Thread: Tiny patch: sigmask.diff

Hello

sigmask macro is defined in win32.h like this:

```
#define sigmask(sig) ( 1 << ((sig)-1) )
```

And used in signal.c in this fashion:

```
        for (i = 0; i < PG_SIGNAL_COUNT; i++)
        {
            if (exec_mask & sigmask(i))
            {
```

Thus during first iteration we are doing `<< -1`. I think it's a bug.

Patch attached.

--
Best regards,
Aleksander Alekseev
http://eax.me/

Aleksander Alekseev <a.alekseev@postgrespro.ru> writes:
> sigmask macro is defined in win32.h like this:
> #define sigmask(sig) ( 1 << ((sig)-1) )

> And used in signal.c in this fashion:
>         for (i = 0; i < PG_SIGNAL_COUNT; i++)
>             if (exec_mask & sigmask(i))

> Thus during first iteration we are doing `<< -1`. I think it's a bug.

Agreed.

> Patch attached.

Surely this fix is completely wrong?  You'd have to touch every use of
signum() to do it like that.  You'd also be introducing similarly-
undefined behavior at the other end of the loop, where this coding
would be asking to compute 1<<31, hence shifting into the sign bit,
which is undefined unless you make the computation explicitly unsigned.

I think better is just to change the for-loop to iterate from 1 not 0.
Signal 0 is invalid anyway, and is rejected in pg_queue_signal for
example, so there can't be any event waiting there.
        regards, tom lane

> Surely this fix is completely wrong?  You'd have to touch every use of
> signum() to do it like that.  You'd also be introducing similarly-
> undefined behavior at the other end of the loop, where this coding
> would be asking to compute 1<<31, hence shifting into the sign bit,
> which is undefined unless you make the computation explicitly
> unsigned.

Oh, I didn't think about that...

> I think better is just to change the for-loop to iterate from 1 not 0.
> Signal 0 is invalid anyway, and is rejected in pg_queue_signal for
> example, so there can't be any event waiting there.

Agreed.

--
Best regards,
Aleksander Alekseev
http://eax.me/