--- wikisrc/kernel_debugging_with_qemu.mdwn 2015/02/18 16:03:37 1.6 +++ wikisrc/kernel_debugging_with_qemu.mdwn 2021/12/27 14:26:28 1.19 @@ -9,30 +9,32 @@ You need a computer running an OS capabl (the "host system"). This can be NetBSD itself, Linux, or some other Unix-like OS. These instructions have been tested with NetBSD/amd64 6.1.4 and -Debian 7 hosts. +Debian 7 hosts. There should be at least 20 gigabytes of available +disk space. If your host system is running NetBSD, install the following packages from pkgsrc: * emulators/qemu >= 2.0.0nb4 -* misc/py-anita +* misc/py-anita >= 1.44 If your host system uses a package system other than pkgsrc, use that to install cvs, make, gcc, qemu, the Python pexpect -library, and genisoimage or mkisofs. Also download and +library, and genisoimage or mkisofs. Also download and install the most recent anita package from . ## Building the target system -Check out the NetBSD-current sources from CVS and build a full -NetBSD-current/i386 release with debug symbols using the build.sh -script. The i386 port is the preferred test platform because the two -other ports supported by anita are affected by known bugs: amd64 by -[[PR 49276|http://gnats.NetBSD.org/49276]], and sparc by -[[qemu bug 1335444|https://bugs.launchpad.net/qemu/+bug/1335444]]. +Check out the NetBSD-current sources from CVS and build a full release +of NetBSD-current/i386 with debug symbols using the build.sh script. +The i386 port is preferred because these instructions have been +successfully tested with it. +The amd64 port won't work because of [[PR 50128|http://gnats.NetBSD.org/50128]], +and sparc has not been tested since [[qemu bug +1399943|https://bugs.launchpad.net/qemu/+bug/1399943]] was fixed. -If you do the build in a directory other than /usr/src, +If you do the build in a directory other than /usr/src, use the -fdebug-prefix-map option to ensure that the source file names embedded in the debug symbols point to /usr/src, which is where the sources will be installed on the target system. For example: @@ -40,7 +42,7 @@ installed on the target system. For exa [[!template id=programlisting text=""" $ CVSROOT=anoncvs@anoncvs.NetBSD.org:/cvsroot cvs checkout -A -P src $ cd src - $ ./build.sh -j 4 -V MKDEBUG=YES -V COPTS="-g -fdebug-prefix-map=$(pwd)=/usr/src" -O ../obj -m i386 -U release sourcesets + $ ./build.sh -j 4 -V MKDEBUG=yes -V COPTS="-g -fdebug-prefix-map=$(pwd)=/usr/src" -O ../obj -m i386 -U release sourcesets """]] For best performance, change the number after "-j" to the number of CPU cores @@ -52,7 +54,7 @@ Install the system in a virtual machine, [[!template id=programlisting text=""" $ cd .. - $ anita --workdir work --disk-size 4G --memory-size 256M \ + $ anita --workdir work --disk-size 8G --memory-size 256M \ --sets kern-GENERIC,modules,base,etc,comp,debug,games,man,misc,tests,text,syssrc,src,sharesrc,gnusrc \ install $(pwd)/obj/releasedir/i386/ """]] @@ -60,39 +62,39 @@ Install the system in a virtual machine, ## Booting the VMs Next, start two qemu virtual machines, one to run the kernel being -debugged (the "kgdb target") and another to run gdb (the "kgdb host"). +debugged (the "target VM") and another to run gdb (the "gdb VM"). -The two VMS could be run on separate physical machines, but in this +The two VMs could be run on separate physical machines, but in this example, they are run on the same physical machine and share the same hard disk image. This sharing is made possible by the "-snapshot" option to qemu, which ensures that the disk image is not written to by either VM. -First start the kgdb target, enabling qemu's built-in GDB target stub +First start the target VM, enabling qemu's built-in GDB target stub on TCP port 1234: [[!template id=programlisting text=""" - $ qemu-system-i386 -nographic -snapshot -hda work/wd0.img -gdb tcp::1234 + $ qemu-system-i386 -nographic -snapshot -hda work/wd0.img -m 128 -gdb tcp::1234 """]] If you don't want everyone on the Internet to be able to debug your target, make sure incoming connections on port 1234 are blocked in your firewall. -In a second terminal window, start the kgdb host: +In a second terminal window, start the gdb VM: [[!template id=programlisting text=""" - $ qemu-system-i386 -nographic -snapshot -hda work/wd0.img + $ qemu-system-i386 -nographic -snapshot -hda work/wd0.img -m 256 """]] -Log in to the kgdb host as root and set up the network: +Log in to the gdb VM as root and set up the network: [[!template id=programlisting text=""" login: root # dhcpcd """]] -Start gdb on the kgdb host and connect to the target: +Start gdb on the gdb VM and connect to the target: [[!template id=programlisting text=""" # gdb /netbsd @@ -100,7 +102,7 @@ Start gdb on the kgdb host and connect t """]] where my.host.name is the domain name or IP address of the -physical machine running the kgdb target qemu VM. +host system. Now you should be able to get a stack trace and start debugging with full debug symbols and access to the source code: @@ -111,10 +113,8 @@ with full debug symbols and access to th """]] If the stack trace prints very slowly (like 30 seconds per stack -frame), it's likely because you are using a version of qemu where -the user-mode networking code fails to disable the Nagle algorithm. -This is fixed in the qemu in pkgsrc, but you may run into it if your -qemu is not installed via pkgsrc. +frame), you are probably using an old version of qemu that fails +to disable the Nagle algorithm. ## Qemu tips