« Posts under WoW64

wow64ext v1.0.0.8

New version of wow64ext library is available for download:
or if someone prefer github:


  • Fixed elusive bug that appears only on AMD cpus
  • Removed VS CRT dependencies – dll size shrank to 9kB (previously 41kB)
  • Added sanity checks, so x64 switch won’t run on x86 OS

»Read More

wow64ext v1.0.0.7

New version of wow64ext library is available for download:


  • All 64bit APIs are now properly setting last Win32 error, thanks goes to Dreg (http://www.fr33project.org/) who implemented this feature.

This is actually unexpected benefit from hosting wow64ext on github (google code is dead, long live github), so if some of you want to add something to this library do not hesitate to do pull requests. I can’t promise that I’ll accept everything, but at least you may try :) Here is the address:

WoW64 internals: Unexpected behaviour of NtQueryDirectoryObject

Some time ago I was writing a small class that was supposed to list items from windows objects directory (like WinObj from Sysinternals). Given the fact that there are a lot of examples out there on the internet, it seemed like an easy task. I’ve started coding it without reading any documentation, except required functions definitions:

NTSTATUS WINAPI NtOpenDirectoryObject(
  _Out_ PHANDLE            DirectoryHandle,
  _In_  ACCESS_MASK        DesiredAccess,
  _In_  POBJECT_ATTRIBUTES ObjectAttributes
NTSTATUS WINAPI NtQueryDirectoryObject(
  _In_      HANDLE  DirectoryHandle,
  _Out_opt_ PVOID   Buffer,
  _In_      ULONG   Length,
  _In_      BOOLEAN ReturnSingleEntry,
  _In_      BOOLEAN RestartScan,
  _Inout_   PULONG  Context,
  _Out_opt_ PULONG  ReturnLength

»Read More

wow64ext v1.0.0.6

New version of wow64ext library is available for download:


  • Bugfix for improperly aligned stack. It was aligned to 8, and it was failing when some x64 SSE code was executed as it needs 0x10 alignment. Thanks goes to Vlad, who pointed it out in some recent comment under previous release: http://blog.rewolf.pl/blog/?p=1097#comment-51893. This bug was present since the first version of the library, thankfully now it’s gone.

wow64ext v1.0.0.5

New version of wow64ext library is available for download:


  • Added VirtualProtectEx64
  • Bugfix for ReadProcessMemory64 / WriteProcessMemory64 lpNumberOfBytesRead / lpNumberOfBytesWritten is declared as SIZE_T pointer. SIZE_T on x64 platforms is 64bit value, but wow64ext library is 32bit, so SIZE_T will be 32bit. Passing this pointer directly to the x64 version of NtReadVirtualMemory / NtWriteVirtualMemory would lead to a buffer overflow. To keep backward compatibility, I’ve introduced intermediate DWORD64 value that is used internally by ReadProcessMemory64 / WriteProcessMemory64, result is cropped to 32bit value, but it shouldn’t be a problem most cases.
    Link to described fix:

wow64ext v1.0.0.4 – bugfix release

Bugfix release, there was a problem with GetModuleHandle64 in the previous version of the library (only v1.0.0.3 was affected). Basically I’ve failed at InLoadOrderModuleList iteration and I was skipping the last element, which is (usually) wow64cpu.dll.

Link to library hosted on google code: http://code.google.com/p/rewolf-wow64ext/
Direct link to zip package: http://rewolf-wow64ext.googlecode.com/files/rewolf.wow64ext.v1.0.0.4.zip

wow64ext finally compatible with Windows 8

I’ve some good news for everyone who was complaining that wow64ext library doesn’t work on Windows 8. I’ve researched this topic a bit, and I’ve released fixed version of the library. Problem was very simple, but it couldn’t be fixed with just one line of code. On Windows 8/8.1 x64 version of NTDLL is loaded at address above 4GB, it wasn’t the case on previous versions of Windows, as x64 NTDLL was always loaded below 4GB. Also some of the system structures are mapped above 4GB (PEB_LDR_DATA64). To fix all the issues I had to introduce new memcpy-like function that can copy data from addresses above 4GB to addresses that are accessible by the standard x86 code. I’ve also fixed problem with case-sensitive GetModuleHandle64 that popped up recently. Below you can find direct link to the updated library:

Link to library hosted on google code: http://code.google.com/p/rewolf-wow64ext/
Direct link to zip package: http://rewolf-wow64ext.googlecode.com/files/rewolf.wow64ext.v1.0.0.3.zip

WoW64 internals: Tale of GetSystemFileCacheSize

Few days ago someone asked me if I can somehow add GetSystemFileCacheSize to wow64ext library. I’ve researched this topic a bit and the final answer is no, because it is not necessary. In today post I’ll try to describe internals of GetSystemFileCacheSize function and its limitations, I’ll also show the different way of obtaining the same information as original GetSystemFileCacheSize.

»Read More

Debugging ring 3 part of PE/PE+ loader

Someone may ask what is the purpose of debugging PE loader, here are a few reasons:

  • checking why executable is not loaded properly (imports, TLS, other initialization related issues)
  • looking for some hidden features (e.g. LdrpCheckNXCompatibility)
  • plain curiosity

Of course debugging ring 3 part of PE/PE+ loader can reveal only part of the truth, for the second part (or rather first part if I want to be strict) there is MiCreateImageFileMap function inside ntoskrnl (source code of this function can be found in Windows Research Kernel: \base\ntos\mm\creasect.c, it is a bit old, but most of the stuff hasn’t changed much). In this short article I’ll cover only x86 and x64 of ring 3 part.

»Read More

wow64ext library update 2

There is available new update for wow64ext library, I’ve added two new functions:

  • SetThreadContext64()
  • GetThreadContext64()

There is also definition of _CONTEXT64 structure that is used by those functions. Sample usage:

        _CONTEXT64 ctx = { 0 };
        ctx.ContextFlags = CONTEXT64_ALL;
        GetThreadContext64(GetCurrentThread(), &ctx);
        printf("rsp: %016I64X\n", ctx.Rsp);
        printf("rip: %016I64X\n", ctx.Rip);
        printf("r8 : %016I64X\n", ctx.R8);
        printf("r9 : %016I64X\n", ctx.R9);
        printf("r12: %016I64X\n", ctx.R12);

Link to library hosted on google code: http://code.google.com/p/rewolf-wow64ext/
Direct link to zip package: https://rewolf-wow64ext.googlecode.com/files/rewolf.wow64ext.v1.0.2.zip