From mboxrd@z Thu Jan 1 00:00:00 1970 Content-Type: multipart/mixed; boundary="===============1695285056965887307==" MIME-Version: 1.0 From: Mark Wielaard To: elfutils-devel@lists.fedorahosted.org Subject: Re: [PATCH] Add --core-pattern option to eu-stack Date: Fri, 28 Nov 2014 15:27:37 +0100 Message-ID: <1417184857.4954.53.camel@bordewijk.wildebeest.org> In-Reply-To: 20141127212711.GA29375@host2.jankratochvil.net --===============1695285056965887307== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable On Thu, 2014-11-27 at 22:27 +0100, Jan Kratochvil wrote: > On Thu, 27 Nov 2014 12:04:39 +0100, Mark Wielaard wrote: > > On Wed, 2014-11-26 at 15:32 +0100, Jan Kratochvil wrote: > > > Therefore they are dead at the core_pattern time, they cannot be ptra= ced and > > > therefore they cannot be unwound. One could only find them in the cor= e file > > > itself but that is outside of the scope of this eu-stack feature. > > = > > Why do you think that is out of scope? We get both the actual tid > > through the command line option and the core file through stdin. Can't > > we combine those two to get all information we want/need? > = > It could be extended that way but: > = > Currently elfutils is used only for the list of unwound PCs. There is mi= ssing > a big part of functionality present in GDB - displaying parameters, local > variables, entry-value recovered values, data types pretty printing etc. > And I have doubts unwind of non-crashed threads is useful at all. But that not what I suggested. Although I think it would be cool to extend eu-stack to also show arguments, locals, etc. That is an interesting project on its own separate from this work. > It is a new functionality on top of this patch that it has to read thread > registers from PT_NOTE but access the memory via ptraced crashed thread. > Fortunately core file PT_NOTE is first so it can be read quickly: > Program Headers: > Type Offset VirtAddr PhysAddr FileSiz = MemSiz Flg Align > NOTE 0x0004a0 0x0000000000000000 0x0000000000000000 0x0005f4 = 0x000000 0 > As reading the whole core file is in many times not possible (without some > better kernel core dumping interface): > -fsanitize=3Daddress locks up abrt-hook-ccpp > https://bugzilla.redhat.com/show_bug.cgi?id=3D1164548 Is this bug being hit by elfutils/libdwfl core file parsing or a specific issue with how abrt-hook-ccpp parses its input? I agree a nicer interface for /proc/sys/kernel/core_pattern would be appreciated. But that seems a kernel issue. We have to work with what we have now. systemd has a standard core_pattern hook systemd-coredump (that also uses elfutils/libdwfl to extract backtraces). Maybe we can work with them on a interface/daemon to provide access to client programs that wish to inspect the process/core? But again I think that is separate from what we are currently working on. > So I agree your proposal makes some sense but: > * I find it an incremental feature on top of this one. > * Given elfutils just lists the unwound PCs I do not see how it is usefu= l. > = > What is your - or Martin's - opinion on such feature given these contrain= ts? I think getting backtraces for one or more threads of a crashing/exiting process is an nice feature. My point is simply that I think that what you wrote is a nice feature that we need to make into something that is really usable. Whether that is by extending the support to something more generic like --wait-pid that can be used independent of the core_pattern filter or in providing in eu-stack all functionality expected from a core_pattern filter program so that it is just a drop in filter program doesn't really matter to me. All I am interested in is that the eu-stack feature will actually be used and is not just some example code that isn't really usable or used by actual users. Cheers, Mark --===============1695285056965887307==--