Date: Wed, 16 Oct 2019 13:15:52 +0200 From: Jan Behrens <jbe-mlist@magnetkern.de> To: freebsd-questions@freebsd.org Subject: Re: Problems with ld, libc, and "struct stat" Message-ID: <20191016131552.6fda34292987e22ae78072cc@magnetkern.de> In-Reply-To: <47c27361-4e74-05d1-3343-e39526730d85@malikania.fr> References: <20191015204400.e33c8f62af711e829288ddae@magnetkern.de> <47c27361-4e74-05d1-3343-e39526730d85@malikania.fr>
next in thread | previous in thread | raw e-mail | index | archive | help
On Wed, 16 Oct 2019 09:18:52 +0200 David Demelier <markand@malikania.fr> wrote: > Le 15/10/2019 à 20:44, Jan Behrens a écrit : > > I stumbled across a weird problem related stat() that (according to my > > research) seems to be related to an update of the "struct stat" > > C-structure in recent Kernel versions. > > > > [...] > > > > stat("testlib.c", &sb); > > Please test the result of stat otherwise sb is left untouched (so all > member undefined). You are right, of course (this was just a quick and dirty demonstration). > > But when I make a shared library like this, I get a different result: > > > > % ld -shared -o testlib.so testlib.o > > Hmm, we usually never call the linker itself when creating shared libraries. > > Try instead: cc -shared -o testlib.so testlib.o > > HTH > -- > David Thank you very much; I tried that, and it works properly: % cc -Wall -c -fPIC -o testlib.o testlib.c % cc -shared -o testlib.so testlib.o % cc -Wall -o testprog `pwd`/testlib.so testprog.c % ./testprog Size of testlib.c is 168 bytes. I will from now on use cc instead of ld to create shared libraries. I still wonder though if there is any documentation on this behavior (and where to find it), whether it's FreeBSD related or LLVM related. It feels a bit scary that using "ld" to make a shared library can result in weird runtime behavior without even raising a warning. Do you know any link where I find a more detailed explanation about why I need to use "cc" instead of "ld" to create shared libraries? I assume that "cc" adds the necessary options to "ld" that are otherwise missing. But I don't see where this is documented. When I search the man page for "cc" (clang - the Clang C, C++, and Objective-C compiler), I even do not find any "-shared" option at all. Only in the "ld" manpage (ld.lld – ELF linker from the LLVM project), there is an entry about the "-shared" option: --shared Build a shared object. Following the man pages, I would naïvely use "ld", which leads to the bad and unexpected results as described in my original post. Thanks again Jan P.S.: My setup is: % freebsd-version 12.0-RELEASE-p10 % uname -i -K -m -p -r -s -U -v FreeBSD 12.0-RELEASE-p10 FreeBSD 12.0-RELEASE-p10 GENERIC amd64 amd64 GENERIC 1200086 1200086 % cc --version FreeBSD clang version 6.0.1 (tags/RELEASE_601/final 335540) (based on LLVM 6.0.1) Target: x86_64-unknown-freebsd12.0 Thread model: posix InstalledDir: /usr/bin % ld --version LLD 6.0.1 (FreeBSD 335540-1200005) (compatible with GNU linkers)
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20191016131552.6fda34292987e22ae78072cc>