Messages in this thread | | | Date | Wed, 26 Feb 2003 09:22:15 -0800 | Subject | Re: Invalid compilation without -fno-strict-aliasing | From | Jean Tourrilhes <> |
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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...
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