__ud2

Article
12/18/2017

The latest version of this topic can be found at __ud2.

Microsoft Specific**

Generates an undefined instruction.

Syntax

void __ud2();

Remarks

The processor raises an invalid opcode exception if you execute an undefined instruction.

The __ud2 function is equivalent to the UD2 machine instruction, and is available only in kernel mode. For more information, search for the document, "Intel Architecture Software Developer's Manual, Volume 2: Instruction Set Reference," at the Intel Corporation site.

Requirements

Intrinsic	Architecture
`__ud2`	x86, x64

Header file <intrin.h>

END Microsoft Specific

Example

The following example executes an undefined instruction, which raises an exception. The exception handler then changes the return code from zero to one.

// __ud2_intrinsic.cpp  
#include <stdio.h>  
#include <intrin.h>  
#include <excpt.h>  
// compile with /EHa  
  
int main() {  
  
// Initialize the return code to 0.  
 int ret = 0;  
  
// Attempt to execute an undefined instruction.  
  printf("Before __ud2(). Return code = %d.\n", ret);  
  __try {   
  __ud2();   
  }  
  
// Catch any exceptions and set the return code to 1.  
  __except(EXCEPTION_EXECUTE_HANDLER){  
  printf("  In the exception handler.\n");  
  ret = 1;  
  }  
  
// Report the value of the return code.   
  printf("After __ud2().  Return code = %d.\n", ret);  
  return ret;  
}

Before __ud2(). Return code = 0.  
  In the exception handler.  
After __ud2().  Return code = 1.

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