How can I enable my 32-bit Delphi application to use 4gb of memory on 64-bit windows (via Wow64.exe)?

Question

According to this MSDN page:

WOW64 enables 32-bit applications to take advantage of the 64-bit kernel. Therefore, 32-bit applications can use a

Answer 1

See this CodeCentral article: Using more than 3 GB memory in a 32 bit Delphi program.

In modern Delphi versions just add compiler directive to the dpr: {$SetPEFlags IMAGE_FILE_LARGE_ADDRESS_AWARE}

Answer 2

If you do this, make sure to use FastMM because it supports > 2GB pointers. Earlier Delphi memory managers won't work well as Barry Kelly already described.

Answer 3

Use the linker directive $SetPEFlags:

{$SetPEFlags IMAGE_FILE_LARGE_ADDRESS_AWARE}

The IMAGE_FILE_LARGE_ADDRESS_AWARE constant is defined in Windows.pas. I don't remember which Delphi version first included it, though.

In Delphi 2007, you'll find SetPEFlags documented in "PE (portable executable) header flags (Delphi)".

Some useful IMAGE_FILE_HEADER flags:

• {$SetPEFlags IMAGE_FILE_LARGE_ADDRESS_AWARE} //$0020

  Application can handle addresses larger than 2 GB.

• {$SetPEFlags IMAGE_FILE_NET_RUN_FROM_SWAP} //$0800

  If the image is on the network, copy it to and run it from the swap file.

• {$SetPEFlags IMAGE_FILE_REMOVABLE_RUN_FROM_SWAP} //$0400

  If the image is on removable media, copy it to and run it from the swap file.

Some IMAGE_FILE_HEADER flags:

• {$SetPEOptFlags IMAGE_DLLCHARACTERISTICS_NX_COMPAT} //$0100

  The image is compatible with data execution prevention (DEP).

• {$SetPEOptFlags IMAGE_DLLCHARACTERISTICS_DYNAMIC_BASE} //$0040

  The DLL can be relocated at load time. (aka ASLR - Address Space Layout Randomization)

• {$SetPEOptFlags IMAGE_DLLCHARACTERISTICS_TERMINAL_SERVER_AWARE} //$8000

  The image is terminal server aware.

Answer 4

Note that there are assumptions baked into the compiler and RTL that pointers, interpreted as signed 32-bit integers, will never be negative. For example, the compiler will not permit creating a data structure greater than 2GB in size, and certain boundary checks in the RTL assume that e.g. Index + Count < 0 meant the addition overflowed, where Index may be an index into a byte array. Other problems may crop up in the memory manager.

Test well and proceed at your own risk.