-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 According to Corinna Vinschen on 11/9/2009 4:59 AM: >>> I just found that the latest autoconf *still* has this broken test >>> for mmap, which basically calls >>> >>> data2 = malloc (size); >>> mmap(data2, ...); >>> >>> Why has this test never been fixed? Chuck? >> ...err, 'cause I didn't realize it was a problem. I see that cygport has >> hidden this for years: >> >> # AC_HAVE_MMAP fails despite a working mmap, so we force this to yes >> # (see http://www.cygwin.com/ml/cygwin/2004-09/msg00741.html >> # and following thread for details) >> export ac_cv_func_mmap_fixed_mapped=yes; >> >> NTTAWWT, but it never triggered my "gee I ought to fix that" reflex. I >> agree this should be fixed, but I'm leery of changing an autoconf test >> without knowing how that change will affect the other 9,236 platforms > > The problem in this testcase is the fact that it calls malloc, then > computes the next page-aligned free address after the mallocated area > and then tries to mmap to this address with MAP_FIXED set. Sure, this > *might* work, and it works on most systems, but there's no reason at all > to *expect* that it works since it only works by chance. The memory > addresses can be taken by anything and to require that an arbitrary > fixed address is available to mmap is just plain wrong. From the > Linux man page: > > MAP_FIXED > [...] > If the specified address cannot be used, mmap() will fail. Because > requiring a fixed address for a mapping is less portable, the use of > this option is discouraged. > > Since autoconf is supposed to help applications to be more portable, > it's not really feasible, IMHO, that autoconf requires a non-portable > feature to work. > > It's frustrating that mmap() and even mmap(MAP_FIXED) > works fine on Cygwin, just not in the non-portable way it's tested > in the autoconf test. Maybe we need two mmap tests in autconf, one > for mmap in general, the other for MAP_FIXED iisues. > >> I think this is an issue for the autoconf list as a whole. Would you -- >> or Eric -- care to raise it there? Especially as you seemed to have >> quite strong feelings about it back in 2004: >> http://www.cygwin.com/ml/cygwin/2004-09/msg00753.html > > I had hoped that you, as the autoconf maintainer, would put this > upstream...
It's an upstream issue now ;) The problem is that I need some more advice from the cygwin list on how best to fix the test to pass on cygwin by default. I'm hoping to release autoconf 2.65 this week, so a speedy fix to help this issue go away before the release would be extra nice. - -- Don't work too hard, make some time for fun as well! Eric Blake e...@byu.net -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (Cygwin) Comment: Public key at home.comcast.net/~ericblake/eblake.gpg Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkr4D/sACgkQ84KuGfSFAYCOjwCghVcvxtUrAPxqB7w+/6gaT+Y/ H0EAoIUsDfqQ42NzKa8olQtBdhkvVS1f =36fe -----END PGP SIGNATURE----- -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
