How to convert from binary to portable object and vice versa?

Question

I want to add an object file to an existing binary. The method I'm trying to do:

• Convert a compiled binary to a portable object file.
• Use gcc/ldto link the file of the moved object with the attached object file.

Based on the source:

#include <stdlib.h>
#include <stdio.h>

int main(void)
{
    puts("main");
    return EXIT_SUCCESS;
}

I compile this hostwith the following:

gcc -Wall host.c -o host

I am doing a conversion to a file of a roaming object with:

objcopy -B i386 -I binary -O elf64-x86-64 host host.o

Then I will try to establish a connection with:

gcc host.o -o host

Ideally, this will cause the file to be moved back to the binary. It will also make it possible to link any additional object files. Unfortunately, the command gives the following error:

/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../x86_64-linux-gnu/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
collect2: ld returned 1 exit status

My question is why this error occurs and how will I correspond correctly?

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readelf :

mike@mike-ubuntu:~/Desktop/inject-obj$ readelf -h host
ELF Header:
  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF64
  Data:                              2 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:               0x400410
  Start of program headers:          64 (bytes into file)
  Start of section headers:          4424 (bytes into file)
  Flags:                             0x0
  Size of this header:               64 (bytes)
  Size of program headers:           56 (bytes)
  Number of program headers:         9
  Size of section headers:           64 (bytes)
  Number of section headers:         30
  Section header string table index: 27

:

mike@mike-ubuntu:~/Desktop/inject-obj$ readelf -h host.o
ELF Header:
  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF64
  Data:                              2 complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              REL (Relocatable file)
  Machine:                           Advanced Micro Devices X86-64
  Version:                           0x1
  Entry point address:               0x0
  Start of program headers:          0 (bytes into file)
  Start of section headers:          8480 (bytes into file)
  Flags:                             0x0
  Size of this header:               64 (bytes)
  Size of program headers:           0 (bytes)
  Number of program headers:         0
  Size of section headers:           64 (bytes)
  Number of section headers:         5
  Section header string table index: 2

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Answer 1

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