Structure

•  Programme header
• Section
• Symbol table

Programme header

• An executable or shared object file's program header table is an array of structures.
• each describing a segment or other information the system needs to prepare the program for execution.
• An object file segment contains one or more sections.
• Program headers are meaningful only for executable and shared object files.
• A file specifies its own program header size with the ELF header's e_phentsize and e_phnum members.

• typedef struct {
  • Elf32_Word p_type;//tells what kind of segment this array element describes or how to interpret the array element's information.
  • Elf32_Off p_offset;//gives the offset from the beginning of the file at which the first byte of the segment resides.
  • Elf32_Addr p_vaddr;//gives the virtual address at which the first byte of the segment resides in memory.
  • Elf32_Addr p_paddr; //On systems for which physical addressing is relevant, this member is reserved for the segment's physical address.
  • Elf32_Word p_filesz; //This member gives the number of bytes in the file image of the segment; it may be zero.
  • Elf32_Word p_memsz; //This member gives the number of bytes in the memory image of the segment; it may be zero.
  • Elf32_Word p_flags; //This member gives flags relevant to the segment.
  • Elf32_Word p_align; //This member gives the value to which the segments are aligned in memory and in the file.
• } Elf32_Phdr;

• p_type
  • • Name 　    　　　    Value 　　          meaning
    • PT_NULL 　　　　   0                          The array element is unused
    • PT_LOAD 　　　　   1                           The array element specifies a loadable segment
    • PT_DYNAMIC 　　   2                           The array element specifies dynamic linking information
    • PT_INTERP　　　    3                           The array element specifies the location and size of a null- terminated path name to invoke as an interpreter
    • PT_NOTE 　　　　  4         　　           The array element specifies the location and size of auxiliary information
    • PT_SHLIB 　　　     5                             This segment type is reserved, has unspecified semantics
    • PT_PHDR 　　　     6                             specifies the location and size of the program header table itself
    • PT_LOPROC 　       0x70000000         reserved for processor-specific semantics
    • PT_HIPROC 　　    0x7fffffff