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

[Andreas Gustafsson <gson%gson.org@localhost>]

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

From: Andreas Gustafsson <gson%gson.org@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: kern/49603: Single-stepping into syscall reboots -current/amd64 under qemu
Date: Thu, 8 Oct 2015 12:11:20 +0300

 I have now re-run my automated test for this bug against a number
 additional NetBSD source dates, using qemu 2.4.0 from pkgsrc on a
 NetBSD 6.1.4 host. and I'm finding that the qemu guest will either
 reboot as reported in the original PR, or hang, depending on the
 source date being tested.
 
 My bisection script was only looking for a reboot, so my initial
 conclusion that stepping into a syscall was working before source date
 2014.12.14.18.14.15 was incorrect - the bisection runs for versions
 older than that date just happened to trigger a hang rather than a
 reboot.
 
 I also ran the test using qemu 1.1.2 on a Debian 7 host, and there it
 resulted in neither a reboot or lockup of the guest, but in qemu
 itself segfaulting.  That, at least, is definitely a qemu bug.
 
 Here is an updated recipe for reproducing the bug that doesn't require
 anita nor pkgsrc, and should work on any host that supports qemu (e.g.,
 Linux).  You will need a couple of gigabytes of free disk space for the
 uncompressed disk image.
 
    wget http://www.gson.org/bugs/qemu/NetBSD-amd64-2015.08.01.16.18.47-com0.img.gz
    gunzip NetBSD-amd64-2015.08.01.16.18.47-com0.img.gz
    qemu-system-x86_64 -nographic -snapshot NetBSD-amd64-2015.08.01.16.18.47-com0.img
    (wait for the qemu guest to boot to a login prompt)
    (log in as root; there is no password)
    gdb /bin/sync
    break sync
    run
    stepi
    stepi
    stepi
    (The qemu guest will either instantly reboot or hang, or qemu will segfault)
    (On real hardware, you just get another gdb prompt, and gdb is still responding)
 
 -- 
 Andreas Gustafsson, gson%gson.org@localhost