Delphi子过程参数传递

默认调用方式Register，传递参数的顺序前三个为al,dl,cl / ax,dx,cx / eax,edx,ecx分别对应一个字节，两个字节，四个字节，当参数>3个时，多出的参数入栈，所以第四个参数的地址为[esp+8],第五个参数的地址为[esp+12]，[esp+4]至[esp+0]这四个字是函数的返回地址。以上针对类以外的子过程，在类里面定义的过程参数传递有所改变，主要改变为eax保存了类的首地址即：self。

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    function _AddFunc(pa,pb,pc,pd,pe:Integer):Integer;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

function TForm1._AddFunc(pa, pb, pc, pd, pe: Integer): Integer;
asm
  xor eax,eax
  add eax,edx
  add eax,ecx
  add eax,[esp+8]
  add eax,[esp+12]
  add eax,[esp+16]
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  iSum: Integer;
begin
  iSum := _AddFunc(10,20,30,40,50);
  ShowMessageFmt('Integer Sum:%d',[iSum]);
end;

function addFunc(pa,pb,pc,pd: Byte):Byte;overload;assembler;
asm
  add al,dl
  add al,cl
  add al,[esp+8]
end;

function addFunc(pa,pb,pc,pd: Word):Word;overload;assembler;
asm
  add ax,dx
  add ax,cx
  add ax,[esp+8]
end;

function addFunc(pa,pb,pc,pd: Integer):Integer;overload;assembler;
asm
  add eax,edx
  add eax,ecx
  add eax,[esp+8]
end;

function addFunc(pa,pb,pc,pd,pe: Integer):Integer;overload;assembler;
asm
  add eax,edx
  add eax,ecx
  add eax,[esp+8]
  add eax,[esp+12]
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  bSum: Byte;
  wSum: Word;
  iSum: Integer;
begin
  bSum := addFunc(1,2,3,4);
  wSum := addFunc(3,4,5,6);
  iSum := addFunc(10,20,30,40,50);
  ShowMessageFmt('Byte Sum:%d',[bSum]);
  ShowMessageFmt('Word Sum:%d',[wSum]);
  ShowMessageFmt('Integer Sum:%d',[iSum]);
end;

function addFuncNew(pa,pb,pc,pd,pe: Integer):Integer;assembler;
asm
  add eax,edx
  add eax,ecx
  add eax,[esp+8]
  add eax,[esp+12]
end;

procedure TForm1.Button3Click(Sender: TObject);
asm
  push ebp
  mov ebp,esp
  add esp,-16
  mov eax,10
  mov edx,20
  mov ecx,30
  push 40 //esp := esp + 4
  push 50 //esp := esp + 4
  call addFuncNew
  lea edx,[esp+4] //4,8 ok, 12:error
  call system.IntToStr
  mov eax,[esp+4]
  call showMessage
  add esp,16
  mov esp,ebp
  pop ebp
end;

end.