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Calling a C++ function from Poasm

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Vortex:
Here is a Poasm example calling a MS VC module :


--- Code: ---#define _NO_CRT_STDIO_INLINE

#include <stdio.h>

class formula {

    public:
       
        int calc(int, int, int, int, int);
        void GetResult(int);
};

int formula::calc(int a, int b, int c, int d, int e)
{
    return a * b * c * d * e;
}

void formula::GetResult(int t)
{
    printf("The result is %u\n",t);
}

--- End code ---

rcx points the "this" pointer, it must be skipped :


--- Code: ---EXTERN ?calc@formula@@QEAAHHHHHH@Z:PROC
calc TEXTEQU <?calc@formula@@QEAAHHHHHH@Z>

EXTERN ?GetResult@formula@@QEAAXH@Z:PROC
GetResult TEXTEQU <?GetResult@formula@@QEAAXH@Z>

ExitProcess PROTO :QWORD

.code

start PROC PARMAREA=6*QWORD

;   rcx ->  this pointer

    mov     rdx,2
    mov     r8,4
    mov     r9,6
    mov     QWORD PTR [rsp+32],8
    mov     QWORD PTR [rsp+40],10
    call    calc

;   rcx ->  this pointer

    mov     rdx,rax
    call    GetResult

    invoke  ExitProcess,0

start ENDP

END start

--- End code ---

Vortex:
Same example with function prototypes :


--- Code: ---?calc@formula@@QEAAHHHHHH@Z PROTO :QWORD,:QWORD,:QWORD,:QWORD,:QWORD,:QWORD
calc TEXTEQU <?calc@formula@@QEAAHHHHHH@Z>

?GetResult@formula@@QEAAXH@Z PROTO :QWORD,:QWORD
GetResult TEXTEQU <?GetResult@formula@@QEAAXH@Z>

ExitProcess PROTO :QWORD

.code

start PROC PARMAREA=6*QWORD

;   rcx ->  this pointer

    invoke  calc,rcx,2,4,6,8,10

;   rcx ->  this pointer

    invoke  GetResult,rcx,rax

    invoke  ExitProcess,0

start ENDP

END start
--- End code ---

TimoVJL:
Why not with C  ;)
--- Code: ---void __stdcall  ExitProcess( unsigned int uExitCode);
int __cdecl printf(const char * format, ...);
#pragma comment(lib, "msvcrt.lib")
// void formula::GetResult(int t)
// void ?GetResult@formula@@QEAAXH@Z(long long, long long)
#pragma comment(linker, "-alternatename:formula_GetResult=?GetResult@formula@@QEAAXH@Z")
void formula_GetResult(void* this, int t);
// int formula::calc(int a, int b, int c, int d, int e)
// int ?calc@formula@@QEAAHHHHHH@Z(int a, int b, int c, int d, int e)
int formula_calc(void* this, int a, int b, int c, int d, int e);
#pragma comment(linker, "-alternatename:formula_calc=?calc@formula@@QEAAHHHHHH@Z")
void __cdecl mainCRTStartup(void)
{
int x = formula_calc(0,2,4,6,8,10);
formula_GetResult(0,x);
ExitProcess(0);
}
--- End code ---

Vortex:
Hi Timo,

Great sample, many thanks. Something new to learn for me, it's the /ALTERNATENAME:symbol=symbol option of polink.

The linker option ALTERNATENAME does the job, disassembling the object module produced by Pelles C :


--- Code: ---public mainCRTStartup

extern ExitProcess: near
extern formula_GetResult: near
extern formula_calc: near

_text   SEGMENT PARA 'CODE'

mainCRTStartup PROC
        sub     rsp, 56
        mov     dword ptr [rsp+28H], 10
        mov     dword ptr [rsp+20H], 8                 
        xor     ecx, ecx                               
        mov     edx, 2                                 
        mov     r8d, 4                                 
        mov     r9d, 6                                 
        call    formula_calc                           
        xor     ecx, ecx                               
        mov     edx, eax                               
        call    formula_GetResult                       
        xor     ecx, ecx                               
        call    ExitProcess                             
        add     rsp, 56                                 
        ret                                             
mainCRTStartup ENDP

--- End code ---

Vortex:
Hi Timo,

I updated my code to remove the name mangling :


--- Code: ---calc PROTO :QWORD,:QWORD,:QWORD,:QWORD,:QWORD,:QWORD

GetResult PROTO :QWORD,:QWORD

ExitProcess PROTO :QWORD

.code

start PROC PARMAREA=6*QWORD

;   rcx ->  this pointer

    invoke  calc,rcx,2,4,6,8,10

;   rcx ->  this pointer

    invoke  GetResult,rcx,rax

    invoke  ExitProcess,0

start ENDP

END start
--- End code ---

Linking the object modules :


--- Code: ---\PellesC\bin\polink /SUBSYSTEM:CONSOLE /LARGEADDRESSAWARE /LIBPATH:\PellesC\lib\Win64 /ALTERNATENAME:GetResult=?GetResult@formula@@QEAAXH@Z /ALTERNATENAME:calc=?calc@formula@@QEAAHHHHHH@Z CallCppFunc.obj Class.obj kernel32.lib msvcrt.lib
--- End code ---

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