compiler-warning-level-1-c4731.md

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Learn more about: Compiler Warning (Level 1) C4731	Compiler Warning (Level 1) C4731	11/04/2016	C4731	C4731	5658c24c-3e6f-4505-835b-1fb92d47cab0

Compiler Warning (Level 1) C4731

'pointer' : frame pointer register 'register' modified by inline assembly code

A frame pointer register was modified. You must save and restore the register in your inline assembly block or frame variable (local or parameter, depending on the register modified), or your code may not work properly.

The following sample generates C4731:

// C4731.cpp
// compile with: /W1 /LD
// processor: x86
// C4731 expected
void bad(int p) {
   __asm
   {
      mov ebp, 1
   }

   if (p == 1)
   {
      // ...
   }
}

EBP is the frame pointer (FPO is disallowed) and it is being modified. When p is later referenced, it is referenced relative to EBP. But EBP has been overwritten by the code, so the program will not work properly and may even fault.