| Format | Assembly Format | Description |
|---|---|---|
| 6F <T> | callvirt method |
Call a method associated with an object. |
…, obj, arg1, … argN → …, returnVal (not always returned)
The callvirt instruction calls a late-bound method on an object. That is, the method is chosen based on the exact type of obj rather than the compile-time class visible in the method metadata token. callvirt can be used to call both virtual and instance methods. See Partition I for a detailed description of the CIL calling sequence. The callvirt instruction can be immediately preceded by a tail. prefix to specify that the current stack frame should be released before transferring control. If the call would transfer control to a method of higher trust than the original method the stack frame will not be released.
[A callee of "higher trust" is defined as one whose permission grant-set is a strict superset of the grant-set of the caller]
method is a metadata token (a methoddef, methodref or methodspec see Partition II) that provides the name, class and signature of the method to call. In more detail, callvirt can be thought of as follows. Associated with obj is the class of which it is an instance. The CLI resolves the method to be called according to the rules specified in §I.12.4.1.3 (Computed destinations).
callvirt pops the object and the arguments off the evaluation stack before calling the method. If the method has a return value, it is pushed on the stack upon method completion. On the callee side, the obj parameter is accessed as argument 0, arg1 as argument 1, and so on.
The arguments are placed on the stack in left-to-right order. That is, the first argument is computed and placed on the stack, then the second argument, etc. The this pointer (always required for callvirt) shall be pushed first. The signature carried in the metadata does not contain an entry in the parameter list for the this pointer, but the calling convention always indicates whether one is required and if its signature is explicit or inferred (see §I.8.6.1.5 and §II.15.3) [Note: For calls to methods on value types, the this pointer may be a managed pointer, not an instance reference (§I.8.6.1.5). end note]
The arguments are passed as though by implicit starg (§III.3.61) instructions, see Implicit argument coercion §III.1.6.
Note that a virtual method can also be called using the call instruction.
System.MethodAccessException can be thrown when there is an invalid attempt to access a nonpublic method.
System.MissingMethodException is thrown if a non-static method with the indicated name and signature could not be found in obj's class or any of its base classes. This is typically detected when CIL is converted to native code, rather than at runtime.
System.NullReferenceException is thrown if obj is null.
System.SecurityException is thrown if system security does not grant the caller access to the called method. The security check can occur when the CIL is converted to native code rather than at runtime.
Correct CIL ensures that the destination method exists and the values on the stack correspond to the types of the parameters of the method being called. In addition to the arguments types allowed by Verified CIL, Correct CIL also allows a native int to be passed as a byref (&); in which case following the store the value will be tracked by garbage collection.
In its typical use, callvirt is verifiable if:
-
the above restrictions are met;
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the verification type of obj is verifier-assignable-to (§III.1.8.1.2.3) with the this signature of the method's signature;
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the types of the arguments on the stack are verifier-assignable-to (§III.1.8.1.2.3) the parameter signatures of the method's signature; and
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the method is accessible from the call site.
If returnVal is present its type is tracked as the intermediate type of the called method's signature return type.
A callvirt annotated by tail. has additional considerations – see §III.1.8.