On Fri, Oct 26, 2012 at 10:00:13AM +0100, David Laight wrote:
> > Subject: [PATCH] sctp: Clean up type-punning in sctp_cmd_t union
> ...
> > +#define SCTP_NULL_BYTE 0xAA
> > static inline sctp_arg_t SCTP_NULL(void)
> > {
> > - sctp_arg_t retval; retval.ptr = NULL; return retval;
> > + sctp_arg_t retval;
> > + memset(&retval, SCTP_NULL_BYTE, sizeof(sctp_arg_t));
> > + return retval;
> > }
>
> You really don't want to be taking the address of a local
> variable that would normally be held in a register.
> It stops the compiler doing a lot of optimisations.
> In this case the structure is also being returned by value,
> not nice except that all(?) modern ABI do pass small structures
> in registers.
>
Thank you dave, I hadn't considered the implications of missed optimizations
when storing to a register here.
> An assignment of some member of the union to NULL would
> seem most appropriate.
> OTOH the code that uses this must be someones 'bright idea (tm)'
> that probably wasn't such a good idea after all.
>
nobody uses it currently, Its just that some state machine side effects don't
require an argument, but you still have to pass one in, so I was trying to
enhance this to make it obvious in a backtrace should someone inadvertently use
it in the future. I'm going to revert it though, a big fat zero is probably
just as clear.
Neil
> David
>
>
>
>
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