OpenEuphoria

Re: Binary conversion (machine)

• Posted by Juergen Luethje <jluethje at gmx.de> Aug 18, 2002
• 546 views

Don <Graebel at hotmail.com> wrote:

>> The following code works for me:
>> 
>> --------------------------------------------------------
>> include machine.e
>> 
>> atom mem
>> mem = allocate(4)
>> 
>> constant SwapBytes = allocate(15)
>> poke(SwapBytes, {
>>     #50,                    --    0: push eax
>>     #A1,#00,#00,#00,#00,    --    1: mov eax, [mem] (2)
>>     #0F, #C8,               --    6: bswap eax
>>     #A3,#00,#00,#00,#00,    --    8: mov [mem], eax (9)
>>     #58,                    --    D: pop eax
>>     #C3})                   --    F: ret
>> poke4(SwapBytes + 2, mem)
>> poke4(SwapBytes + 9, mem)
>> 
>> poke4(mem, #90)
>> -- poke4(mem, #12345678)  -- better for demonstration
>> 
>> printf(1, "%08x\n", peek4u(mem))
>> call( SwapBytes )
>> printf(1, "%08x\n", peek4u(mem))
>> call( SwapBytes )
>> printf(1, "%08x\n", peek4u(mem))
>> call( SwapBytes )
>> printf(1, "%08x\n", peek4u(mem))
>> 
>> free(SwapBytes)
>> free(mem)
>> --------------------------------------------------------
>> 
>> 
>> When I first tried to compile the asm code with Pete
>> Eberlein's ASM, I got the following error message:
>> 
>>   ---------------------------------
>>   ASM to Euphoria compiler (32-bit)
>>   by Pete Eberlein    Dec 29, 2001
>>   ---------------------------------
>>   Line 4: Not a valid instruction 'bswap'
>> 
>> Mmmm, must be "Line 3" ...
>> 
>> Anyway, I had to compile the asm code without the "bswap"
>> instruction, and insert the opcode manually.
>> Don, how did you get the opcode for "bswap eax"? Is there
>> a newer version of ASM.EX?
>> 
>> Regards,
>>    Juergen

> Ahh, hmm.  Same routine but poke4'd the memory location in
> directly.

Well, it was the decision of ASM.EX to do so. 

The main difference is, that ASM.EX provided a different opcode for
   mov eax, [mem]

----------------------------------------------------------------------
-- Here's again your program, with (concerning the asm code) only this
-- one byte changed, and it works!

include machine.e

atom mem, SwapBytes
sequence Code_Space

mem = allocate( 4 )
poke4( mem, #12345678 )

Code_Space =
{
    #50,                        -- push eax
--  #B8} & int_to_bytes(mem) &  -- mov eax, offset mem   * old
    #A1} & int_to_bytes(mem) &  -- mov eax, offset mem   * new
{   #0F, #C8,                   -- bswap eax
    #A3} & int_to_bytes(mem) &  -- mov offset mem, eax
{   #58,                        -- pop eax
    #C3                         -- ret
}

SwapBytes = allocate( length(Code_Space) )
poke( SwapBytes, Code_Space )

printf(1, "%08x\n", peek4u( mem ))
call( SwapBytes )
printf(1, "%08x\n", peek4u( mem ))
call( SwapBytes )
printf(1, "%08x\n", peek4u( mem ))
call( SwapBytes )
printf(1, "%08x\n", peek4u( mem ))

free( SwapBytes )
free( mem )
----------------------------------------------------------------------

> I am going to have to experiment with this a little
> more when I have some time.

> And to answer your question, I have no idea about ASM.EX =)I didnt even 
> know it existed.

It did almost all the coding automatically. I think it will be worth
looking at it. AFAIK the version at
     http://www.harborside.com/~xseal/euphoria/download.html

is newer than the version in the RDS archive.

> I have two assembly compilers here I have been making
> programs in.  Well all I did was create a basic window and bswap'd eax 
> and sent it through a decompiler to see what codes it was using.

Ah, thats a good idea to get unknown opcodes.

> Put the rest of it together myself.  Got the idea from
> euphoria/dos/demo/callmach.ex.

> Don

Regards,
   Juergen