Prototype for a .NET managed assembly to expose a native export.
This work is inspired by work in the Xamarin, CoreRT, and DllExport projects.
Windows:
- Visual Studio 2015 or greater.
- The x86_64 version of the .NET runtime is the default install.
- In order to target x86, the x86 .NET runtime must be explicitly installed.
- Windows 10 SDK - Installed with Visual Studio.
- x86, x86_64, ARM64 compilation supported.
- The Visual Studio package containing the desired compiler architecture must have been installed.
macOS:
- clang compiler on the path.
- Current platform and environment paths dictate native compilation support.
Linux:
- clang compiler on the path.
- Current platform and environment paths dictate native compilation support.
-
The exported function must be marked
static
andpublic
. Note that enclosing class accessibility has no impact on exporting. -
Mark functions to export with
UnmanagedCallersOnlyAttribute
.public class Exports { [UnmanagedCallersOnlyAttribute(EntryPoint = "FancyName")] public static int MyExport(int a) { return a; } }
-
The manner in which native exports are exposed is largely a function of the compiler being used. On the Windows platform an option exists to provide a
.def
file that permits customization of native exports. Users can provide a path to a.def
file using theDnneWindowsExportsDef
MSBuild property. Note that if a.def
file is provided no user functions will be exported by default.
The native API is defined in src/platform/dnne.h
.
The DNNE_ASSEMBLY_NAME
must be set during compilation to indicate the name of the managed assembly to load. The assembly name should not include the extension. For example, if the managed assembly on disk is called ClassLib.dll
, the expected assembly name is ClassLib
.
The following defines are set based on the target OS platform:
DNNE_WINDOWS
DNNE_OSX
DNNE_LINUX
DNNE_FREEBSD
The generated source will need to be linked against the nethost
library as either a static lib (libnethost.[lib|a]
) or dynamic/shared library (nethost.lib
). If the latter linking is performed, the nethost.[dll|so|dylib]
will need to be deployed with the export binary or be on the path at run time.
The set_failure_callback()
function can be used prior to calling an export to set a callback in the event runtime load or export discovery fails.
Failure to load the runtime or find an export results in the native library calling abort()
. See FAQs for how this can be overridden.
The preload_runtime()
or try_preload_runtime()
functions can be used to preload the runtime. This may be desirable prior to calling an export to avoid the cost of loading the runtime during the first export dispatch.
-
Adorn the desired managed function with
UnmanagedCallersOnlyAttribute
.- Optionally set the
EntryPoint
property to indicate the name of the native export. See below for discussion of influence by calling convention. - If the
EntryPoint
property isnull
, the name of the mananged function is used. This default name will not include the namespace or class containing the function. - User supplied values in
EntryPoint
will not be modified or validated in any manner. This string will be consume by a C compiler and should therefore adhere to the C language's restrictions on function names. - On the x86 platform only, multiple calling conventions exist and these often influence exported symbols. For example, see MSVC C export decoration documentation. DNNE does not attempt to mitigate symbol decoration - even through
EntryPoint
. If the consuming application requires a specific export symbol and calling convention that is decorated in a customized way, it is recommended to manually compile the generated source - seeDnneBuildExports
- or if on Windows supply a.def
file - seeDnneWindowsExportsDef
. Typically, setting the calling convention tocdecl
for the export will address issues on any x86 platform.[UnmanagedCallersOnly(CallConvs = new []{typeof(System.Runtime.CompilerServices.CallConvCdecl)})]
- Optionally set the
-
Set the
<EnableDynamicLoading>true</EnableDynamicLoading>
property in the managed project containing the methods to export. This will produce a*.runtimeconfig.json
that is needed to activate the runtime during export dispatch.
The mapping of .NET types to their native representation is addressed by the concept of blittability. This approach however limits what can be expressed by the managed type signature when being called from an unmanaged context. For example, there is no way for DNNE to know how it should describe the following C struct in C# without being enriched with knowledge of how to construct marshallable types.
struct some_data
{
char* str;
union
{
short s;
double d;
} data;
};
The following attributes can be used to enable the above scenario. They must be defined by the project in order to be used - DNNE provides no assembly to reference. Refer to ExportingAssembly
for an example.
namespace DNNE
{
/// <summary>
/// Provide C code to be defined early in the generated C header file.
/// </summary>
/// <remarks>
/// This attribute is respected on an exported method declaration or on a parameter for the method.
/// The following header files will be included prior to the code being defined.
/// - stddef.h
/// - stdint.h
/// - dnne.h
/// </remarks>
internal class C99DeclCodeAttribute : System.Attribute
{
public C99DeclCodeAttribute(string code) { }
}
/// <summary>
/// Define the C type to be used.
/// </summary>
/// <remarks>
/// The level of indirection should be included in the supplied string.
/// </remarks>
internal class C99TypeAttribute : System.Attribute
{
public C99TypeAttribute(string code) { }
}
}
The above attributes can be used to manually define the native type mapping to be used in the export definition. For example:
public unsafe static class NativeExports
{
public struct Data
{
public int a;
public int b;
public int c;
}
[UnmanagedCallersOnly]
[DNNE.C99DeclCode("struct T{int a; int b; int c;};")]
public static int ReturnDataCMember([DNNE.C99Type("struct T")] Data d)
{
return d.c;
}
[UnmanagedCallersOnly]
public static int ReturnRefDataCMember([DNNE.C99Type("struct T*")] Data* d)
{
return d->c;
}
}
In addition to providing declaration code directly, users can also supply #include
directives for application specific headers. The DnneAdditionalIncludeDirectories
MSBuild property can be used to supply search paths in these cases. Consider the following use of the DNNE.C99DeclCode
attribute.
[DNNE.C99DeclCode("#include <fancyapp.h>")]
-
The DNNE NuPkg is published on NuGet.org, but can also be built locally.
-
Build the DNNE NuPkg locally by building
create_package.proj
.> dotnet build create_package.proj
-
-
Add the NuPkg to the target managed project.
-
See
DNNE.props
for the MSBuild properties used to configure the build process. -
If NuPkg was built locally, remember to update the project's
nuget.config
to point at the local location of the recently built DNNE NuPkg.
<ItemGroup> <PackageReference Include="DNNE" Version="1.*" /> </ItemGroup>
-
-
Build the managed project to generate the native binary. The native binary will have a
NE
suffix and the system extension for dynamic/shared native libraries (i.e.,.dll
,.so
,.dylib
).- The Runtime Identifier (RID) is used to target a specific SDK.
- For example, on Windows the
--runtime
flag or MSBuildRuntimeIdentifier
property can be used to targetwin-x86
orwin-x64
. - The name of the native binary can be supplied by setting the MSBuild property
DnneNativeBinaryName
. It is incumbent on the setter of this property that it doesn't collide with the name of the managed assembly. Practially, this only impacts the Windows platform because managed and native binaries share the same extension (i.e.,.dll
). - A header file containing the exports will be placed in the output directory. The
dnne.h
will also be placed in the output directory. - On Windows an import library (
.lib
) will be placed in the output directory.
-
Deploy the native binary, managed assembly and associated
*.json
files for consumption from a native process.- Although not technically needed, the exports header and import library (Windows only) can be deployed with the native binary to make consumption easier.
- Set the
DnneAddGeneratedBinaryToProject
MSBuild property totrue
in the project if it is desired to have the generated native binary flow with project references. Recall that the generated binary is bitness specific.
-
Run the dnne-gen tool on the managed assembly.
-
Take the generated source from
dnne-gen
and the DNNE platform source to compile a native binary with the desired native exports. See the Native API section for build details. -
Deploy the native binary, managed assembly and associated
*.json
files for consumption from a native process.
There are scenarios where updating UnmanagedCallersOnlyAttribute
may take time. In order to enable independent development and experimentation, the DNNE.ExportAttribute
is also respected. This type can be modified to suit one's needs and dnne-gen
updated to respect those changes at code gen time. The user should define the following in their assembly. They can then modify the attribute and dnne-gen
as needed.
namespace DNNE
{
internal class ExportAttribute : Attribute
{
public ExportAttribute() { }
public string EntryPoint { get; set; }
}
}
The calling convention of the export will be the default for the .NET runtime on that platform. See the description of CallingConvention.Winapi
.
Using DNNE.ExportAttribute
to export a method requires a Delegate
of the appropriate type and name to be at the same scope as the export. The naming convention is <METHODNAME>Delegate
. For example:
public class Exports
{
public delegate int MyExportDelegate(int a);
[DNNE.Export(EntryPoint = "FancyName")]
public static int MyExport(int a)
{
return a;
}
}
- I am not using one of the supported compilers and hitting an issue of missing
intptr_t
type, what can I do?- The C99 specification indicates several types like
intptr_t
anduintptr_t
are optional. It is recommended to override the computed type usingDNNE.C99TypeAttribute
. For example,[DNNE.C99Type("void*")]
can be used to override an instance whereintptr_t
is generated by DNNE.
- The C99 specification indicates several types like
- How can I use the same export name across platforms but with different implementations?
- The .NET platform provides
SupportedOSPlatformAttribute
andUnsupportedOSPlatformAttribute
which are fully supported by DNNE. All .NET supplied platform names are recognized. It is also possible to define your own usingC99DeclCodeAttribute
. SeeMiscExport.cs
for an example.
- The .NET platform provides
- The consuming application for my .NET assembly fails catastrophically if .NET is not installed. How can I improve this UX?
- For all non-recoverable scenarios, DNNE will call the standard C
abort()
function. This can be overridden by providing your owndnne_abort()
function. Seeoverride.c
in theExportingAssembly
project for an example.
- For all non-recoverable scenarios, DNNE will call the standard C
- How can I add documentation to the exported function in the header file?
- Add the normal triple-slash comments to the exported functions and then set the MSBuild property
GenerateDocumentationFile
totrue
in the project. The compiler will generated xml documentation for the exported C# functions and that will be be added to the generated header file.
- Add the normal triple-slash comments to the exported functions and then set the MSBuild property
- How can I keep my project cross-platform and generate a native binary for other platforms than the one I am currently building on?
- The managed assembly will remain cross-platform but the native component is difficult to produce due to native tool chain constraints. In order to accomplish this on the native side, there would need to exist a C99 tool chain that can target any platform from any other platform. For example, the native tool chain could run on Windows but would need to provide a macOS SDK, linux SDK, and produce a macOS
.dylib
(Mach-O image) and/or a linux.so
(ELF image). If such a native tool chain exists, it would be possible.
- The managed assembly will remain cross-platform but the native component is difficult to produce due to native tool chain constraints. In order to accomplish this on the native side, there would need to exist a C99 tool chain that can target any platform from any other platform. For example, the native tool chain could run on Windows but would need to provide a macOS SDK, linux SDK, and produce a macOS