Delphi 实现C语言函数调用

在X86下，C语言函数调用，使将参数从右到左压入堆栈，栈指针减小，最后一个参数压入后，栈指针指向最后一个参数

因此我们可以通过增加栈指针，读取所有的参数，X86CPU的堆栈是4字节对齐，也就是说字节性或者字型参数都是压入4

字节。

type  
  TArgPtr =record
  private
    FArgPtr: PByte;classfunction Align(Ptr: Pointer; Align: Integer): Pointer; static;
  public
    constructor Create(LastArg: Pointer; Size: Integer);
　　// Read bytes, signed words etc. using Int32
    // Make an unsigned version if necessary.
    function ReadInt32: Integer;
    // Exact floating-point semantics depend on C compiler.
    // Delphi compiler passes Extended as 10-byte float; most C
    // compilers pass all floating-point values as 8-byte floats.
    function ReadDouble: Double;
    function ReadExtended: Extended;
    function ReadPChar: PChar;
    procedure ReadArg(var Arg; Size: Integer);
  end;

constructor TArgPtr.Create(LastArg: Pointer; Size: Integer);
begin
  FArgPtr := LastArg;// 32-bit x86 stack is generally 4-byte aligned
  FArgPtr := Align(FArgPtr + Size,4);
end;
classfunction TArgPtr.Align(Ptr: Pointer; Align: Integer): Pointer;
begin
  Integer(Result):=(Integer(Ptr)+ Align -1)and not(Align -1);
end;
function TArgPtr.ReadInt32: Integer;
begin
  ReadArg(Result, SizeOf(Integer));
end;
function TArgPtr.ReadDouble: Double;
begin
  ReadArg(Result, SizeOf(Double));
end;
function TArgPtr.ReadExtended: Extended;
begin
  ReadArg(Result, SizeOf(Extended));
end;
function TArgPtr.ReadPChar: PChar;
begin
  ReadArg(Result, SizeOf(PChar));
end;
procedure TArgPtr.ReadArg(var Arg; Size: Integer);
begin
  Move(FArgPtr^, Arg, Size);
  FArgPtr := Align(FArgPtr + Size,4);
end;
procedure Dump(const types:string); cdecl;
var
  ap: TArgPtr;
  cp: PChar;
begin
  cp := PChar(types);
  ap := TArgPtr.Create(@types, SizeOf(string));
　while True do
  begin
    case cp^ of
    #0:begin
        Writeln;
        Exit;
       end;
    'i': Write(ap.ReadInt32,' ');
    'd': Write(ap.ReadDouble,' ');
    'e': Write(ap.ReadExtended,' ');
    's': Write(ap.ReadPChar,' ');
    else
      Writeln('Unknown format');
      Exit;
    end;
    Inc(cp);
  end;
end;
type
  PDump =procedure(const types:string) cdecl varargs;
var
  MyDump: PDump;
function AsDouble(e: Extended): Double;
begin
  Result := e;
end;
function AsSingle(e: Extended): Single;
begin
  Result := e;
end;
procedure Go;
begin
  MyDump :=@Dump;

  MyDump('iii',10,20,30);
  MyDump('sss','foo','bar','baz');// Looks like Delphi passes Extended in byte-aligned// stack offset, very strange; thus this doesn't work.
  MyDump('e',2.0);// These two are more reliable.
  MyDump('d', AsDouble(2));// Singles passed as 8-byte floats.
  MyDump('d', AsSingle(2));
end;
begin
  Go;
end.