Rules and Limitations for Naked Functions

 

The latest version of this topic can be found at Rules and Limitations for Naked Functions.

Microsoft Specific
The following rules and limitations apply to naked functions:

• The return statement is not permitted.

• Structured Exception Handling and C++ Exception Handling constructs are not permitted because they must unwind across the stack frame.

• For the same reason, any form of setjmp is prohibited.

• Use of the _alloca function is prohibited.

• To ensure that no initialization code for local variables appears before the prolog sequence, initialized local variables are not permitted at function scope. In particular, the declaration of C++ objects is not permitted at function scope. There may, however, be initialized data in a nested scope.

• Frame pointer optimization (the /Oy compiler option) is not recommended, but it is automatically suppressed for a naked function.

• You cannot declare C++ class objects at the function lexical scope. You can, however, declare objects in a nested block.

• The naked keyword is ignored when compiling with /clr.

• For __fastcall naked functions, whenever there is a reference in C/C++ code to one of the register arguments, the prolog code should store the values of that register into the stack location for that variable. For example:

// nkdfastcl.cpp  
// compile with: /c  
// processor: x86  
__declspec(naked) int __fastcall  power(int i, int j) {  
   // calculates i^j, assumes that j >= 0  
  
   // prolog  
   __asm {  
      push ebp  
      mov ebp, esp  
      sub esp, __LOCAL_SIZE  
     // store ECX and EDX into stack locations allocated for i and j  
     mov i, ecx  
     mov j, edx  
   }  
  
   {  
      int k = 1;   // return value  
      while (j-- > 0)   
         k *= i;  
      __asm {   
         mov eax, k   
      };  
   }  
  
   // epilog  
   __asm {  
      mov esp, ebp  
      pop ebp  
      ret  
   }  
}  

END Microsoft Specific

See Also

Naked Function Calls