Date: Tue, 16 Apr 1996 19:20:07 +1000
From: Bruce Evans <bde@zeta.org.au>
To: fenner@parc.xerox.com, freebsd-bugs@freefall.freebsd.org
Subject: Re: kern/1144: sig{add, del}set and sigismember fns don't check signo
Message-ID: <199604160920.TAA23895@godzilla.zeta.org.au>
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> >Obviously the macros would be much harder to fix
>
> Would they? How about
>
> #define sigaddset(set, signo) (((signo) <= 0 || (signo) >= NSIG) ?
> (errno = EINVAL, -1) :
> (*(set) |= 1 << ((signo) - 1), 0))
>
> (untested, as usual)
Try it with:
for (signo = 0; signo < 32; )
sigaddset(set, signo++);
or weird and not so weird things like:
void *s = set;
sigaddset(set, 1.234);
sigaddset(s, SIGINT);
which also fail for the standard macro, but would work for a prototyped
function.
It is possible to write it as a safe macro using Gnu C:
#define sigaddset(set, signo) \
({ struct sigaction *__set = set; \
int __signo = (signo); \
int __rv; \
\
/* 32 because NSIG is in application namespace. */ \
if (__signo <= 0 || __signo >= 32) { \
errno = EINVAL; \
__rv = -1; \
} else { \
*__set |= 1 << __signo; \
__rv = 0; \
} \
__rv; })
Untested, as usual.
Who wants all that for a function? It is probably a pessimization to
inline it unless signo is a constant. A larger and uglier gcc macro
could be used to handle the constant case inline and call a function
otherwise. Linux once used inline versions, but switched to function
versions because the macros aren't worth the trouble.
POSIX.1 1990 is unclearly written in this area. I think it allows our
current macros for everything except sigismember(). It doesn't
explictly require detection of errors, but it requires sigismember() to
either fail and return -1 or succeed and return a value other than 0 if
the signal isn't a member of the set. This fits well with most uses of
the macros - you check the signal number using sigismember(), or know
that it is valid, and then checking it in the other macros is a waste of
time.
Bruce
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