amd64/116159: Panic while debugging on CURRENT

Joshua Isom jrisom at
Thu Sep 6 11:30:02 PDT 2007

>Number:         116159
>Category:       amd64
>Synopsis:       Panic while debugging on CURRENT
>Confidential:   no
>Severity:       critical
>Priority:       low
>Responsible:    freebsd-amd64
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Sep 06 18:30:01 GMT 2007
>Originator:     Joshua Isom
>Release:        CURRENT kernel, STABLE userland
FreeBSD freebsd 7.0-CURRENT FreeBSD 7.0-CURRENT #0: Wed Sep  5 06:32:03 CDT 2007     root at freebsd:/usr/obj/usr/src/sys/GENERIC  amd64

When I use a 6-STABLE userland with a 7-CURRENT kernel(for support for my dvd drive), I can predictably cause a panic in the kernel while debugging a program, and all as a non root user.  Looking at the coredump seems to provide no information but once it paniced I was able to get this information.

kdb_enter() at kdb_enter+0x31
panic() at panic+0x173
postsig() at postsig+0x155
thread_export_context() at thread_export_context+0x1c7
thread_userret() at thread_userret+0x481
userret() at userret+0xfb
trap() at trap+0x22d
calltrap() at calltrap+0x8

trap 0xc, rip=0xdc0038, rsp=0x7fffffffe730, rbp=0x7fffffffee760

The way I cause this is to debug a program that segfaults, and type in "next" or a similar command into gdb.  When I tried upgrading to a full CURRENT system, debugging anything seemed to be broken(one command would become zombied and I couldn't figure out which).  I don't have any problems with debugging with a 6-STABLE system.
$ gdb foo
> run
program went boom
> next
kernel goes boom
Unknown, but everything works in 6-STABLE.


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