Re: [9fans] how to avoid a memset() optimization

["Douglas A. Gwyn" <DAGwyn@null.net>]

Russ Cox wrote:
> My problem with volatile is that it means ``something
> weird is going on here'' but doesn't tell you what.

No, it mens "compiler, the access must really be
performed".  It is the programmer who decides whether
that is a requirement, and it could be for numerous
reasons, such as to assist in debugging, because the
"location" is a portal to an external device register,
because the object is shared among threads, etc.  In
this particular case it would be because the programmer
really wants the memory overwrite to occur regardless
of whether it is used any further.

>> You're right here, but for me defining secmemset
 >> is much bigger evil than just adding volatile to
 >> the buffer.
> Why?

For one thing, it doesn't work (unless you force
volatile qualification within secmemset), because
the invocation of secmemset can be optimized away
also.  (It is less likely than for memset, but it
is a possibility when the compiler can see the
caller and callee.)  Also you're in effect just
replacing the standard library function with your
own implementation, which will in general be slower
(a trade-off you might be willing to make) and one
more interface to specify (assuming a professional
software environment as opposed to just hacking).
In general one should have better things to do than
duplicating standard library functions.