How to enforce the assembler to emit code using using specific encoding? [duplicate]

问题

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Closed last year.

Yesterday, I got caught a problem on re-asselembling the disassembly.
My experiment was like below. :

1. Disassemble binary_A into A.s  
2. Re-assemble A.s into binary_A'  

I expected binary_A and binary_A' to be completely identical.
However, it wasn't !


1. disassembly of binary_A was :

53                  #  push %ebx
83 ec 08            #  sub $0x8,%esp
81 c3 4b 1d 00 00   #  add $0x1d4b,%ebx
8b 83 fc ff ff ff   #  mov -0x4(%ebx),%eax      <= Here
85 c0               #  test %eax,%eax

2. I parsed it and made A.s file:

push %ebx
sub $0x8,%esp
add $0x1d4b,%ebx
mov -0x4(%ebx),%eax
test %eax,%eax

3. finally I re-assembled it into binary_A' (Look carefully at the arrow):

53                  #  push %ebx
83 ec 08            #  sub $0x8,%esp
81 c3 4b 1d 00 00   #  add $0x1d4b,%ebx
8b 43 fc            #  mov -0x4(%ebx),%eax     <= Here!
85 c0               #  test %eax,%eax

Here is my problem :
I want binary_A and binary_A' to be completely identical.
However, it wasn't because mov eax, DWORD PTR [ebx - 0x4]is assembled in a different way.

Question :
Can I direct assembler to use specific encoding?
(using assembler directive or sth like that?)

来源：https://stackoverflow.com/questions/51491342/how-to-enforce-the-assembler-to-emit-code-using-using-specific-encoding