Re: [PATCH ] POSIX clocks & timers take 3 (NOT HIGH RES)

[george anzinger <george@mvista.com>]

Stephen Rothwell wrote:
> 
> Hi George,
> 
> On Thu, 17 Oct 2002 16:10:26 -0700 george anzinger <george@mvista.com> wrote:
> >
> > +++ linux/include/asm-generic/siginfo.h       Thu Oct 17 15:33:39 2002
> > @@ -43,8 +43,9 @@
> >
> >               /* POSIX.1b timers */
> >               struct {
> > -                     unsigned int _timer1;
> > -                     unsigned int _timer2;
> > +                     timer_t _tid;           /* timer id */
> > +                     int _overrun;           /* overrun count */
> > +                     sigval_t _sigval;       /* same as below */
> >               } _timer;
> 
> This, of course, will only work on architectures where (sizeof(timer_t) +
> sizeof(int) + alignment padding for sigval_t) is the same as
> (sizeof(pid_t) + sizeof(uid_t) + alignment padding for sigval_t). Which is
> true as far as I can see, but is fragile.  It might be worth a comment.

Hm..., yes, but I would rather express such things as
something that will cause the compiler to complain (i.e.
stop, not just warn).  Possibly something like:

static int
dummy[sizeof(timer_t)+sizeof(int)-sizeof(pid_t)-sizeof(uid_t)];
static int
dummy2[sizeof(pid_t)+sizeof(uid_t)-sizeof(timer_t)-sizeof(int)-];

It is UGLY, but it does cause the right thing (i.e. a
failure) to happen when things are wrong.

Or we could do the same sort of thing on the offset of
_sigval in the several unions, which is what we really care
about.

Thanks for the comments.

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-- 
George Anzinger   george@mvista.com
High-res-timers: 
http://sourceforge.net/projects/high-res-timers/
Preemption patch:
http://www.kernel.org/pub/linux/kernel/people/rml