From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/3429 Path: news.gmane.org!not-for-mail From: Jens Gustedt Newsgroups: gmane.linux.lib.musl.general Subject: Re: valgrind problems Date: Sun, 16 Jun 2013 17:58:52 +0200 Message-ID: <1371398332.5692.108.camel@eris.loria.fr> References: <1371333657.16425.350.camel@eris.loria.fr> <20130615221627.GB6548@port70.net> <20130616054006.GJ29800@brightrain.aerifal.cx> <1371367371.16425.363.camel@eris.loria.fr> <1371375118.16425.368.camel@eris.loria.fr> <1371379388.16425.372.camel@eris.loria.fr> <20130616143140.GL29800@brightrain.aerifal.cx> <1371396379.5692.96.camel@eris.loria.fr> <20130616153117.GO29800@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-VO4VPQKkG8IeOZU8/qWZ" X-Trace: ger.gmane.org 1371398344 30312 80.91.229.3 (16 Jun 2013 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Cj15cu23XZI4/826Px/xqB37z547sPH374oOvnKTsOb+1zuCoImZARM8ZiLlKkXcWOcoFRJ+Do/CwFO4e2DEe+9Ti+ZXA8ny/cU+X4bMKRZxZIVEiqXI6/+NKuUzPHb7z40ovnX3zx+Ctuq38HyuqWG7Tu+A0AAAAASUVORK5CYII= X-Mailer: Evolution 3.2.3-0ubuntu6 Xref: news.gmane.org gmane.linux.lib.musl.general:3429 Archived-At: --=-VO4VPQKkG8IeOZU8/qWZ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Am Sonntag, den 16.06.2013, 11:31 -0400 schrieb Rich Felker: > > > > Also for calloc I am not sure that when we switch off the false > > > > positive (where musl assumes a certain gcc behavior for what in > > > > general is UB) > > >=20 > > > musl is not assuming any gcc behavior. > >=20 > > unfortunately it does. as an optimization shortcut it reads the newly > > allocated bytes and if they are already 0, it doesn't write to > > them. >=20 > This is not gcc behavior. yes, I think it is gcc+platform behavior. the C standard makes no guarantee that this if (*z) *z=3D0; guarantees that *z is observably 0 afterwards. And the problem is not that *z could be UB (if size_t had traps) but that there is no guarantee that an undetermined value is stable between two reads (the first with that "if" and the second from the application that receives this). > It's behavior of it's own implementation of > malloc. From the implementation's standpoint, the object returned by > malloc does not have indeterminate value; otherwise it would be > impossible to link it with its bookkeeping information, contained in > the header of the object, and to later free it. In other words, if you > required the implementation to treat malloc as a black box, it would > be impossible to implement free. I agree with all of this, if you can guarantee that the memory *is* effectively zero'ed after calloc. With the current implementation in musl you can only do that with additional knowledge about the platform. Jens --=20 :: INRIA Nancy Grand Est :: http://www.loria.fr/~gustedt/ :: :: AlGorille ::::::::::::::: office Nancy : +33 383593090 :: :: ICube :::::::::::::: office Strasbourg : +33 368854536 :: :: ::::::::::::::::::::::::::: gsm France : +33 651400183 :: :: :::::::::::::::::::: gsm international : +49 15737185122 :: --=-VO4VPQKkG8IeOZU8/qWZ Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iEYEABECAAYFAlG94LwACgkQD9PoadrVN+JzmACePOakVVNnf4/7SDwuJYzSk6Fk 5KsAnjXWH237w/lYBVSf4wE4K87YWvi0 =yJye -----END PGP SIGNATURE----- --=-VO4VPQKkG8IeOZU8/qWZ--