MSIL Assembler (Ilasm.exe)

Switch View

MSIL Assembler (Ilasm.exe)

Collapse All

Language Filter

This page is specific to

Microsoft Visual Studio 2008/.NET Framework 3.5

Other versions are also available for the following:

.NET Framework Tools

MSIL Assembler (Ilasm.exe)

The MSIL Assembler generates a portable executable (PE) file from Microsoft intermediate language (MSIL). (For more information on MSIL, see Compiling to MSIL). You can run the resulting executable, which contains MSIL and the required metadata, to determine whether the MSIL performs as expected.

ilasm [options] filename [[options]filename...]

Parameters

Argument	Description
filename	The name of the .il source file. This file consists of metadata declaration directives and symbolic MSIL instructions. Multiple source file arguments can be supplied to produce a single PE file with Ilasm.exe. Note: Ensure that the last line of code in the .il source file has either trailing white space or an end-of-line character.

Option	Description
/alignment=integer	Sets FileAlignment to the value specified by integer in the NT Optional header. If the .alignment IL directive is specified in the file, this option overrides it.
/base=integer	Sets ImageBase to the value specified by integer in the NT Optional header. If the .imagebase IL directive is specified in the file, this option overrides it.
/clock	Measures and reports the following compilation times in milliseconds for the specified .il source file: Total Run: The total time spent performing all the specific operations that follow. Startup: Loading and opening the file. Emitting MD: Emitting metadata. Ref to Def Resolution: Resolving references to definitions in the file. CEE File Generation: Generating the file image in memory. PE File Writing: Writing the image to a PE file.
/debug[=IMPL\|OPT]	Includes debug information (local variable and argument names, and line numbers). Creates a PDB file. /debug with no additional value disables JIT optimization and uses sequence points from the PDB file. IMPL disables JIT optimization and uses implicit sequence points. OPT enables JIT optimization and uses implicit sequence points. IMPL and OPT are new in the .NET Framework version 2.0.
/dll	Produces a .dll file as output.
/enc=file	Creates Edit-and-Continue deltas from the specified source file. This argument is for academic use only and is not supported for commercial use. New in the .NET Framework version 2.0.
/exe	Produces an executable file as output. This is the default.
/flags=integer	Sets ImageFlags to the value specified by integer in the common language runtime header. If the .corflags IL directive is specified in the file, this option overrides it. See CorHdr.h , COMIMAGE_FLAGS for a list of valid values for integer.
/fold	Folds identical method bodies into one. New in the .NET Framework version 2.0.
/include=includePath	Sets a path to search for files included with #include. New in the .NET Framework version 2.0.
/itanium	Specifies Intel Itanium as the target processor. If no image bitness is specified, the default is /pe64. New in the .NET Framework version 2.0.
/key:keyFile	Compiles filename with a strong signature using the private key contained in keyFile.
/key:@keySource	Compiles filename with a strong signature using the private key produced at keySource.
/listing	Produces a listing file on the standard output. If you omit this option, no listing file is produced. This parameter is not supported in .NET Framework version 2.0 or later.
/mdv=versionString	Sets the metadata version string. New in the .NET Framework version 2.0.
/msv=major.minor	Sets the metadata stream version, where major and minor are integers. New in the .NET Framework version 2.0.
/noautoinherit	Disables default inheritance from Object when no base class is specified. New in the .NET Framework version 2.0.
/nocorstub	Suppresses generation of the CORExeMain stub. New in the .NET Framework version 2.0.
/nologo	Suppresses the Microsoft startup banner display.
/output:file.ext	Specifies the output file name and extension. By default, the output file name is the same as the name of the first source file. The default extension is .exe. If you specify the /dll option, the default extension is .dll. Note: Specifying /output:myfile.dll does not set the /dll option. If you do not specify /dll, the result will be an executable file named myfile.dll.
/optimize	Optimizes long instructions to short. For example, br to br.s. New in the .NET Framework version 2.0.
/pe64	Creates a 64-bit image (PE32+). If no target processor is specified, the default is /itanium. New in the .NET Framework version 2.0.
/pdb	Creates a PDB file without enabling debug information tracking. New in the .NET Framework version 2.0.
/quiet	Specifies quiet mode; does not report assembly progress.
/resource:file.res	Includes the specified resource file in .res format in the resulting .exe or .dll file. Only one .res file can be specified with the /resource* option.
/stack=stackSize	Sets the SizeOfStackReserve value in the NT Optional header to stackSize. New in the .NET Framework version 2.0.
/stripreloc	Specifies that no base relocations are needed. New in the .NET Framework version 2.0.
/subsystem=integer	Sets subsystem to the value specified by integer in the NT Optional header. If the .subsystem IL directive is specified in the file, this command overrides it. See winnt.h, IMAGE_SUBSYSTEM for a list of valid values for integer.
/x64	Specifies a 64-bit AMD processor as the target processor. If no image bitness is specified, the default is /pe64. New in the .NET Framework version 2.0.
/?	Displays command syntax and options for the tool.

Note:
All options for Ilasm.exe are case-insensitive and recognized by the first three letters. For example, /lis is equivalent to /listing and /res:myresfile.res is equivalent to /resource:myresfile.res. Options that specify arguments accept either a colon (:) or an equal sign (=) as the separator between the option and the argument. For example, /output:file.ext is equivalent to /output=file.ext.

Note:

All options for Ilasm.exe are case-insensitive and recognized by the first three letters. For example, /lis is equivalent to /listing and /res:myresfile.res is equivalent to /resource:myresfile.res. Options that specify arguments accept either a colon (:) or an equal sign (=) as the separator between the option and the argument. For example, /output:file.ext is equivalent to /output=file.ext.

Remarks

The MSIL Assembler helps tool vendors design and implement MSIL generators. Using Ilasm.exe, tool and compiler developers can concentrate on MSIL and metadata generation without being concerned with emitting MSIL in the PE file format.

Similar to other compilers that target the runtime, such as C# and Visual Basic, Ilasm.exe does not produce intermediate object files and does not require a linking stage to form a PE file.

The MSIL Assembler can express all the existing metadata and MSIL features of the programming languages that target the runtime. This allows managed code written in any of these programming languages to be adequately expressed in MSIL Assembler and compiled with Ilasm.exe.

Note:
Compilation might fail if the last line of code in the .il source file does not have either trailing white space or an end-of-line character.

You can use Ilasm.exe in conjunction with its companion tool, Ildasm.exe. Ildasm.exe takes a PE file that contains MSIL code and creates a text file suitable as input to Ilasm.exe. This is useful, for example, when compiling code in a programming language that does not support all the runtime metadata attributes. After compiling the code and running the output through Ildasm.exe, the resulting MSIL text file can be hand-edited to add the missing attributes. You can then run this text file through the Ilasm.exe to produce a final executable file.

You can also use this technique to produce a single PE file from several PE files originally generated by different compilers.

Note:
Currently, you cannot use this technique with PE files that contain embedded native code (for example, PE files produced by Visual C++).

To make this combined use of Ildasm.exe and Ilasm.exe as accurate as possible, the assembler does not perform some simple optimizations — it does not deduce whether to use short or long forms of instructions. For example, the tool does not try to determine whether it could substitute a short encoding for a long one you might have written in your MSIL sources (or that might be emitted by another compiler). If you want the short encoding, you must explicitly write that form. However, the assembler does check for out-of-range conditions where this is possible.

Note:
Ildasm.exe only operates on files on disk. It does not operate on files installed in the global assembly cache.

For more information about the grammar of MSIL, see the asmparse.grammar file in the Windows Software Development Kit (SDK).

Examples

The following command assembles the MSIL file myTestFile.il and produces the executable myTestFile.exe.

ilasm myTestFile

The following command assembles the MSIL file myTestFile.il and produces the .dll file myTestFile.dll.

ilasm myTestFile /dll

The following command assembles the MSIL file myTestFile.il and produces the .dll file myNewTestFile.dll.

ilasm myTestFile /dll /output:myNewTestFile.dll

The following code example shows an extremely simple application that displays "Hello World!" to the console. You can compile this code and then use the Ildasm.exe tool to generate an MSIL file.

using System;
public class Hello
{
    public static void Main(String[] args)
    {
        Console.WriteLine("Hello World!");
    }
}

The following MSIL code example corresponds to the previous C# code example. You can compile this code into an assembly using the MSIL Assembler (Ilasm.exe) tool. Both MSIL and C# code examples display "Hello World!" to the console.

// Metadata version: v2.0.50215
.assembly extern mscorlib
{
  .publickeytoken = (B7 7A 5C 56 19 34 E0 89 )                         // .z\V.4..
  .ver 2:0:0:0
}
.assembly sample
{
  .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilationRelaxationsAttribute::.ctor(int32) = ( 01 00 08 00 00 00 00 00 ) 
  .hash algorithm 0x00008004
  .ver 0:0:0:0
}
.module sample.exe
// MVID: {A224F460-A049-4A03-9E71-80A36DBBBCD3}
.imagebase 0x00400000
.file alignment 0x00000200
.stackreserve 0x00100000
.subsystem 0x0003       // WINDOWS_CUI
.corflags 0x00000001    //  ILONLY
// Image base: 0x02F20000


// =============== CLASS MEMBERS DECLARATION ===================

.class public auto ansi beforefieldinit Hello
       extends [mscorlib]System.Object
{
  .method public hidebysig static void  Main(string[] args) cil managed
  {
    .entrypoint
    // Code size       13 (0xd)
    .maxstack  8
    IL_0000:  nop
    IL_0001:  ldstr      "Hello World!"
    IL_0006:  call       void [mscorlib]System.Console::WriteLine(string)
    IL_000b:  nop
    IL_000c:  ret
  } // end of method Hello::Main

  .method public hidebysig specialname rtspecialname 
          instance void  .ctor() cil managed
  {
    // Code size       7 (0x7)
    .maxstack  8
    IL_0000:  ldarg.0
    IL_0001:  call       instance void [mscorlib]System.Object::.ctor()
    IL_0006:  ret
  } // end of method Hello::.ctor

} // end of class Hello

Concepts

Compiling to MSIL

Reference

.NET Framework Tools

MSIL Disassembler (Ildasm.exe)

SDK Command Prompt