hello guys :)
I'm trying finish a code, it's a procedure with variable number of arguments, also I wanna link it with a C project, but for example,
I did this tiny code, and I cannot assemble it... could anyone help me :bgrin:
asm:
.386
.model flat,stdcall
include \masm32\include\masm32rt.inc
MyVarFunction PROTO C :DWORD,:VARARG
defparam1 equ [ebp+08h]
defparam2 equ [ebp+0ch]
defparam3 equ [ebp+10h]
defparam4 equ [ebp+14h]
defparam5 equ [ebp+18h]
.code
MyVarFunction proc C param1:DWORD,ParamVar:VARARG
push ebp
mov ebp,esp
mov eax,defparam2
mov ebx,defparam3
mov ecx,defparam4
mov edx,defparam5
invoke MessageBox,eax,ebx,ecx,edx
mov eax,defparam1
mov edx,04h
mul edx ; eax = 4*nparams
mov esp,ebp
pop ebp
ret eax ; <--- ERROR
MyVarFunction endp
end
how to would be correct? also I want to return a value in EAX
c:
#include <windows.h>
extern unsigned long MyVarFunction(DWORD param1,...);
int main()
{
MyVarFunction(4,0,"my test","tittle",MB_OK);
return 0;
}
in c file i think it's correct :P
Your code assembles fine if
- you use ret, not ret eax (there is no magic other register or whatever value that could be returned, so ret = return something in eax)
- you insert start: and end start
Now to pass a variable number of args, you need to tell the proggie how many you have passed. That is the purpose of the first arg (the last one that got pushed).
In assembler, the invoke macro takes care of adjusting the stack afterwards, if you use the C calling convention.
Below a complete example. If you don't have MasmBasic, replace the deb stuff with your own macro (but make sure ecx is not being trashed).
include \masm32\MasmBasic\MasmBasic.inc
.code
MyVarFunction proc C uses esi param1:DWORD,ParamVar:VARARG
lea esi, param1
lodsd
deb 4, "# args", eax
xchg eax, ecx
.Repeat
lodsd
deb 4, "Arg", eax
dec ecx
.Until Zero?
ret
MyVarFunction endp
start: invoke MyVarFunction, 3, 11, 22, 33
invoke MyVarFunction, 5, 11, 22, 33, 44, 55
inkey "bye"
exit
end start
Output:
# args eax 3
Arg eax 11
Arg eax 22
Arg eax 33
# args eax 5
Arg eax 11
Arg eax 22
Arg eax 33
Arg eax 44
Arg eax 55
bye
hi jochen, thanks you buddy :)
now I have a problem with the linking :P I already many changes to the code and I can not see the problem :P
main.obj : error LNK2001: unresolved external symbol "unsigned long __cdecl MyVarFunction(unsigned long,...)" (?MyVarFun
ction@@YAKKZZ)
main.exe : fatal error LNK1120: 1 unresolved externals
I'm just assemble it to get the obj file, then I move the obj file to path C project, I pass the obj in the VC linker :P
You must disable CPP's name mangling (or compile your project as C).
http://blogs.msdn.com/b/oldnewthing/archive/2012/05/25/10310148.aspx
RHL,
When you use the C calling convention, you normally pass an argument count then the arguments. The procedure you call must be designed to handle the variable number of arguments. The reason why you only use RET is because the code that does the calling must balance the stack after the call.
In MASM notation you would have this basic logic.
invoke MyCfunc,argcount,arg1,arg2,arg3 etc ....
The MASM procedure then is like this.
MyCfunc proc C argcount:DWORD,args:VARARG
; you code that evaluates the arg count etc ....
ret
MyCfunc endp
thanks for the replys
qWord: My C project has a .C file... not Cpp :P I tried that, but did not work , qWord
hutch: I changed the code, hutch, but still I can not compile it
my current code:
.C
#include <windows.h>
extern unsigned long MyVarFunction(DWORD,...);
int main()
{
MyVarFunction(4,0,"my test","tittle",MB_OK);
return 0;
}
.asm
.386
.model flat,stdcall
include \masm32\include\masm32rt.inc
MyVarFunction PROTO C :DWORD,:VARARG
defparam1 equ [ebp+08h]
defparam2 equ [ebp+0ch]
defparam3 equ [ebp+10h]
defparam4 equ [ebp+14h]
defparam5 equ [ebp+18h]
.code
MyVarFunction proc C param1:DWORD,ParamVar:VARARG
push ebp
mov ebp,esp
mov eax,defparam2
mov ebx,defparam3
mov ecx,defparam4
mov edx,defparam5
invoke MessageBox,eax,ebx,ecx,edx
mov esp,ebp
pop ebp
ret
MyVarFunction endp
end
main.obj : error LNK2001: unresolved external symbol "unsigned long __cdecl MyVarFunction(unsigned long,...)" (?MyVarFunction@@YAKKZZ)
I have two-three hours trying to compile my code, and still I can not :( lol
Try this one :
extern "C" unsigned long MyVarFunction(DWORD,...);
Testproc.asm (with the test code components commented out):
;==============================================================================
;include \masm32\include\masm32rt.inc
.386
.model flat,stdcall
;==============================================================================
.data
.code
;==============================================================================
;-----------------------------------------------------------------------------
; This derived from an old 16-bit example in the MASM 6.0 Programmer's Guide.
;
; The code prefixed with ";;" is generated by MASM, included here to show
; what the default prologue and epilogue are adding to the procedure.
;-----------------------------------------------------------------------------
addup proc C argCount:DWORD, args:VARARG
;;push ebp
;;mov ebp, esp
xor eax, eax ; zero work reg
xor edx, edx ; zero arg index
mov ecx, argCount
test ecx, ecx
jnz @F
;;leave
ret ; return if zero args
@@:
add eax, args[edx*4] ; add eax,[ebp+edx*4+12]
add edx, 1 ; adjust to next arg
sub ecx, 1
jnz @B
;;leave
ret
addup endp
;==============================================================================
start:
;==============================================================================
comment |
invoke addup, 0
printf("%d\n", eax )
invoke addup, 1, 1
printf("%d\n", eax )
invoke addup, 2, 1, 2
printf("%d\n", eax )
invoke addup, 3, 1, 2, 3
printf("%d\n", eax )
invoke addup, 4, 1, 2, 3, 4
printf("%d\n", eax )
inkey
exit
|
;==============================================================================
;end start
end
test.c:
#include <windows.h>
#include <conio.h>
#include <stdio.h>
extern int addup(int argCount, ... );
int main( void )
{
printf("%d\n",addup(0));
printf("%d\n",addup(1,1));
printf("%d\n",addup(2,1,2));
printf("%d\n",addup(3,1,2,3));
printf("%d\n",addup(4,1,2,3,4));
getch();
}
And the batch file that I used to compile:
set file="test"
set PATH=C:\Program Files\Microsoft Visual C++ Toolkit 2003\bin;%PATH%
set INCLUDE=C:\Program Files\Microsoft SDK\include;C:\Program Files\Microsoft Visual C++ Toolkit 2003\include;%INCLUDE%
set LIB=C:\Program Files\Microsoft SDK\Lib;C:\Program Files\Microsoft Visual C++ Toolkit 2003\lib;%LIB%
cl /W4 /FA %file%.c testproc.obj
pause
It is obviously that you compile it as C++. If you are using visual studio, you must use the /TC command line switch to force C.
:shock:
thanks a lot Vortex, I think it was referring qWord :redface: thanks people! :biggrin:
EDIT: Thanks MichaelW for your example!
EDIT: oh! now I understand what he meant, hutch :O I'm sorry guys but sometimes I do not understand :lol:
One more thing, you do not need to limit yourself to .386 code unless you are writing code for a very old 386 processor. If your code is for any modern Windows version, use this.
.686p
.mmx
.xmm
This will allow you to use any instruction in any version of MASM.
In case that doesn't work, here a very simple example of C code named jjCalc.cpp that can be linked to assembler.
commandline:
"%ProgramFiles%\Microsoft Visual Studio 10.0\VC\bin\cl.exe" /c /Oty2 /Zl /EHsc /Gs /GS- /FojjCalc.obj /Fa jjCalc.cpp
extern "C"
int _fltused=1; //get rid of a stupid error message
extern "C"
int _stdcall jjMult(int x , int y)
{
return(x*y);
}
(from \masm32\MasmBasic\MB2C\CalcTest.asc)
Quote from: hutch-- on June 24, 2012, 06:37:04 PM
When you use the C calling convention, you normally pass an argument count then the arguments.
There are exceptions to this, of course. One notable one would be an implementation of
sprintf(), where the number of arguments after the first two (the receiving buffer and the format string) depends on the number of fields found in the format string (each field, such as "%s", should have an argument pushed on the stack).
Other than that, what you said.
Quote from: qwordIf you are using visual studio, you must use the /TC command line switch to force C.
Or change the file extension to .c. If the file extension is .c (versus .cpp), it forces visual studio to C mode also.