C++ visual studio inline assembly how do I call an address

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The problem that i'm having is that I'm trying to do the following in Inline Asm

asd is the address

"call asd"

When viewing it in a hex editor it writes "call dword ptr asd"

I'm quite lost

What I have tried:

I've tried using two things so far in the inline assembly

"call offset asd"

"call asd"

Neither work, I'm missing something and I cant figure out how to go about this

Posted 6-Oct-18 8:22am

Member 14004556

Updated 6-Oct-18 15:24pm

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Rick York · Answer 1 · 2018-10-06T15:24:00

When I am uncertain about the assembly code instructions, I write a snippet of code in C or C++ and then look at the assembly code listing. I did that with this. This code has a simple function and a pointer to it which is called. Here is the assembly code listing :

C++

?DoFunctionTest@@YAXXZ PROC				; DoFunctionTest
; 237  : {

$LN3:
	push	rdi
	sub	rsp, 64					; 00000040H
	mov	rdi, rsp
	mov	ecx, 16
	mov	eax, -858993460				; ccccccccH
	rep stosd

; 238  : 	double x = 16.612;

	movsd	xmm0, QWORD PTR __real@40309cac083126e9
	movsd	QWORD PTR x$[rsp], xmm0

; 239  : 	dblfunc df = factor; // factor is the function, df is a pointer to it

	lea	rax, OFFSET FLAT:?fac@@YANN@Z		; fac
	mov	QWORD PTR df$[rsp], rax

; 240  : 	double result = ( *df )( x );  // call the function - deref the pointer

	movsd	xmm0, QWORD PTR x$[rsp]
	call	QWORD PTR df$[rsp]              ; the actual function call is here
	movsd	QWORD PTR result$[rsp], xmm0

; 241  : 	trace( _T( "DoFunctionTest() - result is %.3f\n" ), result );

	movsd	xmm1, QWORD PTR result$[rsp]
	movq	rdx, xmm1
	lea	rcx, OFFSET FLAT:$SG255887
	call	?trace@@YA_NPEB_WZZ			; trace

; 242  : }

That was the assembly code in debug Unicode 64-bit mode for this code:

C++

double fac( double x )
{
	return 1.0 + x;
}

typedef double ( *dblfunc )( double x );

void DoFunctionTest()
{
	double x = 16.612;
	dblfunc df = fac;
	double result = ( *df )( x );
	trace( _T( "DoFunctionTest() - result is %.3f\n" ), result );
}