Messages in this thread | | | Subject | Re: Invalid compilation without -fno-strict-aliasing | From | Albert Cahalan <> | Date | 25 Feb 2003 23:33:09 -0500 |
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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);
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