From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/12600 Path: news.gmane.org!.POSTED!not-for-mail From: Szabolcs Nagy Newsgroups: gmane.linux.lib.musl.general Subject: Re: Program with constructor function segfaults frequently with musl Date: Thu, 15 Mar 2018 12:01:44 +0100 Message-ID: <20180315110143.GU4418@port70.net> References: Reply-To: musl@lists.openwall.com NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: blaine.gmane.org 1521111599 4924 195.159.176.226 (15 Mar 2018 10:59:59 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 15 Mar 2018 10:59:59 +0000 (UTC) User-Agent: Mutt/1.9.1 (2017-09-22) Cc: musl@lists.openwall.com To: Bracken Dawson Original-X-From: musl-return-12614-gllmg-musl=m.gmane.org@lists.openwall.com Thu Mar 15 11:59:55 2018 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by blaine.gmane.org with smtp (Exim 4.84_2) (envelope-from ) id 1ewQbv-00019b-O1 for gllmg-musl@m.gmane.org; Thu, 15 Mar 2018 11:59:51 +0100 Original-Received: (qmail 25866 invoked by uid 550); 15 Mar 2018 11:01:56 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 25848 invoked from network); 15 Mar 2018 11:01:55 -0000 Mail-Followup-To: Bracken Dawson , musl@lists.openwall.com Content-Disposition: inline In-Reply-To: Xref: news.gmane.org gmane.linux.lib.musl.general:12600 Archived-At: * Bracken Dawson [2018-03-15 10:38:31 +0000]: > I have been having trouble getting a cgo program to run with musl, it has > been segfaulting frequently and with 'No stack' when run under gdb. > > I have managed to reproduce such a failure in pure c with a very small > example: > > ``` > #include > #include > #include > > __attribute__((constructor)) void enter_namespace(int argc, char *argv[]) { the arguments passed to ctors are not part of the elf abi http://www.sco.com/developers/gabi/latest/ch5.dynamic.html#init_fini (and it cannot really work for dynamically loaded libraries anyway: the application can arbitrarily clobber argv by that time) glibc passes these arguments as an extension (the semantics for dlopened libraries is unclear), which happens to work since the calling convention of functions with no arguments allows this on all supported targets. (note that there are security hardenning solutions that check the call site function signature against the callee and abort on mismatch and such extension would not work with that) is this cgo that tries to capture argv in a ctor or some other c library? (in either case you should first try to solve it portably without depending on the glibc extension)