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 larger number of kernel handles and window handles. However, 32-bit applications may not be able to create as many threads under WOW64 as they can when running natively on x86-based systems because WOW64 allocates an additional 64-bit stack (usually 512 KB) for each thread. In addition, some amount of address space is reserved for WOW64 itself and the data structures it uses. The amount reserved depends on the processor; more is reserved on the Intel Itanium than on the x64 processor.

If the application has the IMAGE_FILE_LARGE_ADDRESS_AWARE flag set in the image header, each 32-bit application receives 4 GB of virtual address space in the WOW64 environment. If the IMAGE_FILE_LARGE_ADDRESS_AWARE flag is not set, each 32-bit application receives 2 GB of virtual address space in the WOW64 environment.

How do I effectively set the IMAGE_FILE_LARGE_ADDRESS_AWARE flag in my Delphi 2007 application so that I can make my 32-bit application Wow64 aware and address up to a full 4GB of memory?

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

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 3

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.

Answer 4

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.