elf.h

#ifndef ELF_H
#define ELF_H

#include <stdint.h>

#define ELF_RELOC_ERR -1

#define ELF_IDENT_LENGTH 16
typedef struct {
    uint8_t     ident[ELF_IDENT_LENGTH];
    uint16_t    type;
    uint16_t    machine;
    uint32_t    version;
    uint32_t    entry;
    uint32_t    phoff;
    uint32_t    shoff;
    uint32_t    flags;
    uint16_t    ehsize;
    uint16_t    phentsize;
    uint16_t    phnum;
    uint16_t    shentsize;
    uint16_t    shnum;
    uint16_t    shstrndx;
} elf_header;

typedef struct {
    uint32_t    type;           /* Segment type */
    uint32_t    offset;     /* Segment file offset */
    uint32_t    vaddr;      /* Segment virtual address */
    uint32_t    paddr;      /* Segment physical address */
    uint32_t    filesz;     /* Segment size in file */
    uint32_t    memsz;      /* Segment size in memory */
    uint32_t    flags;      /* Segment flags */
    uint32_t    align;      /* Segment alignment */
} elf_phdr;

typedef struct {
    uint32_t    name;
    uint32_t    type;
    uint32_t    flags;
    uint32_t    addr;
    uint32_t    offset;
    uint32_t    size;
    uint32_t    link;
    uint32_t    info;
    uint32_t    addralign;
    uint32_t    entsize;
} elf_s_header;

typedef struct {
    uint32_t    name;
    uint32_t    value;
    uint32_t    size;
    uint8_t     info;
    uint8_t     other;
    uint16_t    shndx;
} elf_sym_tab;

#define ELF32_ST_BIND(INFO) ((INFO) >> 4)
#define ELF32_ST_TYPE(INFO)     ((INFO) & 0x0F)

enum elf_sym_tab_bindings {
    STB_LOCAL   = 0, //local scope
    STB_GLOBAL  = 1, //global scope
    STB_WEAK    = 2, //weak (__attribute__((weak)))
};

enum elf_sym_tab_types {
    STT_NOTYPE  = 0, //no type
    STT_OBJECT  = 1, //variable/array/etc
    STT_FUNC    = 2, //method/function
};

#define SHN_UNDEF   (0x00) //undefined/not present
#define SHN_ABS     (0xfff1)
enum elf_sh_types {
    SHT_NULL    = 0, //null section
    SHT_PROGBITS    = 1, //program information
    SHT_SYMTAB  = 2, //symbol table
    SHT_STRTAB  = 3, //string table
    SHT_RELA    = 4, //relocation (w/ addend)
    SHT_NOBITS  = 8, //not present in file
    SHT_REL     = 9, //relocation (no addend)
};

enum elf_sh_attr {
    SHF_WRITE   = 0x01, //writable section
    SHF_ALLOC   = 0x02, //exists in memory
};

enum elf_ident {
    EI_MAG0     = 0, //0x7F
    EI_MAG1     = 1, //'E'
    EI_MAG2     = 2, //'L'
    EI_MAG3     = 3, //'F'
    EI_CLASS    = 4, //arch (32/64)
    EI_DATA     = 5, //endianness
    EI_VERSION  = 6, //ELF version
    EI_OSABI    = 7, //OS specific
    EI_ABIVERSION   = 8, //OS specific
    EI_PAD      = 9, //padding
};

#define ELFMAG0     0x7F //ident[EL_MAG0]
#define ELFMAG1     'E'  //ident[EL_MAG1]
#define ELFMAG2     'L'  //ident[EL_MAG2]
#define ELFMAG3     'F'  //ident[EL_MAG3]
#define ELFDATA2LSB (1)  //little endian
#define ELFCLASS32  (1)  //32-bit arch

enum elf_type {
    ET_NONE     = 0, //unknown type
    ET_REL      = 1, //relocatable file
    ET_EXEC     = 2, //executable file
};

#define EM_386      (3)  //x86 type
#define EV_CURRENT  (1)  //ELF current version

typedef struct {
    uint32_t    offset;
    uint32_t    info;
} elf_rel;

typedef struct {
    uint32_t offset;
    uint32_t info;
    int32_t addend;
} elf_rela;

#define ELF_R_SYM(INFO) ((INFO) >> 8)
#define ELF_R_TYPE(INFO)((uint8_t)(INFO))

enum elf_rt_types {
    R_386_NONE  = 0, //no relocation
    R_386_32    = 1, //symbol + offset
    R_386_PC32  = 2, //symbol + offset - section offset
};

#define PT_LOAD     1
#define PT_DYNAMIC  2
#define PT_INTERP   3


void* elf_load_file(char* filename, void* file, uint32_t size);

int execve(const char *filename, char *const argv[], char *const envp[]);

#endif