C++ __asm Generating different bytes

Question

In my function I use

__asm
{
  mov     ecx,dword ptr [0x28F1431]
  mov     ecx,ds:[0x28F14131]
}

which should produce the following bytes: 0x8B0D (mov ecx, dword ptr []). However the first instruction produces 0xB9 (mov ecx,0x28F14131) and the second one 0x3E:8B0D

So my question is, what instruction should I use to get the desired result inside the C++ __asm?

Answer 1

If you know for 100% certain what your byte sequence is supposed to be for your inlined assembly, you can always explicitly use those bytes. The exact syntax escapes me, but if you are using GCC, you may try ....

__asm {
    .byte 0x##
    .byte 0x##
    ...
}

This approach only works if you know with 100% certainty what the byte sequences for the whole instruction are. AND if you are going to do this, be sure to comment appropriately.

(For what it is worth, I have had to use this approach in the past to work around a compiler bug where no matter what it would otherwise use the wrong byte sequence for one of the instructions.)