Gendarme Rules: Interoperability

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Gendarme’s interoperability rules are located in the Gendarme.Rules.Interoperability.dll assembly. Latest sources are available from git.

Table of contents

Rules

DelegatesPassedToNativeCodeMustIncludeExceptionHandlingRule

Every delegate which is passed to native code must include an exception block which spans the entire method and has a catch all handler.

Bad example:

public void NativeCallback ()
{
    Console.WriteLine ("{0}", 1);
}

Good example:

public void NativeCallback ()
{
    try {
        Console.WriteLine ("{0}", 1);
    }
    catch {
    }
}

Notes

  • This rule is available since Gendarme 2.6

DoNotAssumeIntPtrSizeRule

This rule checks for code which casts an IntPtr or UIntPtr into a 32-bit (or smaller) value. It will also check if memory read with the Marshal.ReadInt32and Marshal.ReadInt64 methods is being cast into an IntPtr or UIntPtr. IntPtr is generally used to reference a memory location and downcasting them to 32-bits will make the code fail on 64-bit CPUs.

Bad example (cast):

int ptr = dest.ToInt32 ();
for (int i = 0; i < 16; i++) {
    Marshal.StructureToPtr (this, (IntPtr)ptr, false);
    ptr += 4;
}

Bad example (Marshal.Read*):

// that won't work on 64 bits platforms
IntPtr p = (IntPtr) Marshal.ReadInt32 (p);

Good example (cast):

long ptr = dest.ToInt64 ();
for (int i = 0; i < 16; i++) {
    Marshal.StructureToPtr (this, (IntPtr) ptr, false);
    ptr += IntPtr.Size;
}

Good example (Marshal.Read*):

IntPtr p = (IntPtr) Marshal.ReadIntPtr (p);

Notes

  • This rule is available since Gendarme 2.0 but was named DoNotCastIntPtrToInt32Rule before 2.2

GetLastErrorMustBeCalledRightAfterPInvokeRule

This rule will fire if Marshal.GetLastWin32Error() is called, but is not called immediately after a P/Invoke. This is a problem because other methods, even managed methods, may overwrite the error code.

Bad example:

public void DestroyError ()
{
    MessageBeep (2);
    Console.WriteLine ("Beep");
    int error = Marshal.GetLastWin32Error ();
}

Good example:

public void GetError ()
{
    MessageBeep (2);
    int error = Marshal.GetLastWin32Error ();
    Console.WriteLine ("Beep");
}
 
public void DontUseGetLastError ()
{
    MessageBeep (2);
    Console.WriteLine ("Beep");
}

MarshalBooleansInPInvokeDeclarationsRule

This rule warns the developer if a [MarshalAs] attribute has not been specified for boolean parameters of a P/Invoke method. The size of boolean types varies across language (e.g. the C++ bool type is four bytes on some platforms and one byte on others). By default the CLR will marshal System.Booleanas a 32 bit value (UnmanagedType.Bool) like the Win32 API BOOLuses. But, for clarity, you should always specify the correct value.

Bad example:

// bad assuming the last parameter is a single byte being mapped to a bool
[DllImport ("liberty")]
private static extern bool Bad (bool b1, ref bool b2);

Good example:

[DllImport ("liberty")]
[return: MarshalAs (UnmanagedType.Bool)]
private static extern bool Good ([MarshalAs (UnmanagedType.Bool)] bool b1, [MarshalAs (UnmanagedType.U1)] ref bool b2);

MarshalStringsInPInvokeDeclarationsRule

This rule will fire if a P/Invoke method has System.String or System.Text.StringBuilder arguments, and the DllImportAttribute does not specify the CharSet, and the string arguments are not decorated with [MarshalAs]. This is important because the defaults are different on the various platforms. On Mono the default is to always use utf-8. On .NET the default is to use the ANSI CharSet which is the native encoding and will typically be some variant of ASCII or something like Shift-JIS. On Compact .NET the default is utf-16.

Bad example:

[DllImport ("coredll")]
static extern int SHCreateShortcut (StringBuilder szShortcut, StringBuilder szTarget);

Good examples:

[DllImport ("coredll", CharSet = CharSet.Auto)]
static extern int SHCreateShortcut (StringBuilder szShortcut, StringBuilder szTarget);
 
[DllImport ("coredll")]
static extern int SHCreateShortcut ([MarshalAs (UnmanagedType.LPTStr)] StringBuilder szShortcut,
[MarshalAs (UnmanagedType.LPTStr)] StringBuilder szTarget);

PInvokeShouldNotBeVisibleRule

This rule checks for PInvoke declaration methods that are visible outside their assembly.

Bad example:

[DllImport ("user32.dll")]
public static extern bool MessageBeep (UInt32 beepType);

Good example:

[DllImport ("user32.dll")]
internal static extern bool MessageBeep (UInt32 beepType);

UseManagedAlternativesToPInvokeRule

This rule will fire if an external (P/Invoke) method is called but a managed alternative is provided by the .NET framework.

Bad example:

[DllImport ("kernel32.dll")]
static extern void Sleep (uint dwMilliseconds);
 
public void WaitTwoSeconds ()
{
    Sleep (2000);
}

Good example:

public void WaitTwoSeconds ()
{
    System.Threading.Thread.Sleep (2000);
}

Feedback

Please report any documentation errors, typos or suggestions to the Gendarme Google Group. Thanks!