From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/3424 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 17:26:19 +0200 Message-ID: <1371396379.5692.96.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> 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="=-zP7Tat/sw3/ZEZDedrFZ" X-Trace: ger.gmane.org 1371396393 12913 80.91.229.3 (16 Jun 2013 15:26:33 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 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:3424 Archived-At: --=-zP7Tat/sw3/ZEZDedrFZ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hello, Am Sonntag, den 16.06.2013, 10:31 -0400 schrieb Rich Felker: > Is there no way to make the suppression more fine-grained? For > example, "ignore up to wordsize-1 sequential invalid reads in this > function" would give the desired behavior. glibc has some sort of > suppression for these functions; what does valgrind do for glibc? I think it basically wraps its own code around some functions. Or maybe just replaces them? Such an approach obviously doesn't work if we link the C library statically. I just wanted to try to link statically against glibc to see what happens, but got stuck with other stuff. > > 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. 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. So this uses the fact that the newly allocated memory has an unspecified, but determined value to do some optimization. It is exactly that line of calloc.c, namely the `if` in line 20 that triggers under valgrind. In a recent discussion with the C committee I have learned that there is no consensus of whether an unspecified value is determined and wouldn't change once it is observed or whether it could be "wobbling" (the term that someone used, there). There are even people that propose to have a sort of state outside the object representation that captures if memory has been initialized or not. 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 :: --=-zP7Tat/sw3/ZEZDedrFZ 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) iEYEABECAAYFAlG92RwACgkQD9PoadrVN+JW+gCgi+3CGxh+J+SfkHR6SM+YZasf re8An1oJk7b3TH/3nm9z0Hr5BXyhBpof =UKwW -----END PGP SIGNATURE----- --=-zP7Tat/sw3/ZEZDedrFZ--