How to disable a programmatical breakpoint / assert?

Question

I am using Visual Studio, developing a native application, I have a programmatical breakpoint (assert) in my code placed using __asm int 3 or __debugbreak. Sometimes when I hit it, I would like to disable it so that successive hits in the same debugging session no longer break into the debugger. How can I do this?

Heraclid

Answer 1

x86 / x64

Assuming you are writing x86/x64 application, write following in your watch window:

x86: *(char *)eip,x

x64: *(char *)rip,x

You should see a value 0xcc, which is opcode for INT 3. Replace it with 0x90, which is opcode for NOP. You can also use the memory window with eip as an address.

PPC

Assuming you are writing PPC application (e.g. Xbox 360), write following in your watch window:

*(int *)iar,x

You should see a value 0xfeNNNNNN, which is opcode for trap (most often 0x0fe00016 = unconditional trap). Replace it with 0x60000000, which is opcode for NOP.

Heraclid

on win32 you may have to make your code-segment writable. Great answer nevertheless! – Assembler

I am doing this on Win32 and I have never seen any code-segment writeability issues. Can you elaborate some more? I will be glad to incorporate any more details into the answer to make it better. – Heraclid

Answer 2

You might try something like this:

#define ASSERT(x) {\
   if (!(x)) \
   { \
      static bool ignore = false; \
      if (!ignore) \
      { \
         ignore = true; \
         __asm int 3 \
      } \
   }\
}

This should hit the debug only once. You might even show a messagebox to the user and ask what to do: continue (nothing happens), break (int 3 is called) or ignore (ignore is set to true, the breakpoint is never hit again)

Cardona