Re: kern/49603: Single-stepping into syscall reboots -current/amd64 under qemu

[David Laight <david%l8s.co.uk@localhost>]

The following reply was made to PR kern/49603; it has been noted by GNATS.

From: David Laight <david%l8s.co.uk@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: kern/49603: Single-stepping into syscall reboots -current/amd64 under qemu
Date: Mon, 26 Jan 2015 08:25:48 +0000

 On Sun, Jan 25, 2015 at 01:55:01PM +0000, Andreas Gustafsson wrote:
 > >Number:         49603
 > >Category:       kern
 > >Synopsis:       Single-stepping into syscall reboots -current/amd64 under qemu
 ...
 > When debugging a userland process using gdb under NetBSD-current/amd64
 > running in qemu virtual machine, single stepping into a system call
 > causes an instant reboot.  Root privileges are not required.
 > 
 > I ran an automated binary search to find when the problem first
 > appeard, and it pointed at src/sys/sys/ksyms.h 1.30, committed by
 > christos on CVS date 2014.12.14.18.14.15.
 
 That file looks unlikely.
 Sounds more like a qemu bug to do with faulting on the system
 call entry/exit instruction when 'single step' is enabled.
 
 > The reboot is consistently reproducible under qemu, but I have not
 > been able to reproduce it on physical hardware (tested on an AMD
 > Athlon64).  It also does not happen with the i386 port, only amd64.
 > 
 > >How-To-Repeat:
 > 
 > pkg_add py-anita
 > anita interact http://nyftp.netbsd.org/pub/NetBSD-daily/HEAD/201501250540Z/amd64/
 > (log in as root)
 > gdb /bin/sync
 > break sync
 > run
 > stepi
 > stepi
 > stepi
 
 Which instructions are being stepped over?
 Do you know if the syscall happens - ie is the
 error on the syscall entry, syscall exit or the
 following instruction.
 
 	David
 
 -- 
 David Laight: david%l8s.co.uk@localhost