Pinvokestackimbalance - How to Fix This or Turn It Off

pinvokestackimbalance -- how can I fix this or turn it off?

First, understand that the code is wrong (and always has been). The "pInvokeStackImbalance" is not an exception per se, but a managed debugging assistant. It was off by default in VS2008, but a lot of people did not turn it on, so it's on by default in VS2010. The MDA does not run in Release mode, so it won't trigger if you build for release.

In your case, the calling convention is incorrect. DllImport defaults to CallingConvention.WinApi, which is identical to CallingConvention.StdCall for x86 desktop code. It should be CallingConvention.Cdecl.

This can be done by editing the line [DllImport("ImageOperations.dll")] to be:

[DllImport("ImageOperations.dll", CallingConvention = CallingConvention.Cdecl)]

For more information, see this MSDN reference

pInvokeStackImbalance MDA Warning and how to turn it off or fix it

This MDA raised to tell you that you have a problem with parameters type you are using for PInvoke call. Generally, it is very bad idea to turn it off since it warns about problem in your code and imbalanced stack leads to errors (sometimes hard to find) in future.

Usually, common mistake is selected matching for unmanaged type with managed one.

In your case, original defininition (I take a look to zlib125.zip):

ZEXTERN int ZEXPORT compress2 OF((Bytef *dest,   uLongf *destLen,
                                  const Bytef *source, uLong sourceLen,
                                  int level)); 

which can be traslated to if library was compiled with 64-bit support for unsigned long:

static int compress2(
    byte[] dest,
    ref ulong destLength,
    byte[] source,
    ulong sourceLength,
    int level)

Ensure ZLibQualityenumeration is based on int. Probably, your error is usage int instead of ulong for both lengths.

As stated David Heffernan there are plenty other reasons to fail to find exact one give us link to library actually used for development if you still want to know.

• traditional compilation original library with Visual C++ will result you get library with 32-bit support only, so original definition you provided in question is valid unless ZLibQuality enumeration is not int based

• maybe you try to use library compiled for other calling convention such as cdecl instead of stdcall

• maybe you try to use modified library where compress2 function takes additional parameters.

We can find whats wrong when we can see exact library you are using.

long or unsigned long usually 32-bit under Windows and mapped to int or uint respectively. Since you have troubles with original declaration I assumed that maybe you are using specific library with 64-bit support. Thanks to David Heffernan to point me makes my notice clearly.

You can use folowing resourses as reference:

• A wiki for .NET developers - PInvoke.net is primarily a wiki, allowing developers to find, edit and add PInvoke* signatures, user-defined types, and any other information related to calling Win32 and other unmanaged APIs from managed code

• PInvoke Interop Assistant

/Offtopic:

Why do you use you own implementation with self bindings to library? You can use:

• DotNetZip - Zip and Unzip in C#, VB, any .NET language - DotNetZip is an easy-to-use, FAST, FREE class library and toolset for manipulating zip files or folders. Zip and Unzip is easy: with DotNetZip, .NET applications written in VB, C# - any .NET language - can easily create, read, extract, or update zip files. For Mono or MS .NET.

• or ready to use 7-zip bindings: SevenZipSharp - Managed 7-zip library written in C# that provides data (self-)extraction and compression (all 7-zip formats are supported). It wraps 7z.dll or any compatible one and makes use of LZMA SDK.

Why do I get PInvokeStackImbalance was detected for this simple example?

You need to instead use either

[DllImport("CommonNativeLib.dll", CallingConvention = CallingConvention.Cdecl)]

or

extern "C" __declspec(dllexport) int __stdcall Add(int a, int b) ...

because regular C functions work differently than the Windows API functions; their "calling conventions" are different, meaning how they pass around parameters is different. (This was hinted at in the error.)

Managed Debugging Assistant 'PInvokeStackImbalance' has detected a... on trivial method

There are a very large number of mistakes here. The immediate problem is here:

[DllImport("PascalBall.dll", EntryPoint = "TimTam", CallingConvention = CallingConvention.Cdecl)]
public static extern void OneTwoC(ref int a, ref int b);

[DllImport("PascalBall.dll", EntryPoint = "TimTam", CallingConvention = CallingConvention.StdCall)]
public static extern void OneTwoS(ref int a, ref int b);

Why are you specifying EntryPoint = "TimTam"? That function is not the one you are trying to import and has an incompatible signature. Hence the stack imbalance error.

You need to export OneTwoS and OneTwoC by adding them to the Delphi exports clause. And you need to import these functions in the C# by removing the erroneous EntryPoint specification.

You functions using strings are wrong too and can't be fixed without changing both sides of the code. The simple fix is to use WideString parameters in Delphi, var parameters. Map that to ref string in C#, marshaled as UnmanagedType.BStr. The answer you linked to in comments shows you how: https://stackoverflow.com/a/26043567/495455

PinvokeStackImbalance error (C#)

    public int SendMail(..., long smtpPortNo);

It is excessively unlikely that the last argument is correct. Makes no sense at all to store a value that must be less than 65536 in a 64-bit long argument. It surely should be int instead. A classic Visual Basic accident, versions before VB.NET used Long to declare a 32-bit integer.

Why this didn't generate the diagnostic in 3.5 is hard to guess, it certainly should. Maybe you just never ran it with a debugger attached with the MDA enabled. Stack corruption caused by getting the declaration wrong has a habit of healing itself so it doesn't necessarily have to bomb at runtime. Still, a very, very unhealthy problem that can cause pretty random code execution.

Three basic things you can do about it. On top of the list with bells on is to use a telephone, you want the author of this library to fix his bug. Next is to try to flip the ignore bit and turn the MDA off: Debug > Exceptions > Managed Debugging Assistants, untick "PInvokeStackImbalance". And I probably ought to mention the new 4.0 config file option, <NetFx40_PInvokeStackResilience>, hesitantly.

But, really, that telephone must be your real fix.

How to fix a Pinvoke stack imbalance detected error

The error that comes is this one: PInvoke stack imbalance detected.

Just a bit of background behind what you see, Ria's answer will solve your problem. This is not actually an error, it is a warning that's produced by an MDA. A Managed Debugging Assistant, it is extra code that's added to the CLR, the framework and the debugger to keep an eye on unintended runtime problems and activated when you run with a debugger. You can have a look at what MDAs are available, use Debug + Exceptions and expand the "Managed Debugging Assistants" node to see them. A lot of them are disabled by default because they tend to be noisy or tend to generate false warnings or already generate an exception later. Do note that the pInvokeStackImbalance MDA isn't actually listed there, it is special because it can't be turned off.

The complete list of MDAs is documented here. The description of pInvokeStackImbalance contains a decent description of the cause of the problem it detects:

The managed signature of the platform invoke call might not match the unmanaged signature of the method being called. This mismatch can be caused by the managed signature not declaring the correct number of parameters or not specifying the appropriate size for the parameters. The MDA can also activate because the calling convention, possibly specified by the DllImportAttribute attribute, does not match the unmanaged calling convention.

I highlighted the true reason in your case, your lParam argument has the wrong type. The wParam type is wrong too but happens to have the right size by accident. Those kind of accidents tend to byte when your code runs on a 64-bit operating system.

Although this is only a warning, and your code appears to be running just fine when you ignore it and continue running, a stack imbalance is a very serious kind of runtime problem. The failure mode is unpredictable, it might run just fine in the Debug build but bomb your program with an inscrutable exception in the Release build. The specific problem here is that you push too much data on the stack when you call the method and Windows doesn't pop enough off the stack. Which can bomb your program with this site's name when you call it often enough. The problem tends to be hidden because returning from a C# method re-balances the stack. All bets are off when in Release mode the jitter optimizer inlines the method. Which it only does when you don't have a debugger attached, the worst kind of bug to try to diagnose.

Finding the right pinvoke declaration is not particularly easy. There is more than one way to declare them and you'll often find intentional "lies" about a declaration to make a function easier to pinvoke. The pinvoke.net site is a fairly decent source, albeit that it tends to over-specify declarations. Like in Ria's example, the [return:] attribute is unnecessary since that is already the default marshaling for a bool. And HandleRef doesn't make much sense when you don't own the window handle. But it will work just fine. Another fairly decent source is the Pinvoke Interop Assistant, a tool you can find here. It produces auto-generated declarations, they are not pretty.

Last but not least, you can't use PostMessage to reliably poke keystrokes into the window of another process. You'll run into trouble when you need the keyboard state of the process to be accurate, particularly the Shift, Alt and Ctrl keys. And dead keys like Alt+Gr present on keyboards with a different layout, particularly for languages that have a lot of diacritics or a large alphabet. To poke typing keys you should favor WM_CHAR instead.

DLLImport attribute PInvokeStackImbalance error

I can see a few problems here.

• In C++ on Windows, long is 32 bit. So the baud parameter in your p/invoke should be Integer.
• The string parameter serialNumber is presumably a C string. That is pointer to null-terminated string. That would be ByVal serialNumber As String in the p/invoke.
• Finally the calling convention. As written, it would seem that the unmanaged code uses the cdecl calling convention. Your p/invoke uses stdcall. It is possible I suppose that the calling convention of the unmanaged code is in fact stdcall, and the documentation you have included omits that. A read of the library's header file would clear that up.
• I think it unlikely that the function returns errors by calling SetLastError.

So, in summary, the p/invoke should be

<DllImport("armdll32.dll", CallingConvention=CallingConvention.Cdecl, _
    CharSet:=CharSet.Ansi)>
Public Shared Function ArmConnect( _
    ByVal port As Integer, _
    ByVal baud As Integer, _
    ByVal serialNumber As String _
) As Integer
End Function

or

<DllImport("armdll32.dll", CallingConvention=CallingConvention.Stdcall, _
    CharSet:=CharSet.Ansi)>
Public Shared Function ArmConnect( _
    ByVal port As Integer, _
    ByVal baud As Integer, _
    ByVal serialNumber As String _
) As Integer
End Function

.Rdlc Report in MVC project - Managed Debugging Assistant 'PInvokeStackImbalance'

According to this answer, PInvokeStackImbalance is more of a "debugging assistant" than an exception. So...

In my case, as it did not prevent the report from being rendered, I just disabled this exception when debugging my project (see Tell the debugger to continue on user-unhandled exceptions). This did the trick for me.

PInvokeStackImbalance was detected from HDFDotNet 1.8.7

Yes, calling a stdcall function as cdecl or the other way round causes a stack imbalance. The main difference between these conventions is that with cdecl the caller is responsible for removing the arguments from the stack, with stdcall the callee is responsible.

I guess in release mode you have the same bug. But you don't get the error because some runtime checks are disabled. A native program would crash in most cases where you use the wrong calling convention, but it seems like the .net interop code has a more robust stack handling that masks this problem.

---

Related Topics