Messages in this thread | | | Date | Wed, 26 Feb 2003 09:20:54 -0800 | Subject | Re: Invalid compilation without -fno-strict-aliasing | From | Jean Tourrilhes <> |
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On Tue, Feb 25, 2003 at 11:33:09PM -0500, Albert Cahalan wrote: > Jean Tourrilhes writes: > > > 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. > > > > Have fun... > > Since (char*) is special, I agree that it's a bug. > In any case, a warning sure would be nice! > > Now for the fun. Pass iwe->len into this > macro before the memcpy, and all should be well. > > #define FORCE_TO_MEM(x) asm volatile(""::"r"(&(x))) > > Like this: > > iwe->len = event_len; > FORCE_TO_MEM(iwe->len); > memcpy(stream, (char *) iwe, event_len);
I'll try that, that sounds absolutely clever (but I only understand half of it). Thanks a lot !
Jean - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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