Date: Tue, 31 Oct 2017 21:49:45 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Andreas Tobler <andreast-list@fgznet.ch> Cc: Tijl Coosemans <tijl@FreeBSD.org>, freebsd-current@FreeBSD.org, gerald@FreeBSD.org Subject: Re: Segfault in _Unwind_* code called from pthread_exit Message-ID: <20171031194945.GF2566@kib.kiev.ua> In-Reply-To: <9619a1f8-bb42-abc9-a4ee-3b93192f365e@fgznet.ch> References: <20170825234442.GO1700@kib.kiev.ua> <20170826202813.1240a1ef@kalimero.tijl.coosemans.org> <20170826184034.GR1700@kib.kiev.ua> <20171029182351.502f53cf@kalimero.tijl.coosemans.org> <20171029191358.GU2566@kib.kiev.ua> <9a724da4-70f1-4330-9a77-619739008a14@fgznet.ch> <20171030153207.15a42a1e@kalimero.tijl.coosemans.org> <9468430e-fda4-10f4-b6a0-aa40d7d64f5b@fgznet.ch> <20171031092803.GA2566@kib.kiev.ua> <9619a1f8-bb42-abc9-a4ee-3b93192f365e@fgznet.ch>
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On Tue, Oct 31, 2017 at 08:37:29PM +0100, Andreas Tobler wrote: > On 31.10.17 10:28, Konstantin Belousov wrote: > > On Mon, Oct 30, 2017 at 10:54:05PM +0100, Andreas Tobler wrote: > >> On 30.10.17 15:32, Tijl Coosemans wrote: > >>> On Sun, 29 Oct 2017 20:40:46 +0100 Andreas Tobler <andreast-list@fgznet.ch> wrote: > >>>> Attached what I have for libgcc. It can be applied to gcc5-8, should > >>>> give no issues. The mentioned tc from this thread and mine, > >>>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82635 do pass. > >>>> > >>>> What do you think? > >>> > >>> Like I said before the return address can be anything. It could for > >>> instance point to some instruction in a random function and then the > >>> stack unwinder will think thread_start was called from that function. > >>> There's no check you can add to libgcc to distinguish that from a > >>> normal valid return address. > >>> > >> Maybe not, and most probably I do not understand what is happening. But > >> with my modification I survive the test case. > >> > >> If no objections from your or Konstantin's side come up I will commit it > >> to the gcc repo. It will not 'fix' the issue, but it will improve the > >> gcc behavior. > > > > I posted something similar when the discussion thread started. From the > > cursory look, your patch is better than mine. The only difference that > > makes me wonder is that I used #ifdef KERN_PROC_SIGTRAMP around the > > block because I believe gcc has more relaxed policy about supporting > > obsoleted OS versions. > > I am aware about KERN_PROC_SIGTRAMP and older OS releases, that's why I > asked for feedback. > Do we, FreeBSD'ers, want to have gcc unwind support on older than > FreeBSD 9.3 releases? I think the gcc folks do not care, but we are the > ones who might have an need for such a support? Well, I put the #ifdef because I suspected that gcc folks cared, if anybody. For instance I know that perl people do. Is there some specific configuration bits in gcc that are only relevant for older releases ? If yes, then we perhaps should not break them until removed. If not, then it does not matter, most likely. > @Gerald, do you have an opinion? > > I can 'ifdef' the new code and in the 'else' case we fall back to the > already existing path.
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