Can different source code generate the same executable/binary file?

Question

Can different source code generate the same executable/binary file?

Is this possible?

Answer 1

Yes. Compilers can make a lot of optimizations, and different source code can map to the same object code. Here are a couple trivial examples. Note that these are language-dependent.

• You can express an integer in decimal, hex, octal, or binary--the result in the object code will be the same.
• In many languages, the variable names do not appear in the executable, and you can change the names of variables without affecting the executable.

Answer 2

Yes. For example

int nabs1(int a){ 
  return -abs(a); 
}

int nabs2(int a){ 
  return(a<0) ? a : -a;
}

gcc -O6 generates the same code:

 _nabs1:
pushl   %ebp
movl    %esp, %ebp
movl    8(%ebp), %edx
popl    %ebp
movl    %edx, %eax
sarl    $31, %eax
xorl    %eax, %edx
subl    %edx, %eax
ret
.p2align 4,,15
.globl _nabs2
.def    _nabs2; .scl    2;  .type   32; .endef
_nabs2:
pushl   %ebp
movl    %esp, %ebp
movl    8(%ebp), %edx
popl    %ebp
movl    %edx, %eax
sarl    $31, %eax
xorl    %eax, %edx
subl    %edx, %eax
ret