Date: Wed, 23 Apr 2008 14:09:42 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Garrett Cooper <yanefbsd@gmail.com> Cc: hackers@freebsd.org Subject: Re: Fwd: strdup(NULL) supposed to create SIGSEGV? Message-ID: <20080423110942.GU18958@deviant.kiev.zoral.com.ua> In-Reply-To: <7d6fde3d0804230219q13d204f2wda4a5f271b9a0e66@mail.gmail.com> References: <7d6fde3d0804222240j6b42b77yd86d8accb5a959fa@mail.gmail.com> <20080423025048.6b51a580@bhuda.mired.org> <5F412E73-29FC-4876-A6F0-9BC269876192@bitpowder.com> <7d6fde3d0804230219x209bd707u30150581abc74802@mail.gmail.com> <7d6fde3d0804230219q13d204f2wda4a5f271b9a0e66@mail.gmail.com>
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--dicp5grlxus9uUnk Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Apr 23, 2008 at 02:19:53AM -0700, Garrett Cooper wrote: > On Wed, Apr 23, 2008 at 1:30 AM, Bernard van Gastel <bvgastel@bitpowder.c= om> > wrote: >=20 > > > > Op 23 apr 2008, om 08:50 heeft Mike Meyer het volgende geschreven: > > > > > On Tue, 22 Apr 2008 22:40:21 -0700 > > > "Garrett Cooper" <yanefbsd@gmail.com> wrote: > > > > > > Hi all, > > > > I made an oops in a program, which uncovered "feature" in strdup= (2) > > > > that I wasn't aware of before. So I was wondering, is strdup(pointe= r =3D > > > > NULL) > > > > supposed to segfault should this just return NULL and set errno? > > > > > > > > > > Yes, it's supposed to segfault. Check out what, say, strcpy does if > > > you ask it to copy a NULL pointer. And this is an improvement from the > > > bad old days, when they would happily walk through memory starting at > > > 0..... > > > > > > > I don't like it this way. I would like: > > > > strdup(NULL) =3D NULL > > strdup(string) =3D copy of string > > > > strcpy(NULL, NULL) =3D NULL > > strcpy(s1, NULL) =3D ERROR > > strcpy(NULL, s2) =3D NULL (with s2 unchanged) > > strcpy(s1, s2) =3D normal > > > > But I am not sure of the implications. Maybe in some situation it is > > bad... Anyone? > > > > > > > Besides, errno is used to signal errors from system calls. strdup > > > isn't a system call, it's a library function (says so at the top of > > > the man page). > > > > > > > But strdup uses malloc, which is a system call (from the strdup manual:= If > > insufficient memory is available, NULL is returned and errno is set to > > ENOMEM.) > > > > Regards, > > Bernard > > > > > I was more concerned about the fact that there wasn't any documentation t= hat > said something -- either implicitly or explicitly -- that strdup(NULL) > causes a segfault. >=20 > Of course I did some more research after you guys gave me some replies and > realized I'm not the first person to bumble across this fact, but I haven= 't > found FreeBSD or Linux documentation supporting that errata. It was harml= ess > in my tiny program, but I would hate to be someone adding that assumption= to > a larger project with multiple threads and a fair number of lines... >=20 > *shrugs*. >=20 > -Garrett >=20 > PS I'm as much against POLA changes as the next guy. I just don't like > shooting myself in the foot too terribly much :). =46rom the ISO/IEC 9899:1999 (E), 7.1.4, clause 1 Each of the following statements applies unless explicitly stated otherwise in the detailed descriptions that follow: If an argument to a function has an invalid value (such as a value outside the domain of the function, or a pointer outside the address space of the program, or a null pointer, or a pointer to non-modifiable storage when the corresponding parameter is not const-qualified) or a type (after promotion) not expected by a function with variable number of arguments, the behavior is undefined. --dicp5grlxus9uUnk Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.8 (FreeBSD) iEYEARECAAYFAkgPGPYACgkQC3+MBN1Mb4jiQgCg209XplMxDf7aeX+OluO/u3WA M6IAn3aRbycSlXZMNMuSh0LiC9TS2M1D =F942 -----END PGP SIGNATURE----- --dicp5grlxus9uUnk--
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