flat assembler - Fun with CPP - APP (Assembly language PreProcessor)

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Mike Gonta

Joined: 26 Dec 2010
Posts: 243

Mike Gonta 23 Mar 2016, 18:21

Fun with CPP - APP (Assembly language PreProcessor)
Write once, assemble anywhere (well at least with FASM and
NASM).

The actual x86 assembly language syntax is the same for
both and probably some other assemblers. It's the
directives that are different. The same program needs
different files for each assembler.

By using the C preprocessor CPP to #define FASM define('s)
and NASM %define('s) the same file can be assembled by both.
Similarly, CPP can #include FASM include('s) and NASM
%include('s). For those directives which are different and not
supported by CPP such as FASM rb and NASM resb a few
lines at the top will take care of it. Also FASM and NASM
differ on what can be equ(ated), whereas CPP merely
#define('s) everything. And don't forget the use of CPP
multiline comments /* */.

Code:

//#define NASM /* uncomment if using NASM */
//#define FASM /* uncomment if using FASM */
#ifdef NASM
  #define rb(value) resb value
#endif
#ifdef FASM
  #define rb(value) rb value
#endif

label: rb(0x200)

Put the C preprocessor (on Windows the gcc package contains
cpp.exe and cc1.exe both of which are required) in the same
folder or specify the location in the path statement. The
same goes for your assembler of choice (try both to confirm
that this does indeed work or have a look at the *.2 file
which is sent to the assembler).

** Windows command line script **
app.cmd yourfile.asm

Code:

  @echo off
:: for some Linux reason cpp needs to be told where it is
  set current_path=%~p0
  path=%current_path%;%path%
  if exist %~n1.2 del %~n1.2
  cpp.exe %1 > %~n1.1
:: preprocess cpp to get rid of cpp comments that begin
:: with "#"
  for /f "delims=" %%a in (%~n1.1) do (
    set AA=%%a
    @setlocal enabledelayedexpansion
    if not "!AA:~0,1!"=="#" (
      echo !AA! >> %~n1.2
    )
    @endlocal
  )
:: uncomment your assembler of choice and fix up the
:: command line for your format if not "bin"
rem  fasm %~n1.2
rem  nasm %~n1.2 -o %~n1.bin
  pause

An experienced Linux user could contribute a similar
bash script for use on Linux.

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Mike Gonta
look and see - many look but few see

https://mikegonta.com

Last edited by Mike Gonta on 24 Mar 2016, 11:13; edited 1 time in total

23 Mar 2016, 18:21

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20300
Location: In your JS exploiting you and your system

revolution 23 Mar 2016, 23:40

Interesting.

But, umm, why would I want to run NASM when I already have FASM? Confused

23 Mar 2016, 23:40

Mike Gonta

Joined: 26 Dec 2010
Posts: 243

Mike Gonta 23 Mar 2016, 23:59

revolution wrote:

Interesting.
But, umm, why would I want to run NASM when I already have FASM?

Mike Gonta wrote:

(try both to confirm that this does indeed work or have a look at the *.2 file which is sent to the assembler)

And you don't need to run NASM.
I have FASM and I also have NASM, but I prefer FASM.
It's simply a matter of writing one set of assembly language files that will assemble on both FASM and NASM and
probably some other intel syntax assemblers (but not MASM or GAS).

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Mike Gonta
look and see - many look but few see

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23 Mar 2016, 23:59

Mike Gonta

Joined: 26 Dec 2010
Posts: 243

Mike Gonta 24 Mar 2016, 00:06

Here's a self preprocessing, self assembling "Hello World!" Windows command script.
Make a folder and place the script in it. Edit the "path" command in the script
or make additional folders to contain the programs needed. FASM, the CPP (in this case cpp.exe
and cc1.exe from GCC) and QEMU (BOCHS won't emulate a 512 byte hard drive). The "hello.inc"
file is also required. This file is #include"(d) by and contains the "#define" used in the "hello.cmd" file.
hello.cmd

Code:

;  @echo off
;  set current_path=%~p0
;  path=%current_path%;%current_path%cpp;%current_path%fasm;%current_path%nasm;%current_path%qemu;%path%
;:: for some linux reason cpp needs to be told where it is
;  if exist %~n0.2 del %~n0.2
;  cpp.exe %0 > %~n0.1
;:: pre-process cpp to get rid of cpp comments that begin
;:: with "#"
;  for /f "delims=" %%a in (%~n0.1) do ( 
;    set AA=%%a
;    setlocal enabledelayedexpansion
;    if not "!AA:~0,1!"=="#" (
;      echo !AA! >> %~n0.2
;    )
;    @endlocal
;  )
;  del %~n0.1
;:: uncomment your assembler of choice and fix up the
;:: command line for your format if not "bin"
;  fasm %~n0.2
;rem  nasm %~n0.2 -o %~n0.bin
;  del %~n0.2
;  pause
;  start %current_path%qemu\qemu -L %current_path%qemu\ -name "Assembly language PreProcessor" -m 1000 -localtime -hda %~n0.bin -display sdl
;  goto finish

/***************************************

 this is a simple Hello World! example

***************************************/
org 0x7C00
start:
#include "hello.inc"
  xor ax, ax
  mov ds, ax
  mov si, hello
  mov ah, 0xE
  xor bx, bx
.1:
  lodsb
  test al, al
  je $
  int 0x10
  jmp .1

hello db HELLO
  times 510-($-$$) db 0
  dw 0xAA55

;:finish

hello.inc

Code:

#define HELLO "Hello Assembly Language PreProcessor World!",0

And here is the resulting file that is passed to the assembler

Code:

org 0x7C00
start: 
  xor ax, ax 
  mov ds, ax 
  mov si, hello 
  mov ah, 0xE 
  xor bx, bx 
.1: 
  lodsb 
  test al, al 
  je $ 
  int 0x10 
  jmp .1 
hello db "Hello Assembly Language PreProcessor World!",0 
  times 510-($-$$) db 0 
  dw 0xAA55

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Last edited by Mike Gonta on 24 Mar 2016, 15:16; edited 1 time in total

24 Mar 2016, 00:06

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20300
Location: In your JS exploiting you and your system

revolution 24 Mar 2016, 00:37

Mike Gonta wrote:

And you don't need to run NASM.

I am happy to read that Smile

Mike Gonta wrote:

(but not MASM or GAS).

I am happy to read that also Smile

So all I need is fasm, right? Razz

But perhaps this is more useful for someone who mixes C/C++ with fasm?

24 Mar 2016, 00:37

Mike Gonta

Joined: 26 Dec 2010
Posts: 243

Mike Gonta 24 Mar 2016, 00:54

revolution wrote:

So all I need is fasm, right?

Right. But you're missing the point.This will assemble on FASM but not on NASM:

Code:

org 0x7C00
start:
include "hello.inc"
  xor ax, ax
  mov ds, ax
  mov si, hello
  mov ah, 0xE
  xor bx, bx
.1:
  lodsb
  test al, al
  je $
  int 0x10
  jmp .1

hello db HELLO
  times 510-($-$$) db 0
  dw 0xAA55

And this will assemble on NASM but not on FASM:

Code:

org 0x7C00
start:
%include "hello.inc"
  xor ax, ax
  mov ds, ax
  mov si, hello
  mov ah, 0xE
  xor bx, bx
.1:
  lodsb
  test al, al
  je $
  int 0x10
  jmp .1

hello db HELLO
  times 510-($-$$) db 0
  dw 0xAA55

They are both same and yet the directives are different.
This will assemble on both after preprocessing with CPP:

Code:

/***************************************

 this is a simple Hello World! example

***************************************/
org 0x7C00
start:
#include "hello.inc"
  xor ax, ax
  mov ds, ax
  mov si, hello
  mov ah, 0xE
  xor bx, bx
.1:
  lodsb
  test al, al
  je $
  int 0x10
  jmp .1

hello db HELLO
  times 510-($-$$) db 0
  dw 0xAA55

_________________
Mike Gonta
look and see - many look but few see

https://mikegonta.com

Last edited by Mike Gonta on 24 Mar 2016, 15:15; edited 1 time in total

24 Mar 2016, 00:54

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20300
Location: In your JS exploiting you and your system

revolution 24 Mar 2016, 01:32

Okay, further to this, how does this handle macro blocks? Postpone? Format? Register arithmetic?

24 Mar 2016, 01:32

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