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The hidden danger of forgetting to specify %SystemRoot% in a custom environment block

When spawning a process using CreateProcess and friends, the child process usually inherits the environment (i.e. all environment variables) of the spawning process. Of course, this behavior can be overridden by creating a custom environment block and passing it to the lpEnvironment parameter of CreateProcess. While the MSDN documentation on CreateProcess does contain a remark saying that current directory information (=C: and friends) should be included in such a custom environment block, it does not mention the importance of SystemRoot. Continue »

Mixing 32 and 64-bit components in a single MSI

Definetely one my pet peeves about Windows Installer is how it deals with instruction set architectures (ISAs). Looking at Windows NT history, supported ISAs have come (amd64, IA-64) and gone (Alpha, PowerPC, MIPS) – yet most of the time, there was more than one ISA being officially supported. Having to ship binaries for multiple ISAs therefore always has been on the agenda for many ISVs. Needless to say, supporting multiple ISAs requires special consideration when developing setup packages and providing separate packages – one for each ISA – has become common practice to approach this. Continue »

RCW Reference Counting Rules != COM Reference Counting Rules

Avoiding COM object leaks in managed applications that make use of COM Interop can be a daunting task. While diligent tracking of COM object references and appropriate usage of Marshal.ReleaseComObject usually works fine, COM Interop is always good for surprises. Recently having been tracking down a COM object leak in a COM/.Net-Interop-centric application, I noticed that the CLR did not quite manage the reference count on my COM object as I expected it to do – more precisely, it incremented the referece count of a COM object when it was passed (from COM) as a method parameter to a callback implemented in . Continue »

Working Around TlbImp's Cleverness

TlbImp, the .Net tool to create Interop assemblies from COM type libraries, contains an optimization that presumably aims at making the consumption of the Interop assembly easier, but ultimately is a nuisance. Consider the following IDL code: import "oaidl.idl"; import "ocidl.idl"; [ uuid( a657ef35-fea1-40ad-86d8-bb7b6085a0a3 ), version( 1.0 ) ] library Test { [ object, uuid( 84b2f017-b8fe-4c2c-87b8-0587b4bf5507 ), version( 1.0 ), oleautomation ] interface IFoo : IUnknown { HRESULT Foo(); } [ object, uuid( 13d950d6-beb3-4dd3-957b-88b0e5eb5e3f ), version( 1. Continue »

Error Codes: Win32 vs. HRESULT vs. NTSTATUS

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There are three common error code formats used throughout Windows. In the kernel and native part, NTSTATUS is used exclusively. The Win32 API uses its own error codes (they do not really have a name, so I will refer to them as Win32 error codes) and COM uses HRESULTs – though the separation is not always so sharp, e.g. the safe string functions (StringCch* and friends) also return HRESULTs although they do not belong to COM. Continue »

Determining the apartment of a thread

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There are situations in which it would be convenient to list which apartment the threads of a process belong to. In case of managed debugging, the !threads command provided by SOS gives this info: PreEmptive GC Alloc Lock ID ThreadOBJ State GC Context Domain Count APT Exception 0 688 00149528 6020 Enabled 00000000:00000000 00159e68 0 STA 1 f70 00165548 b220 Enabled 00000000:00000000 00159e68 0 MTA (Finalizer) In case of unmanaged debugging, however, no such command exists (at least to my knowledge). Continue »