Re: on-line kernel debugging
On Wed, Apr 25, 2018 at 1:54 AM, Il Ka wrote: > > I am also interested in kernel debugging. > > but we do support running gdb inside a system against its running kernel > Thank you for this recipe, but is it true that live debug does not work for > some cases? > You can't set break point in wsconsole and tty and debug them nor you can > debug kernel that > is frozen, and it seems that remote debug > (like http://www.netbsd.org/docs/kernel/kgdb.html) > is not supported by obsd, right? > Correct. > Is it because of security reasons? > No one was using it, it got in the way of development that was in progress, and none of the developers was interested in fixing it. If someone wants it and can keep it from being in the way of other work, then some form of it could come back in, but if it would just decay into an impediment then that would be a waste of time. Philip Guenther
Re: on-line kernel debugging
Hello, I am also interested in kernel debugging. > but we do support running gdb inside a system against its running kernel Thank you for this recipe, but is it true that live debug does not work for some cases? You can't set break point in wsconsole and tty and debug them nor you can debug kernel that is frozen, and it seems that remote debug (like http://www.netbsd.org/docs/kernel/kgdb.html) is not supported by obsd, right? Is it because of security reasons? -- Sent from: http://openbsd-archive.7691.n7.nabble.com/openbsd-dev-tech-f151936.html
Re: on-line kernel debugging
On 02/02/18 04:31, David Gwynne wrote: On 28 Jan 2018, at 04:07, bijan wrote: Thank you (for the quick response) and sorry if I was not as clear as I should have been! what I meant and was hoping to find was a source code debugger support, like gdb[1], where one can debug a running kernel with full access to the source code in a gdb session environment from a remote machine. I'm new to OpenBSD and found kgdb(7)[2] manual from 6.1 describing the process very similar to what I do daily with FreeBSD but (as I mentioned earlier) the code seems to be removed since 6.2. So, is there any alternative for remote debugging a running OpenBSD kernel using gdb? anyhow, I appreciate it if one can point me to the right direction and I don't mind any hard work in the process :-) i dont think we support kgdb anymore, but we do support running gdb inside a system against its running kernel. to do this, you need to have the kern.allowkmem sysctl set, which is best done via /etc/sysctl.conf. Great ... Thanks :-) I should definitely try this one Anyhow, I recently studied the FreeBSD source code for it's implementation of kdb and briefly examined the implementation and changes of ddb(4) in OpenBSD source code. It seems to me that it's possible to add support for multiple debuggers like gdb (as a standalone back-end or as a ddb command) to OpenBSD kernel as well (since the remote protocol is quiet small and the infrastructures looks pretty much the same as FreeBSD to me). I'm not quiet sure if I'm capable of porting the code, but if no-one is interested (or is free to do the job), I will definitely give it a try. So, is there anything one should know why such feature is missing? Or any reason to prevent such effort in the first place? Thanks B.E after that you'll need a kernel with debug symbols in it. the easiest way to get that is just build a kernel. there'll be a bsd.gdb next to the bsd it produces. then you can do this: dlg@v215 GENERIC.MP$ pwd /usr/obj/sys/arch/sparc64/compile/GENERIC.MP dlg@v215 GENERIC.MP$ ls bsd bsd.gdb -rwxrwx--- 1 dlg wobj 10193351 Feb 2 10:58 bsd -rwxrwx--- 1 dlg wobj 3915 Feb 2 10:58 bsd.gdb dlg@v215 GENERIC.MP$ cat /etc/sysctl.conf kern.allowkmem=1 dlg@v215 GENERIC.MP$ sysctl kern.allowkmem kern.allowkmem=1 dlg@v215 GENERIC.MP$ sudo gdb bsd.gdb GNU gdb 6.3 Copyright 2004 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "sparc64-unknown-openbsd6.2"... (gdb) target kvm #0 mi_switch () at /usr/src/sys/kern/sched_bsd.c:410 410 cpu_switchto(p, nextproc); (gdb) print copyright $1 = "Copyright (c) 1982, 1986, 1989, 1991, 1993\n\tThe Regents of the University of California. All rights reserved.\nCopyright (c) 1995-2017 OpenBSD. All rights reserved. https://www.OpenBSD.org\n"; the important thing is the "target kvm" inside gdb, which relies on allowkmem. because of the allowkmem requirement, this recommended for use on development boxes only. dlg
Re: on-line kernel debugging
> On 28 Jan 2018, at 04:07, bijan wrote: > > Thank you (for the quick response) and sorry if I was not as clear > as I should have been! what I meant and was hoping to find was > a source code debugger support, like gdb[1], where one can debug > a running kernel with full access to the source code in a gdb session > environment from a remote machine. > > I'm new to OpenBSD and found kgdb(7)[2] manual from 6.1 describing > the process very similar to what I do daily with FreeBSD but (as I > mentioned earlier) the code seems to be removed since 6.2. > > So, is there any alternative for remote debugging a running OpenBSD > kernel using gdb? anyhow, I appreciate it if one can point me to the > right direction and I don't mind any hard work in the process :-) i dont think we support kgdb anymore, but we do support running gdb inside a system against its running kernel. to do this, you need to have the kern.allowkmem sysctl set, which is best done via /etc/sysctl.conf. after that you'll need a kernel with debug symbols in it. the easiest way to get that is just build a kernel. there'll be a bsd.gdb next to the bsd it produces. then you can do this: dlg@v215 GENERIC.MP$ pwd /usr/obj/sys/arch/sparc64/compile/GENERIC.MP dlg@v215 GENERIC.MP$ ls bsd bsd.gdb -rwxrwx--- 1 dlg wobj 10193351 Feb 2 10:58 bsd -rwxrwx--- 1 dlg wobj 3915 Feb 2 10:58 bsd.gdb dlg@v215 GENERIC.MP$ cat /etc/sysctl.conf kern.allowkmem=1 dlg@v215 GENERIC.MP$ sysctl kern.allowkmem kern.allowkmem=1 dlg@v215 GENERIC.MP$ sudo gdb bsd.gdb GNU gdb 6.3 Copyright 2004 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "sparc64-unknown-openbsd6.2"... (gdb) target kvm #0 mi_switch () at /usr/src/sys/kern/sched_bsd.c:410 410 cpu_switchto(p, nextproc); (gdb) print copyright $1 = "Copyright (c) 1982, 1986, 1989, 1991, 1993\n\tThe Regents of the University of California. All rights reserved.\nCopyright (c) 1995-2017 OpenBSD. All rights reserved. https://www.OpenBSD.org\n"; the important thing is the "target kvm" inside gdb, which relies on allowkmem. because of the allowkmem requirement, this recommended for use on development boxes only. dlg > > [1]: > https://www.freebsd.org/doc/en/books/developers-handbook/kerneldebug-online-gdb.html > [2]: https://man.openbsd.org/OpenBSD-6.1/kgdb.7 > > > On 01/27/18 21:00, Todd C. Miller wrote: >> On Sat, 27 Jan 2018 20:46:18 +0330, bijan wrote: >> >>> does OpenBSD support on-line kernel debugging as FreeBSD does[1]? >> Yes, see the ddb(4) manual page. >> >> - todd >
Re: on-line kernel debugging
Thank you (for the quick response) and sorry if I was not as clear as I should have been! what I meant and was hoping to find was a source code debugger support, like gdb[1], where one can debug a running kernel with full access to the source code in a gdb session environment from a remote machine. I'm new to OpenBSD and found kgdb(7)[2] manual from 6.1 describing the process very similar to what I do daily with FreeBSD but (as I mentioned earlier) the code seems to be removed since 6.2. So, is there any alternative for remote debugging a running OpenBSD kernel using gdb? anyhow, I appreciate it if one can point me to the right direction and I don't mind any hard work in the process :-) [1]: https://www.freebsd.org/doc/en/books/developers-handbook/kerneldebug-online-gdb.html [2]: https://man.openbsd.org/OpenBSD-6.1/kgdb.7 On 01/27/18 21:00, Todd C. Miller wrote: On Sat, 27 Jan 2018 20:46:18 +0330, bijan wrote: does OpenBSD support on-line kernel debugging as FreeBSD does[1]? Yes, see the ddb(4) manual page. - todd
Re: on-line kernel debugging
On Sat, 27 Jan 2018 20:46:18 +0330, bijan wrote: > does OpenBSD support on-line kernel debugging as FreeBSD does[1]? Yes, see the ddb(4) manual page. - todd
on-line kernel debugging
Hi! (Don't know if tech@ is the right place to ask such questions, just hope it is) does OpenBSD support on-line kernel debugging as FreeBSD does[1]? The only document I managed to find was a fairly old one[2] by QEMU over GNU/Linux but it seems kgdb(7) is removed since 6.2 (apparently for not even working before[3]). Thank you! [1]: https://www.freebsd.org/doc/en/books/developers-handbook/kerneldebug-online-ddb.html [2]: https://markshroyer.com/2013/01/debugging-openbsd-via-qemu/ [3]: https://github.com/openbsd/src/commits/master/sys/sys/kgdb.h
