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    SubjectRe: Invalid compilation without -fno-strict-aliasing
    Date
    From
    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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