Question

Using either Delphi 2007+ or Lazarus(Win64) I’m looking for a way to determine if a dll is compiled as x64 or x86?

Answer 1

You should read and parse PE header.

Like this:

function Isx64(const Strm: TStream): Boolean;
const
  IMAGE_FILE_MACHINE_I386     = $014c; // Intel x86
  IMAGE_FILE_MACHINE_IA64     = $0200; // Intel Itanium Processor Family (IPF)
  IMAGE_FILE_MACHINE_AMD64    = $8664; // x64 (AMD64 or EM64T)
  // You'll unlikely encounter the things below:
  IMAGE_FILE_MACHINE_R3000_BE = $160;  // MIPS big-endian
  IMAGE_FILE_MACHINE_R3000    = $162;  // MIPS little-endian, 0x160 big-endian
  IMAGE_FILE_MACHINE_R4000    = $166;  // MIPS little-endian
  IMAGE_FILE_MACHINE_R10000   = $168;  // MIPS little-endian
  IMAGE_FILE_MACHINE_ALPHA    = $184;  // Alpha_AXP }
  IMAGE_FILE_MACHINE_POWERPC  = $1F0;  // IBM PowerPC Little-Endian
var
  Header: TImageDosHeader;
  ImageNtHeaders: TImageNtHeaders;
begin
  Strm.ReadBuffer(Header, SizeOf(Header));
  if (Header.e_magic <> IMAGE_DOS_SIGNATURE) or
     (Header._lfanew = 0) then
    raise Exception.Create('Invalid executable');
  Strm.Position := Header._lfanew;

  Strm.ReadBuffer(ImageNtHeaders, SizeOf(ImageNtHeaders));
  if ImageNtHeaders.Signature <> IMAGE_NT_SIGNATURE then
    raise Exception.Create('Invalid executable');

  Result := ImageNtHeaders.FileHeader.Machine <> IMAGE_FILE_MACHINE_I386;
end;