[OT] OT: Null checks.

[Timon Gehr]

On 5/6/25 03:43, Walter Bright wrote:
> 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.
> ...

Well, this is copied from druntime.

>> 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.

Well, I can. I should not have to do that though to get basic 
functionality that is a given in some other languages. I replied to the 
other post.