Messages in this thread | | | Date | Wed, 26 Feb 2003 15:57:54 -0500 | From | Daniel Jacobowitz <> | Subject | Re: Invalid compilation without -fno-strict-aliasing |
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On Wed, Feb 26, 2003 at 05:47:48PM -0300, Horst von Brand wrote: > Falk Hueffner <falk.hueffner@student.uni-tuebingen.de> said: > > Horst von Brand <vonbrand@inf.utfsm.cl> writes: > > > Jean Tourrilhes <jt@bougret.hpl.hp.com> said: > > > > if((stream + event_len) < ends) { > > > > iwe->len = event_len; > > > > memcpy(stream, (char *) iwe, event_len); > > > > stream += event_len; > > > > } > > > > return stream; > > > > } > > > > > > The compiler is free to assume char *stream and struct iw_event *iwe > > > point to separate areas of memory, due to strict aliasing. > > > > The relevant paragraph of the C99 standard is: > > > > An object shall have its stored value accessed only by an lvalue > > expression that has one of the following types: > [...] > > -- a character type. > > (char *) gives you a (pointer to) a character type. > > > I can't really spot any lvalue here that might violate this rule. It > > would be nice if somebody could report a bug with a testcase. > > stream and (char *) iwe
Stream is not the same storage as iwe, so this is hardly the issue. Writes to stream don't affect iwe. The problem was the assignment to iwe->len being moved after the access, according to the report.
-- Daniel Jacobowitz MontaVista Software Debian GNU/Linux Developer - 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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