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Compiler Warning (Level 1) C4733
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Compiler Warning (Level 1) C4733

Error Message

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
// 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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