help needed:Which file is the key file in the ELF(for linux) linker?

[<zengshuai@sogou.com>]

//hello.c
int main()
{
    int a;
    a=1;
}
--------------------------
first time:
#gcc -c -o hello.o hello.c
#ld -o hello.elf hello.o
#file hello.elf
hello.elf: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV),
statically inked, not stripped                                                            

second time:
#gcc -c -o hello.o hello.c
#ld -static hello.o /usr/lib/crt1.o /usr/lib/crti.o /usr/
ib/crtn.o /usr/lib/gcc-lib/i386-redhat-linux/3.2.2/crtbegin.o /usr/lib/gcc-lib/
386-redhat-linux/3.2.2/crtend.o -L/usr/lib -lc /usr/lib/gcc-lib/i386-redhat-lin
x/3.2.2/libgcc.a -o hello.elf                                                   
#file hello.elf
hello.elf: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), 
for GNU/Linx 2.2.5, statically linked, not stripped                                       
~~~~~~~~~~~~~~~~~~

So,which file is the key file,which cause the change,from elf to linux elf?
How to compile a ELF file using in bareboard and how to compile a ELF file 
using in Linux really puzzles me a lot.thanks

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