Batch file doubling as a fasmg source

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Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8358
Location: Kraków, Poland

Tomasz Grysztar 09 May 2019, 11:12

Recently I came up with this fun little trick to make a batch file that could also be assembled with fasmg, and when executed would run fasmg to assemble itself:

Code:

@echo off
goto batch
end if
macro @echo off
        if 0
end macro

virtual at 0
        digits::
        n = %t / 50
        while n
             d = '0' + n mod 36
             if d > '9'
                d = d - '0' - 10 + 'a'
             end if
             n = n / 36
             db d
        end while
        count = $
end virtual
repeat count
        load d byte from digits:count-%
        display d
end repeat

macro ?! any&
end macro

:batch
fasmg %~f0 nul -n

The inner assembly script that is executed here is the one I use to generate fasmg's version number (it works either with fasm 1 or fasmg, but the trick that allowed to embed it in batch file only works with fasmg).

09 May 2019, 11:12

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20445
Location: In your JS exploiting you and your system

revolution 09 May 2019, 12:59

Is this to save having a second file on disk?

We can also do this in fasm 1 slightly differently by creating temporary files:

Code:

@echo off

echo ;This file is auto generated by %~f0    >%~f0.temp

echo virtual at 0                            >>%~f0.temp
echo         digits::                        >>%~f0.temp
echo         n = %t / 50                     >>%~f0.temp
echo         while n                         >>%~f0.temp
echo              d = '0' + n mod 36         >>%~f0.temp
echo              if d > '9'                 >>%~f0.temp
echo                 d = d - '0' - 10 + 'a'  >>%~f0.temp
echo              end if                     >>%~f0.temp
echo              n = n / 36                 >>%~f0.temp
echo              db d                       >>%~f0.temp
echo         end while                       >>%~f0.temp
echo         count = $                       >>%~f0.temp
echo end virtual                             >>%~f0.temp
echo repeat count                            >>%~f0.temp
echo         load d byte from digits:count-% >>%~f0.temp
echo         db d                            >>%~f0.temp
echo end repeat                              >>%~f0.temp

fasm %~f0.temp %~f0.temp2

copy %~f0.temp2 con

del %~f0.temp
del %~f0.temp2

Or something similar. I can't test it ATM. But the idea is there to create a temp file and the assemble it to another temp file. And after displaying the output delete the two temp files.

09 May 2019, 12:59

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8358
Location: Kraków, Poland

Tomasz Grysztar 09 May 2019, 13:33

revolution wrote:

Is this to save having a second file on disk?

Yes, but it is also just a fun thing to do, to design polyglot batch files. And polyglot files in general, that seems to be an entire form of art on its own.

09 May 2019, 13:33

edfed

Joined: 20 Feb 2006
Posts: 4353
Location: Now

edfed 13 May 2019, 07:40

very cool feature, i never use os capabilities. maybe it's time to...

This trick makes possible to postcompile generated sources , i like it. Smile

13 May 2019, 07:40

d469964

Joined: 19 Mar 2012
Posts: 3

d469964 20 May 2019, 01:18

I think you overcomplicate things:

Code:

@rem: if 0
@fasmg "%~f0" nul
@exit
end if

virtual at 0
        digits::
        n = %t / 50
        while n
             d = '0' + n mod 36
             if d > '9'
                d = d - '0' - 10 + 'a'
             end if
             n = n / 36
             db d
        end while
        count = $
end virtual
repeat count
        load d byte from digits:count-%
        display d
end repeat

Works perfectly with fasm & fasmg.

20 May 2019, 01:18

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20445
Location: In your JS exploiting you and your system

revolution 20 May 2019, 07:48

d469964 wrote:

I think you overcomplicate things:

Code:

@rem: if 0
@fasmg "%~f0" nul
@exit
end if

virtual at 0
        digits::
        n = %t / 50
        while n
             d = '0' + n mod 36
             if d > '9'
                d = d - '0' - 10 + 'a'
             end if
             n = n / 36
             db d
        end while
        count = $
end virtual
repeat count
        load d byte from digits:count-%
        display d
end repeat

Works perfectly with fasm & fasmg.

Nice.

Is there a way to also make it work with bash?

20 May 2019, 07:48

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8358
Location: Kraków, Poland

Tomasz Grysztar 20 May 2019, 08:03

d469964 wrote:

I think you overcomplicate things

I think you missed the "fun" word in my initial post. Wink

Your variant is of course great at being concise, but I designed mine to be able to accomodate existing source code and existing batch script and have them cleanly separated without a risk of having a command within the batch portion that could be misinterpreted by the assembler. In your case inserting a script containing a command like "if errorlevel" would break the assembly.

20 May 2019, 08:03

d469964

Joined: 19 Mar 2012
Posts: 3

d469964 20 May 2019, 17:18

d469964 wrote:

In your case inserting a script containing a command like "if errorlevel" would break the assembly.

It's not a problem:

Code:

@rem: if 0
@fasm "%~f0" nul 
@if errorlevel 1 (
  echo Compilation error!
  pause
)  
@goto :EOF
end if

20 May 2019, 17:18

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8358
Location: Kraków, Poland

Tomasz Grysztar 20 May 2019, 17:26

This was my point exactly - you needed to check and modify the batch commands to ensure that they are written in way that does not cause problems. The framework I proposed should allow to take a script as-is and not worry about possible interference.

20 May 2019, 17:26

d469964

Joined: 19 Mar 2012
Posts: 3

d469964 20 May 2019, 19:30

Quote:

Is there a way to also make it work with bash?

I'm not a Linux guy and create only this (bash only):

Code:

echo=0
if echo; then
  fasm "$0"
  exit
fi
end if

and this (both bash and batch, but print one line of garbage):

Code:

rem=""; : '
@rem: if 0 
@fasmg "%~f0" nul
@exit
;'
fasmg "$0"
exit
end if

20 May 2019, 19:30

Grom PE

Joined: 13 Mar 2008
Posts: 114
Location: i@grompe.org.ru

Grom PE 21 May 2019, 06:37

Thankfully the semicolon is both a comment in fasm and ignored in batch, so I was able to come up with a polyglot file with batch and fasm source completely separate:

https://github.com/grompe/kbdasm/blob/e12b8c1a41f36ecbf8d5486af1716226233e72c2/diskbd.bat

21 May 2019, 06:37

rugxulo

Joined: 09 Aug 2005
Posts: 2341
Location: Usono (aka, USA)

rugxulo 21 May 2019, 17:42

I'm no expert, but this can also be done in Perl, Ruby, etc. with .BAT. (Also, Bash shell scripts can have here docs or whatever.)

21 May 2019, 17:42

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