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Index > Macroinstructions > 64bit fastcall string literals and vararg

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johnsa



Joined: 31 Jul 2013
Posts: 1
johnsa
Hey,

I've recently moved to using fasm from masm etc.

How would I go about using 64bit fastcall macro and support some form of string literals and vararg ?

for example:

Code:
fastcall myFunction, "a message"

; (normally in masm and jwasm I would use:

invoke myFunction, CStr("a message")
    


And how would a vararg work?

Code:

; I'm used to

myFunction proc frame uses rsi arguments:VARARG
ret
endp

; and then rcx = count and arguments are on the stack 

    
[/code]
Post 28 Feb 2015, 23:33
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17474
Location: In your JS exploiting you and your system
revolution
johnsa wrote:
How would I go about using 64bit fastcall macro and support some form of string literals and vararg ?
Code:
include 'win64ax.inc'

.code

proc start
        fastcall func,'string1','string2'
        fastcall ExitProcess,0
endp

proc func arg1,arg2,arg3,arg4,more_args
        mov     [arg1],rcx
        mov     [arg2],rdx
        mov     [arg3],r8
        mov     [arg4],r9
        ;...
        ret
endp

.end start    
johnsa wrote:
... and then rcx = count and arguments are on the stack
fastcall does not support using rcx as the argument count because the first argument is placed in rcx. You can of course modify the fasm macros to place the count in rcx (or rax, or whatever) but it is then no longer a fastcall under the normal definition.
Post 01 Mar 2015, 01:43
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