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SubjectRe: Invalid compilation without -fno-strict-aliasing
Date
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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.
--
Dr. Horst H. von Brand User #22616 counter.li.org
Departamento de Informatica Fono: +56 32 654431
Universidad Tecnica Federico Santa Maria +56 32 654239
Casilla 110-V, Valparaiso, Chile Fax: +56 32 797513
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