[OT] OT: Null checks.

[Walter Bright]

On 5/4/2025 1:28 PM, Timon Gehr wrote:
> ```
> private void _enforceNoOverlap(const char[] action,
>      uintptr_t ptr1, uintptr_t ptr2, const size_t bytes)
> {
>      const d = ptr1 > ptr2 ? ptr1 - ptr2 : ptr2 - ptr1;
>      if (d >= bytes)
>          return;
>      const overlappedBytes = bytes - d;
> 
>      UnsignedStringBuf tmpBuff = void;
>      string msg = "Overlapping arrays in ";
>      msg ~= action;
>      msg ~= ": ";
>      msg ~= overlappedBytes.unsignedToTempString(tmpBuff);
>      msg ~= " byte(s) overlap of ";
>      msg ~= bytes.unsignedToTempString(tmpBuff);
>      assert(0, msg);
> }
> ```

I would not write logging code like that that relied on the gc being in a 
working state.

> Unfortunately I had accidentally detached my debugger instead of getting the 
> backtrace at the time. It is possible that this is what is happening on the 
> user's machine, but I don't know. And I also have no idea where this overlap 
> might occur.
> 
> This just gives an invalid instruction even in dubs "release-debug" builds by 
> default unless using a custom druntime build. I just don't think this should 
> ever happen to anyone, even if there is some workaround, by default people will 
> run into this at least once and perhaps they will not be as lucky as me and see 
> it with a debugger attached.
> 

The -release switch causes `assert(0, "message")` to be replaced with "ud2" 
which generates a breakpoint for the debugger. It triggers an invalid opcode 
exception.

You could write a signal handler to intercept that. See my other post for how to 
write one.