Modyfing array variable in compilation time

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alorent

Joined: 05 Dec 2005
Posts: 201

alorent

Hi guys,

I have a non common issue that not sure how it can be addressed.

I have a variable which defines a list of pointers to functions:

Code:

pListFunctions dd 10 dup (0)

I would like that a separate coder create his functions and they are added to "pListFunctions" in *compilation time*. So, in runtime, I just have to walk over "pListFunctions" and just call each function on the list.

I was thinking that a separate coder could define his function and he just use a macro (let's call it ADD_FUNCTION) which automatically adds the function pointer to "pListFunction" (but in compilation time!). Example:

Code:

Function1 proc 

    ....
    ret 

Function1 endp

ADD_FUNCTION Function1

Would the above could be implemented in FASM?

Thanks!

25 Apr 2010, 19:50

edfed

Joined: 20 Feb 2006
Posts: 4242
Location: 2018

edfed

i think it is.
macro support local variable, but supoprt global variables too.

then, define a global pointer(equate?) to your array
use the global pointer as an offset in the array
update the pointer.

in practice i don't know how to do.

maybe it would be easier to create a function ot do this, and not a macro.

and use a macro to call this fucntion

macro add_func func{
push func
call addfunc
}
call

25 Apr 2010, 20:29

Tyler

Joined: 19 Nov 2009
Posts: 1216
Location: NC, USA

Tyler

If only I could find a way to store the address, I attempted to store the pointer with the last line but I get a weird error, "Error: code cannot be generated."

Code:

if ~functions_added = 0
   pListFunctions rd functions_added
end if
macro add_func addr
{
   if ~functions_added = 0
      functions_added = functions_added + 1
   else
      functions_added = 1
   end if
   store dword addr at (pListFunctions + (functions_added - 1) * 4)
}

25 Apr 2010, 21:08

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4633
Location: Argentina

LocoDelAssembly

Tyler, take a look at this:

Code:


   pListFunctions rd functions_added_final
   functions_added = 0

macro add_func addr
{
   functions_added = functions_added + 1
   store dword addr at (pListFunctions + (functions_added - 1) * 4)
}

alpha:ret
beta:ret
gamma:rep ret
epsilon:ret

add_func alpha
add_func gamma
add_func epsilon

functions_added_final = functions_added

25 Apr 2010, 21:34

Tyler

Joined: 19 Nov 2009
Posts: 1216
Location: NC, USA

Tyler

Loco: Nice, I was trying to keep everything self contained so that the variables were only processed if the macro was used, which complicated mine a little complicated. I still don't see where I screwed up.

I think this works, not so sure how to test it though. It assemblers w/o an error.

Code:

if defined functions_added
   pListFunctions rd functions_added
end if
macro add_func addr
{
   if ~(defined functions_added)
      functions_added = functions_added + 1
   else
      functions_added = 1
   end if
   store dword addr at (pListFunctions + (functions_added - 1) * 4)
}

25 Apr 2010, 21:50

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4633
Location: Argentina

LocoDelAssembly

invoke add_func twice or more and you'll get an out of scope error. I'm not sure what was causing the "code cannot be generated" error in your earlier version, I was expecting something like the error you get now with multiple invocations of add_func.

25 Apr 2010, 21:56

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr

alorent,

Would comma-separated list of labels suffice? You may use something like

Code:

macro append name, [value] {
common
  match old_value, name \{
    restore name
    name equ old_value, value
  \}
  match , name \{ ; list is empty, no separator necessary
    restore name
    name equ value
  \}
}

Usage is simple:

Code:

labels_list equ
...
append labels_list, Function1, Function2; and so on; 10 dup FunctionX is also valid 
...
pListFunctions dd labels_list

25 Apr 2010, 22:42

alorent

Joined: 05 Dec 2005
Posts: 201

alorent

Hello guys,

Thanks a lot for your help.

Tyler, Loco: 1st of all, THANKS! I have tried your solutions, but when I write:

add_func MyProc

I get a compiler error "value out of range"

Not sure if I have to call it in a different way.

baldr: Thanks for giving another solution. Unfortunatelly, I cannot use that approach. The functions must be added independently (from different modules) and not setting up the whole list at once.

Thanks!

26 Apr 2010, 10:42

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr

alorent,

That macro doesn't build list at once, it appends its arguments to list and can be invoked multiple times. Like any other preprocessor solution, the resulting list can be used only after the last append macro invocation.

LocoDelAssembly's solution works OK for me. Note that exact order is important: functions_added = 0 should be before first add_func invocation, functions_added_final = functions_added should be after last (included files can mess with that).

26 Apr 2010, 14:49

alorent

Joined: 05 Dec 2005
Posts: 201

alorent

Hello baldr,

Thanks for the information. Sorry, I thought that your solution created the list at once.

I have tried to use your solution but I think that I'm not doing it in the correct way:

Code:

include 'win32ax.inc' ; you can simply switch between win32ax, win32wx, win64ax and win64wx here
include 'macro\if.inc' 
include 'macro\masm.inc'

macro append name, [value] {
common 
  match old_value, name \{ 
    restore name 
    name equ old_value, value 
  \} 
  match , name \{ ; list is empty, no separator necessary 
    restore name 
    name equ value 
  \} 
}

.data 

labels_list:
dd 10 dup (0)


pListFunctions dd labels_list


.code 

start: 


append labels_list, MyProc
append labels_list, MyProc2

int 3
mov  eax, pListFunctions


MyProc proc

 ret

MyProc endp

MyProc2 proc

 ret

MyProc2 endp

.end start

The resulting list is empty. Any ideas?

Thanks!

26 Apr 2010, 17:27

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr

alorent,

You got it all the way wrong. Wink

Code:

include 'win32ax.inc' ; you can simply switch between win32ax, win32wx, win64ax and win64wx here
include 'macro\if.inc' 
include 'macro\masm.inc'

macro append name, [value] {
common 
  match old_value, name \{ 
    restore name 
    name equ old_value, value 
  \} 
  match , name \{ ; list is empty, no separator necessary 
    restore name 
    name equ value 
  \} 
}
labels_list equ

append labels_list, MyProc
append labels_list, MyProc2

.data

pListFunctions dd labels_list

.code

start: 


int 3
mov  eax, pListFunctions


MyProc proc

 ret

MyProc endp

MyProc2 proc

 ret

MyProc2 endp

.end start

append invocations can be anywhere between labels_list equ and pListFunctions dd labels_list but the order is important.

27 Apr 2010, 05:37

alorent

Joined: 05 Dec 2005
Posts: 201

alorent

Thanks baldr!

Will that approach work on multiple asm files (linked as OBJ files) on a single list? That is, each module call its own "append" macros? Finally, one module (asm) will be the one that reads the whole list and process it.

Thanks!!

27 Apr 2010, 13:11

Tyler

Joined: 19 Nov 2009
Posts: 1216
Location: NC, USA

Tyler

No, you asked for something that affected code at compile time. Macros are processed before even the object code would be made.

You could do it at runtime, but I don't know of how to do such a thing with a linker because I don't use one. If you were to "link" the files by preprocessor-including them, it would work fine.

28 Apr 2010, 03:02

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr

alorent,

"Modyfing array variable in compilation time", heh?

Well, even at link stage it is possible: linker merges similar (up to "$something" name suffix) sections.

Code:

; This is the main source
format MS COFF
section ".text" executable
        public  start
start:
        mov     eax, pListFunctions
        mov     ecx, pListFunctionsEnd
        ret

section ".data$a" readable
pListFunctions:

section ".data$c" readable
pListFunctionsEnd:

Code:

; This is the first function
format MS COFF
section ".text" executable
Function1:
        mov     eax, 1
        ret

section ".data$b" readable
        dd      Function1

Code:

; This is the second function
format MS COFF
section ".text" executable
Function2:
        mov     eax, 2
        ret

section ".data$b" readable
        dd      Function2

Those section / dd sequences are the equivalent of add_func macro (and can be made such). Alas, pListFunctionsEnd-pListFunctions can't be computed at compile time, much less (pListFunctionsEnd-pListFunctions)/4 (can any linker perform simple computations with relocations?). Macro can count them.

28 Apr 2010, 07:39

alorent

Joined: 05 Dec 2005
Posts: 201

alorent

Thanks baldr!!! Very Happy

That's another approach! Wink

29 Apr 2010, 07:11

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