From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/3414 Path: news.gmane.org!not-for-mail From: Jens Gustedt Newsgroups: gmane.linux.lib.musl.general Subject: Re: [PATCH] bugfix: initialize a state variable in lio_wait Date: Sun, 16 Jun 2013 11:31:58 +0200 Message-ID: <1371375118.16425.368.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> 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="=-EmRRFoL+k0NbiPrSek/C" X-Trace: ger.gmane.org 1371375131 22926 80.91.229.3 (16 Jun 2013 09:32:11 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 16 Jun 2013 09:32:11 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: 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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:3414 Archived-At: --=-EmRRFoL+k0NbiPrSek/C Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Am Sonntag, den 16.06.2013, 09:22 +0200 schrieb Jens Gustedt: > But then I also checked with clang, and it doesn't find this > either. First, I thought that the control flow surrounding this must > be fundamentally flawed if the compilers aren't capable to track such > simple cases of uninitialized variables. But even by simplifying, it > doesn't trigger, so I am not sure what is going on. I checked the assembler that is produced, and the reason that the bug might not trigger for most people is that the variable ends up in ebx which is nulled anyway at the beginning of the function. Then, depending on how that (static) function might be inlined or not in the context of the calling function and in which hardware register the variable ends up, there, this could trigger the bug or not. In all, this re-enforces my opinion to *always* initialize variables, unless I know that its address is immediately passed to an initialization function. If the compiler is good in computing the flow control for a given case, it will optimize it out if it is superfluous. If the flow control is too complicated for the compiler, it is probably too complicated for me, too. BTW, I used valgrind to help me finding such stuff on initialization, but the tons of false positives that musl triggers because of the str functions and calloc are really a pain. 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 :: --=-EmRRFoL+k0NbiPrSek/C 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) iEYEABECAAYFAlG9hg4ACgkQD9PoadrVN+JcfACeNcVrTjbo4T5aYroXtQx2nwdU w7cAnitVnj7T3j0R8KiXQIohwy+aAx+m =O/Va -----END PGP SIGNATURE----- --=-EmRRFoL+k0NbiPrSek/C--