Re: Clang UndefinedBehaviorSanitize (Postgres14) Detected undefined-behavior

Em seg., 31 de ago. de 2020 às 14:00, Alvaro Herrera <alvherre@2ndquadrant.com> escreveu:

On 2020-Aug-31, Ranier Vilela wrote:

> More troubles with undefined-behavior.
>
> This type of code can leaves overflow:
> var = (cast) (expression);
> diff = (int32) (id1 - id2);
>
> See:
>     diff64 =  ((long int) d1 - (long int) d2);
>     diff64=-4294901760

Did you compile this with gcc -fwrapv?

gcc 10.2 -O2  -fwrapv

bool test1()

{

    unsigned int d1 = 3;

    unsigned int d2 = 4294901763;

    long int diff64 = 0;

    diff64 =  ((long int) d1 - (long int) d2);

    return (diff64 < 0);

}

 

output:

mov     eax, 1

        ret

What is a workaround for msvc 2019 (64 bits) and clang 64 bits (linux)?

transam.c:311:22: runtime error: unsigned integer overflow: 3 - 4294901763 cannot be represented in type 'unsigned int'