Why do you need crt2.o in C++?

Programm Hello World (hello.s)

    .dataLC0:    .ascii "Hello, World!\0"    .text    .globl  _main_main:    pushl   %ebp    movl    %esp, %ebp    andl    $-16, %esp    subl    $16, %esp    movl    $LC0, (%esp)    call    _puts    xorl    %eax, %eax    leave    ret

1 compilation method

as.exe hello.sld -s a.out -LC:\gcc\lib -lmsvcrt -o hello.exe(2kb)

2 compilation method(standart)

as.exe hello.sgcc -s a.out -o hello.exe(12kb)

I found that the increase in the size of hello.exe is associated with the attachment of the crt2.o file. What specific function does it perform?