Date: Wed, 23 Apr 2008 02:19:53 -0700 From: "Garrett Cooper" <yanefbsd@gmail.com> To: hackers@freebsd.org Subject: Fwd: strdup(NULL) supposed to create SIGSEGV? Message-ID: <7d6fde3d0804230219q13d204f2wda4a5f271b9a0e66@mail.gmail.com> In-Reply-To: <7d6fde3d0804230219x209bd707u30150581abc74802@mail.gmail.com> References: <7d6fde3d0804222240j6b42b77yd86d8accb5a959fa@mail.gmail.com> <20080423025048.6b51a580@bhuda.mired.org> <5F412E73-29FC-4876-A6F0-9BC269876192@bitpowder.com> <7d6fde3d0804230219x209bd707u30150581abc74802@mail.gmail.com>
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On Wed, Apr 23, 2008 at 1:30 AM, Bernard van Gastel <bvgastel@bitpowder.com> wrote: > > 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(pointer = > > > 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) = NULL > strdup(string) = copy of string > > strcpy(NULL, NULL) = NULL > strcpy(s1, NULL) = ERROR > strcpy(NULL, s2) = NULL (with s2 unchanged) > strcpy(s1, s2) = 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 that said something -- either implicitly or explicitly -- that strdup(NULL) causes a segfault. 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 harmless 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... *shrugs*. -Garrett 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 :).
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