Compiler Warning (Level 1) C4733

 

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The latest version of this topic can be found at Compiler Warning (Level 1) C4733.

Inline asm assigning to 'FS:0' : handler not registered as safe handler

A function modifying the value at FS:0 to add a new exception handler may not work with Safe Exceptions, because the handler may not be registered as a valid exception handler (see /SAFESEH).

To resolve this warning, either remove the FS:0 definition or turn off this warning and use .SAFESEH to specify the safe exception handlers.

The following sample generates C4733:

// C4733.cpp  
// compile with: /W1 /c  
// processor: x86  
#include "stdlib.h"  
#include "stdio.h"  
void my_handler()  
{  
   printf("Hello from my_handler\n");  
   exit(1);  
}  
  
int main()  
{  
   _asm {  
      push    my_handler  
      mov     eax, DWORD PTR fs:0  
      push    eax  
      mov     DWORD PTR fs:0, esp   // C4733  
   }  
  
   *(int*)0 = 0;  
}  

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