Re: Tiny patch: sigmask.diff

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Aleksander Alekseev <a(dot)alekseev(at)postgrespro(dot)ru>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Tiny patch: sigmask.diff
Date: 2016-04-04 14:48:56
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Aleksander Alekseev <a(dot)alekseev(at)postgrespro(dot)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.


> 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

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