cvs commit: src/sys/sys param.h

[Bruce Evans]

On Thu, 6 Dec 2007, Kip Macy wrote:

> kmacy       2007-12-06 04:00:59 UTC
>
>  FreeBSD src repository
>
>  Modified files:
>    sys/sys              param.h
>  Log:
>  Respect the fact that the value a may be constant so cast to const uint8_t *
>
>  Revision  Changes    Path
>  1.318     +2 -2      src/sys/sys/param.h

The correct fix is to back out 1.317.  If not, at least spell `unsigned
char' correctly and fix the other new style bug (a line longer than
80 characters from adding `const').  Using uint8_t is only a style bug
since POSIX probably requires unsigned char to be the same as uint8_t.
If unsigned char is larger than uint8_t, then revs.1.317-318 give
undefined behaviour (aliasing bugs) and clearly broken behaviour (wrong
divisor NBBY).  These bugs are easy to avoid by using the correct
spelling.

The case where the pointer is to volatile unsigned char remains broken,
and shouldn't be fixed by always casting to volatile const unsigned char *.
It almost makes sense to use the original macros on volatiles (volatility
would guarantee certain accesses), but casting to a smaller type is
guaranteed to give different accesses, so always casting to volatile would
silently break some cases (cases which didn't work before).

Bruce