flagging unsigned subtraction assigned to bigger signed number?

[Richard (Rikki) Andrew Cattermole]

On 21/05/2025 4:44 PM, Walter Bright wrote:
> This is a common issue. Unfortunately, nobody has come up with a 
> solution to this in the last 45 years. Since every combination of signed 
> and unsigned has well-defined behavior, prohibiting one of those 
> behaviors is going to break a lot of code. Changing the conversion rules 
> will break a lot of existing behavior. There's no way around it.

``$ gcc --analyzer file.c``

```c++
#include <stdio.h>

void test(unsigned int len, int* ptr) {
     for(int i = 0; i < len; i++) {
         int j = i - 1;
         printf("%d\n", ptr[j]);
     }
}

int main() {
     int val = 0;
     test(1, &val);
     return 0;
}
```

Some highlights of output (its a giant dump of awesomeness):

```
<source>:6:15: warning: stack-based buffer under-read [CWE-127] 
[-Wanalyzer-out-of-bounds]
out-of-bounds read from byte -4 till byte -1 but 'val' starts at byte 0
```

Clang-analyzer doesn't appear to have a solution to this (yet), but 
gcc's does appear to catch the obvious scenario here.