint64_t | The segments size in the file |
| length_memory | uint64_t | The size of the area that should be mapped for the segment |
| align | uint64_t | The segments alignment (has to be a power of 2) |
# `g_elf_segment_type_strings` - global variable
An array of strings matching [elf_segment_type_E](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/segment.h/#elf_segment_type_e---enum).

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---
title: "symbol.h"
summary: "stuff needed to extract symbols from an ELFs `.symtab` section"
---
# `ELF_SYMBOL_TYPE(info)` - macro
Extracts the [elf_symbol_type_E](https://nerdcult.net/projects/noxos/docs/codebase/drivers/elf/symbol.h/#elf_symbol_type_e---enum) from the symbols info value.
# `elf_symbol_type_E` - enum
- **None** - Unspecified type
- **Object** - Data objects like variables, arrays, etc.
- **Func** - Function
- **Section** - Associated section
- **File** - The path to the source file associated with the object
- **Common** - Uninitialized common blocks
- **TLS** - Thread Local Storage
# `elf_symbol_T` - struct
| Name | Type | Description |
|-----------------------|-------------------------------------------------------------------|-------------|
| name_offset | The offset of the symbols name in `.strtab` | |
| info | Information about the symbol (type, bind) | |
| other | Information about the symbol (visibility) | |
| related_section_index | The index of the symbols related section | |
| value | Value, in most cases this is an address | |
| length | The size of the symbol (e.g. num bytes if the symbol is an array) | |