On Tue, Apr 26, 2011 at 11:41 AM, RW <rwmailli...@googlemail.com> wrote: >> The above quote states that the memory not occupied by the remapped >> object is zero filled. Which is to say that memory allocated by mmap() >> is either filled with new data or filled with zeros. > > In context it says: > > "If len is not a multiple of the page-size, the mapped region may > extend past the specified range. Any such extension beyond the > end of the mapped object will be zero-filled." > > To me the most straightforward reading of that is that it's referring > to non-aligned address ranges. > > Your interpretation may well be the intended one, but where would that > leave the anonymous mappings used by malloc? Are we to think of them as > extensions beyond a non-existent mapped object, and thus infer that they > are zero-filled? It's a bit of a stretch from what's written.
While it's not a *proof*, you could always do a little bit of black box testing. 1, So how about a little C program scanner.c that allocates a huge heap via mmap(2)'s malloc(3) backend, and crawls that buffer, looking for the first non-zero byte? If we always get zero-filled pages, you shouldn't find any non-zero bytes there. 2. For good measure, another program filler.c could fill a huge heap with a particular easily recognizable pattern (say something like 0xdeadbeef), and exit; and then, scanner.c could not only check for non-zero byes, but also for that particular pattern. -cpghost. -- Cordula's Web. http://www.cordula.ws/ _______________________________________________ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "freebsd-questions-unsubscr...@freebsd.org"
