ELF type, struct, macro definitions

.clang-format

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+AlignConsecutiveDeclarations:
+  Enabled: false
+  AcrossComments: true
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doc/15_elf_files.md

@@ -1,11 +1,14 @@
 # What is an ELF file?
 
+https://refspecs.linuxfoundation.org/elf/elf.pdf
 https://wiki.osdev.org/ELF
 
 ELF is a format for storing programs or fragments of programs on disk, created as a result of compiling and linking. An ELF file is divided into sections. For an executable program, these are the _text_ section for the code, the _data_ section for global variables and the _rodata_ section which usually contains constant strings. The ELF file contains headers that describe how these sections should be stored in memory. Because of this, multiple ELF files can be loaded and dynamically linked together at runtime into a single program in memory.
 
 The kernel's ELF file loader is responsible for finding the symbols that are required by the program, resolving any conflicts, and loading them into memory. Linking is performed in memory at runtime.
 
+- Type, struct, macro definitions [commit]()
+
 ## Loading ELF files
 
 The ELF header contains all of the relevant information required to load an ELF executable. The format of this header is described in the [ELF Specification](http://www.skyfree.org/linux/references/ELF_Format.pdf). The most relevant sections for this purpose are 1.1 to 1.4 and 2.1 to 2.7. Instructions on loading an executable are contained within section 2.7.

src/loader/format/elf.c

@@ -0,0 +1,9 @@
+#include "elf.h"
+
+status_t
+load_elf_executable_file(int fd, void** out_ptr, size_t* out_size)
+{
+    status_t result = ALL_OK;
+
+    return result;
+}

src/loader/format/elf.h

@@ -0,0 +1,155 @@
+#ifndef FORMAT_ELF_H
+#define FORMAT_ELF_H
+
+#include "status.h"
+#include <stddef.h>
+#include <stdint.h>
+
+typedef uint32_t Elf32_Addr; // Unsigned program address
+typedef uint16_t Elf32_Half; // Unsigned medium integer
+typedef uint32_t Elf32_Off;  // Unsigned file offset
+typedef int32_t Elf32_Sword; // Signed large integer
+typedef uint32_t Elf32_Word; // Unsigned large integer
+
+// Program Header
+// p_flags - Segment Flag Bits
+#define PF_X        0x01
+#define PF_W        0x02
+#define PF_R        0x04
+#define PF_MASKPROC 0xF0000000
+
+// p_type - Segment Types
+#define PT_NULL    0x00
+#define PT_LOAD    0x01
+#define PT_DYNAMIC 0x02
+#define PT_INTERP  0x03
+#define PT_NOTE    0x04
+#define PT_SHLIB   0x05
+#define PT_PHDR    0x06
+#define PT_LOPROC  0x70000000
+#define PT_HIPROC  0x7FFFFFFF
+
+// sh_type - Section Types
+#define SHT_NULL     0x00
+#define SHT_PROGBITS 0x01
+#define SHT_SYMTAB   0x02
+#define SHT_STRTAB   0x03
+#define SHT_RELA     0x04
+#define SHT_HASH     0x05
+#define SHT_DYNAMIC  0x06
+#define SHT_NOTE     0x07
+#define SHT_NOBITS   0x08
+#define SHT_REL      0x09
+#define SHT_SHLIB    0x0A
+#define SHT_DYNSYM   0x0B
+#define SHT_LOPROC   0x70000000
+#define SHT_HIPROC   0x7FFFFFFF
+#define SHT_LOUSER   0x80000000
+#define SHT_HIUSER   0xFFFFFFFF
+
+// e_type - Object File Types
+#define ET_NONE   0x00
+#define ET_REL    0x01
+#define ET_EXEC   0x02
+#define ET_DYN    0x03
+#define ET_CORE   0x04
+#define ET_LOPROC 0xFF00
+#define ET_HIPROC 0xFFFF
+
+// e_ident - ELF Identification
+#define EI_MAG0    0
+#define EI_MAG1    1
+#define EI_MAG2    2
+#define EI_MAG3    3
+#define EI_CLASS   4
+#define EI_DATA    5
+#define EI_VERSION 6
+#define EI_PAD     7
+#define EI_NIDENT  16 // Size of e_ident[]
+
+// ei_class - ELF Class
+#define ELFCLASSNONE 0x00
+#define ELFCLASS32   0x01
+#define ELFCLASS64   0x02
+
+// ei_data - ELF Data Encoding
+#define ELFDATANONE 0x00
+#define ELFDATA2LSB 0x01
+#define ELFDATA2MSB 0x02
+
+// e_shstrndx - Section Header String Table Index
+#define SHN_UNDEF 0x00 // If the file has no section name string table, `e_shstrndx` holds the value SHN_UNDEF.
+
+typedef struct
+{
+    Elf32_Word p_type;
+    Elf32_Off p_offset;
+    Elf32_Addr p_vaddr;
+    Elf32_Addr p_paddr;
+    Elf32_Word p_filesz;
+    Elf32_Word p_memsz;
+    Elf32_Word p_flags;
+    Elf32_Word p_align;
+} __attribute__((packed)) Elf32_Phdr;
+
+// Section Header
+typedef struct
+{
+    Elf32_Word sh_name;
+    Elf32_Word sh_type;
+    Elf32_Word sh_flags;
+    Elf32_Addr sh_addr;
+    Elf32_Off sh_offset;
+    Elf32_Word sh_size;
+    Elf32_Word sh_link;
+    Elf32_Word sh_info;
+    Elf32_Word sh_addralign;
+    Elf32_Word sh_entsize;
+} __attribute__((packed)) Elf32_Shdr;
+
+// ELF Header
+typedef struct
+{
+    unsigned char e_ident[EI_NIDENT];
+    Elf32_Half e_type;
+    Elf32_Half e_machine;
+    Elf32_Word e_version;
+    Elf32_Addr e_entry;
+    Elf32_Off e_phoff;
+    Elf32_Off e_shoff;
+    Elf32_Word e_flags;
+    Elf32_Half e_ehsize;
+    Elf32_Half e_phentsize;
+    Elf32_Half e_phnum;
+    Elf32_Half e_shentsize;
+    Elf32_Half e_shnum;
+    Elf32_Half e_shstrndx;
+} __attribute__((packed)) Elf32_Ehdr;
+
+// Dynamic Structure
+typedef struct
+{
+    Elf32_Sword d_tag;
+    union
+    {
+        Elf32_Word d_val;
+        Elf32_Addr d_ptr;
+
+    } d_un;
+} __attribute__((packed)) Elf32_Dyn;
+extern Elf32_Dyn _DYNAMIC[];
+
+// Symbol Table Entry
+typedef struct
+{
+    Elf32_Word st_name;
+    Elf32_Addr st_value;
+    Elf32_Word st_size;
+    unsigned char st_info;
+    unsigned char st_other;
+    Elf32_Half st_shndx;
+} __attribute__((packed)) Elf32_Sym;
+
+status_t load_elf_executable_file(int fd, void** out_ptr, size_t* out_size);
+
+#endif