In which segment is shstrtable?

I'm working with elf64 files and i was wondering two things, the first is, in which segment the shstrtable is stored, because reviewing readelf -l doesn't appear. And the other question (coming from the first one) is it possible for a section not be inside a segment?

Also i noticed some 'gaps' between some segments. What is inside those gaps?

I am using the following example, that is an hello_world.c:

readelf -lW hello                                          

El tipo del fichero elf es DYN (Fichero objeto compartido)
Entry point 0x1040
There are 11 program headers, starting at offset 64

Encabezados de Programa:
  Tipo           Desplaz  DirVirt            DirFísica          TamFich  TamMem   Opt Alin
  PHDR           0x000040 0x0000000000000040 0x0000000000000040 0x000268 0x000268 R   0x8
  INTERP         0x0002a8 0x00000000000002a8 0x00000000000002a8 0x00001c 0x00001c R   0x1
      [Requesting program interpreter: /lib64/ld-linux-x86-64.so.2]
  LOAD           0x000000 0x0000000000000000 0x0000000000000000 0x000560 0x000560 R   0x1000
  LOAD           0x001000 0x0000000000001000 0x0000000000001000 0x0001e5 0x0001e5 R E 0x1000
  LOAD           0x002000 0x0000000000002000 0x0000000000002000 0x000118 0x000118 R   0x1000
  LOAD           0x002de8 0x0000000000003de8 0x0000000000003de8 0x000248 0x000250 RW  0x1000
  DYNAMIC        0x002df8 0x0000000000003df8 0x0000000000003df8 0x0001e0 0x0001e0 RW  0x8
  NOTE           0x0002c4 0x00000000000002c4 0x00000000000002c4 0x000044 0x000044 R   0x4
  GNU_EH_FRAME   0x00200c 0x000000000000200c 0x000000000000200c 0x000034 0x000034 R   0x4
  GNU_STACK      0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW  0x10
  GNU_RELRO      0x002de8 0x0000000000003de8 0x0000000000003de8 0x000218 0x000218 R   0x1

 mapeo de Sección a Segmento:
  Segmento Secciones...
   00     
   01     .interp 
   02     .interp .note.gnu.build-id .note.ABI-tag .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_r .rela.dyn .rela.plt 
   03     .init .plt .text .fini 
   04     .rodata .eh_frame_hdr .eh_frame 
   05     .init_array .fini_array .dynamic .got .got.plt .data .bss 
   06     .dynamic 
   07     .note.gnu.build-id .note.ABI-tag 
   08     .eh_frame_hdr 
   09     
   10     .init_array .fini_array .dynamic .got

Solution

in which segment the shstrtable is stored, because reviewing readelf -l doesn't appear.

It doesn't appear in any segment.

And the other question (coming from the first one) is it possible for a section not be inside a segment?

Yes.

Also i noticed some 'gaps' between some segments. What is inside those gaps?

Nothing. Segments tell the kernel or the runtime loader how to mmap the on-disk binary into memory. Since mmap operates on whole pages (4096 bytes here), the contents of memory between 0x560 and 0xFFF will be "whatever happens to be in the file at offsets 0x560 through 0xFFF, but the program shouldn't access it and the contents is effectively undefined. See also this answer.