On Sat, Sep 19, 2015 at 10:29 AM, Sebastien Marie <sema...@openbsd.org> wrote: > On Sat, Sep 19, 2015 at 10:07:04AM -0700, Philip Guenther wrote: >> On Sat, Sep 19, 2015 at 9:50 AM, Sebastien Marie <sema...@openbsd.org> wrote: >> > While working on building llvm 3.7.0 on openbsd (-current amd64 and >> > i386), I encounter a problem when linking a shared library, while >> > -Wl,-z,defs was passed on command-line. >> > >> > I build a minimal reproductible testcase: >> > >> > $ touch test.c >> > $ c++ -Wl,-z,defs -shared -o libtest.so test.c >> > /usr/lib/crtbeginS.o: In function `atexit': >> > (.text+0x18f): undefined reference to `__cxa_atexit' >> > collect2: ld returned 1 exit status >> >> If you want to use -zdefs when building a shared library, you MUST >> include in the link the libraries that it depends on, including libc. > > First, I encountered this problem while building clang. The linking of > libclang.so.3.7 use -Wl,-z,defs. > > For building with it, it would require -lc for several symbols, and the > last symbols will be `environ'. If I add `crt0.o' for `environ', it will > require `__init' and `main'.
Congrats, you found a bug in how things are spread between crt0 and libc! The result is that you can't use -zdefs when building a shared library. The fix is to not have libc depend on crt0, not to disable that functionality in ld. > I am not sure that I can provide them for linking libclang.so ? You can provide libc, but you can't (MUST NOT) provide crt0. >> I believe the current behavior is correct and matches other systems. > > I tested under Linux (debian wheezy) the testcase written before, and I > don't have any error like under OpenBSD. > > $ uname -a > Linux srvlinux 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt11-1+deb8u3 > (2015-08-04) x86_64 GNU/Linux > $ touch test.c > $ c++ -Wl,-z,defs -shared -o libtest.so test.c > $ ls libtest.so > libtest.so > $ Right, because their libc doesn't depend on their crt0. The whole point of -zdefs is to require a link to have all dependencies provided; it's not currently possible to do that on OpenBSD. Philip Guenther
