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SubjectRe: Invalid compilation without -fno-strict-aliasing
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On Wed, Feb 26, 2003 at 04:38:10PM +0100, Horst von Brand wrote:
> Jean Tourrilhes <jt@bougret.hpl.hp.com> said:
> > It looks like a compiler bug to me...
> > Some users have complained that when the following code is
> > compiled without the -fno-strict-aliasing, the order of the write and
> > memcpy is inverted (which mean a bogus len is mem-copied into the
> > stream).
> > Code (from linux/include/net/iw_handler.h) :
> > --------------------------------------------
> > static inline char *
> > iwe_stream_add_event(char * stream, /* Stream of events */
> > char * ends, /* End of stream */
> > struct iw_event *iwe, /* Payload */
> > int event_len) /* Real size of payload */
> > {
> > /* Check if it's possible */
> > if((stream + event_len) < ends) {
> > iwe->len = event_len;
> > memcpy(stream, (char *) iwe, event_len);
> > stream += event_len;
> > }
> > return stream;
> > }
> > --------------------------------------------
> > IMHO, the compiler should have enough context to know that the
> > reordering is dangerous. Any suggestion to make this simple code more
> > bullet proof is welcomed.
>
> The compiler is free to assume char *stream and struct iw_event *iwe point
> to separate areas of memory, due to strict aliasing.

Which is true and which is not the problem I'm complaining about.
Have fun...

Jean
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