Many thanks, Andrew. I intend to apply this to my old programs in 32
bit Windows. I'll tell you about the outcome.
Below you will see a console application for testing your suggestions
or better my understanding of them. The results are (in Windows XP 64
bits Pro):
1. When Data Execution Prevention (DEP) is enforced, the program
fails.
2. When DEP is enforced only for essential Windows programs, the
program functions (that is, it writes the value of pi). But if
one uncomments the commented line of code, that is makes
codeFunction:= '',
the program fails.
What may be happening here?
Many thanks
--
montesin at uv dot es
{--------------begins code for console app------------------}
program Test_VirtualAlloc;
{$APPTYPE CONSOLE}
uses
SysUtils, Types, Windows;
type
PCodeBlock= ^CodeBlock;
CodeBlock = record
size: DWord;
code: Pointer;
end;
RealFunction = function(const X : array of Extended) : Extended;
TOpCodeFunctionExtended = class(TObject)
private
functionCode : AnsiString; {the function opCode sequence}
public
F : function(const X : array of Extended) : Extended;
FBlock: PCodeBlock;
constructor Create;
destructor Destroy; override;
end;
var
theF: TOpCodeFunctionExtended;
rslt: Extended;
linetxt: AnsiString;
constructor TOpCodeFunctionExtended.Create;
var
len: Integer;
begin
inherited;
{execution of this puts pi in the register st(0) of FPU}
functionCode:= #$55 + {push ebp}
#$8B#$EC + {mov ebp, esp}
#$D9#$EB + {fldpi}
#$C9 + {leave}
#$C3; {ret}
len:= Length(functionCode);
FBlock:= VirtualAlloc(nil, len + SizeOf(codeBlock), MEM_COMMIT,
PAGE_EXECUTE_READWRITE);
Move(functionCode, PChar(FBlock^.code), len);
FBlock.size:= len;
@F := FBlock^.code; {assignation of code to the function}
//functionCode:= ''; {if this is uncommented, program fails}
end;
destructor TOpCodeFunctionExtended.Destroy;
begin
if FBlock <> nil then begin
VirtualFree(FBlock, 0, MEM_RELEASE);
FBlock:= nil;
end;
theF.Free;
inherited
end;
begin
theF:= TOpCodeFunctionExtended.Create;
Writeln('Enter a character. For exiting, enter an ''x''');
Writeln;
try
repeat
readln(linetxt);
if linetxt <> 'x' then begin
rslt:= theF.F([]);
writeln(FloatToStrF(rslt, ffFixed, 18, 18));
end;
until linetxt = 'x';
except on exception do
;
end;
end.
{--------------ends code for console app------------------}
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