What is the purpose of 00 segment?

[Peng Yu]

Hi,

The following example shows there are two segments. But only the 2nd
segment is relevant to .text. The 1st segment just contains the ELF
header and something (is the "something" relevant to running the
program?). If the first segment is removed, the program still runs?

I don't get why the first segment is there. Can anybody explain? Thanks.

$ cat main.asm
global  _start
_start:
SYS_EXIT equ 60
mov     rax, SYS_EXIT
mov     rdi, 42
syscall
$ nasm -felf64 main.asm
$ ld -o main.exe main.o
$ readelf -lW main.exe

Elf file type is EXEC (Executable file)
Entry point 0x401000
There are 2 program headers, starting at offset 64

Program Headers:
  Type           Offset   VirtAddr           PhysAddr
FileSiz  MemSiz   Flg Align
  LOAD           0x000000 0x0000000000400000 0x0000000000400000
0x0000b0 0x0000b0 R   0x1000
  LOAD           0x001000 0x0000000000401000 0x0000000000401000
0x00000c 0x00000c R E 0x1000

 Section to Segment mapping:
  Segment Sections...
   00
   01     .text
$ readelf -SW main.exe
There are 5 section headers, starting at offset 0x1120:

Section Headers:
  [Nr] Name              Type            Address          Off    Size
 ES Flg Lk Inf Al
  [ 0]                   NULL            0000000000000000 000000
000000 00      0   0  0
  [ 1] .text             PROGBITS        0000000000401000 001000
00000c 00  AX  0   0 16
  [ 2] .symtab           SYMTAB          0000000000000000 001010
0000c0 18      3   4  8
  [ 3] .strtab           STRTAB          0000000000000000 0010d0
00002b 00      0   0  1
  [ 4] .shstrtab         STRTAB          0000000000000000 0010fb
000021 00      0   0  1
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
  L (link order), O (extra OS processing required), G (group), T (TLS),
  C (compressed), x (unknown), o (OS specific), E (exclude),
  l (large), p (processor specific)

-- 
Regards,
Peng