ELF sections not being mapped to segments as expected

Question

I am writing a compiler and am just starting to generate ELF executables from scratch. I am creating a .text section (although it doesn't have a name because I am not creating a string table yet), and trying to put it within a PT_LOAD segment. However, readelf isn't reporting that the section is mapped into the segment and objdump refuses to disassemble the code in the .text section. This is the readout of readelf, with some bits omitted for brevity:

ELF Header:
  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF64
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           Advanced Micro Devices X86-64
  Version:                           0x1
  Entry point address:               0x0
  Start of program headers:          64 (bytes into file)
  Start of section headers:          122 (bytes into file)
  Flags:                             0x0
  Size of this header:               64 (bytes)
  Size of program headers:           56 (bytes)
  Number of program headers:         1
  Size of section headers:           64 (bytes)
  Number of section headers:         2
  Section header string table index: 0

Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0] <no-name>         NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] <no-name>         PROGBITS         0000000008048000  00000078
       0000000000000002  0000000000000000  AX       0     0     16
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings), l (large)
  I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown)
  O (extra OS processing required) o (OS specific), p (processor specific)

There are no section groups in this file.

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000000078 0x0000000008048000 0x0000000008048000
                 0x0000000000000002 0x0000000000000002  R E    1000

At offset 0x78, I am just emitting two push ebxs (opcode 0x53) for testing. Here is the hex dump:

00000000  7f 45 4c 46 02 01 01 00  00 00 00 00 00 00 00 00  |.ELF............|
00000010  02 00 3e 00 01 00 00 00  00 00 00 00 00 00 00 00  |..>.............|
00000020  40 00 00 00 00 00 00 00  7a 00 00 00 00 00 00 00  |@.......z.......|
00000030  00 00 00 00 40 00 38 00  01 00 40 00 02 00 00 00  |[email protected]...@.....|
00000040  01 00 00 00 05 00 00 00  78 00 00 00 00 00 00 00  |........x.......|
00000050  00 80 04 08 00 00 00 00  00 80 04 08 00 00 00 00  |................|
00000060  02 00 00 00 00 00 00 00  02 00 00 00 00 00 00 00  |................|
00000070  00 10 00 00 00 00 00 00  53 53 00 00 00 00 00 00  |........SS......|
00000080  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
000000b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 01 00  |................|
000000c0  00 00 06 00 00 00 00 00  00 00 00 80 04 08 00 00  |................|
000000d0  00 00 78 00 00 00 00 00  00 00 02 00 00 00 00 00  |..x.............|
000000e0  00 00 00 00 00 00 00 00  00 00 10 00 00 00 00 00  |................|
*
000000fa

Edit: Question - Why isn't a section to segment mapping shown between the two, and why is no disassembly shown by objdump?

Answer 1

Why isn't a section to segment mapping shown between the two

Because there are no valid sections (as far as readelf can tell).

and why is no disassembly shown by objdump?

objdump also uses sections.

Even though sections are not required for the executable part of ELF lifetime, a lot of tools depend on sections being present. For example, the lone segment you have in your executable contains both code and the ELF header, and the program header. Generally you don't want to disassemble the header. Without sections, objdump doesn't know where to start disassembly from.