Where is the "Section to segment mapping" stored in ELF files?

I did a test according to the @Employed Russian.

readelf -l ./libandroid_servers.so

Elf file type is DYN (Shared object file)
Entry point 0x0
There are 6 program headers, starting at offset 52

Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
  PHDR           0x000034 0x00000034 0x00000034 0x000c0 0x000c0 R   0x4
  LOAD           0x000000 0x00000000 0x00000000 0x0f830 0x0f830 R E 0x1000
  LOAD           0x010000 0x00010000 0x00010000 0x00cf4 0x011ac RW  0x1000
  DYNAMIC        0x010540 0x00010540 0x00010540 0x00130 0x00130 RW  0x4
  GNU_STACK      0x000000 0x00000000 0x00000000 0x00000 0x00000 RW  0
  EXIDX          0x00f2e8 0x0000f2e8 0x0000f2e8 0x00548 0x00548 R   0x4

 Section to Segment mapping:
  Segment Sections...
   00     
   01     .hash .dynsym .dynstr .rel.plt .rel.dyn .plt .text .rodata .ARM.extab .ARM.exidx 
   02     .init_array .fini_array .data.rel.ro .dynamic .got .data .bss 
   03     .dynamic 
   04     
   05     .ARM.exidx 

01 LOAD offset： 0x000000 fileSize 0x0f830
.ARM.exidx section end addr： hex(0x00f2e8 + 0x00548) = 0xf830

02 LOAD offset: 0x010000 fileSize: 0x00cf4
.init_array section begin addr： 10000h
.bss section end addr： hex(0x00f2e8 + 0 ) = 0x10cf4

You see the readelf surely print the sections in a segments by computes. They match well.

I still don't quite understand where section to segment mappings are stored.

They are not stored anywhere.

Rather, readelf computes the mapping by looking at file offset and size of sections and segments.