Annotation of wikisrc/kernel_debugging_with_qemu.mdwn, revision 1.11
1.1 wiki 1: # Introduction
2:
1.5 gson 3: This HOWTO explains how to set up a test environment for symbolic
4: debugging of the NetBSD kernel using a pair of QEMU virtual machines.
1.1 wiki 5:
1.5 gson 6: ## Prerequisites
1.3 wiki 7:
1.5 gson 8: You need a computer running an OS capable of cross-building NetBSD
9: (the "host system").
1.6 gson 10: This can be NetBSD itself, Linux, or some other Unix-like OS.
1.5 gson 11: These instructions have been tested with NetBSD/amd64 6.1.4 and
1.7 gson 12: Debian 7 hosts. There should be at least 20 gigabytes of available
13: disk space.
1.1 wiki 14:
1.5 gson 15: If your host system is running NetBSD, install the following packages
16: from pkgsrc:
1.1 wiki 17:
1.5 gson 18: * emulators/qemu >= 2.0.0nb4
19: * misc/py-anita
1.2 wiki 20:
1.5 gson 21: If your host system uses a package system other than pkgsrc,
22: use that to install cvs, make, gcc, qemu, the Python pexpect
23: library, and genisoimage or mkisofs. Also download and
24: install the most recent anita package from
25: <http://www.gson.org/netbsd/anita/download/>.
1.1 wiki 26:
1.5 gson 27: ## Building the target system
1.1 wiki 28:
1.11 ! gson 29: Check out the NetBSD-current sources from CVS and build a full release of
! 30: NetBSD-current/i386 or /amd64 with debug symbols using the build.sh
! 31: script. The i386 and amd64 ports are the preferred test platforms because
! 32: sparc, the only other port supported by anita, is affected by a known bug,
1.10 gson 33: [[qemu bug 1399943|https://bugs.launchpad.net/qemu/+bug/1399943]].
1.5 gson 34: If you do the build in a directory other than /usr/src,
35: use the -fdebug-prefix-map option to ensure that the source file names embedded
36: in the debug symbols point to /usr/src, which is where the sources will be
37: installed on the target system. For example:
1.2 wiki 38:
1.3 wiki 39: [[!template id=programlisting text="""
1.5 gson 40: $ CVSROOT=anoncvs@anoncvs.NetBSD.org:/cvsroot cvs checkout -A -P src
41: $ cd src
42: $ ./build.sh -j 4 -V MKDEBUG=YES -V COPTS="-g -fdebug-prefix-map=$(pwd)=/usr/src" -O ../obj -m i386 -U release sourcesets
1.3 wiki 43: """]]
44:
1.5 gson 45: For best performance, change the number after "-j" to the number of CPU cores
46: you have, or slightly more.
47:
48: ## Installing the target system
1.3 wiki 49:
1.5 gson 50: Install the system in a virtual machine, including the debug symbols and source code:
1.3 wiki 51:
52: [[!template id=programlisting text="""
1.5 gson 53: $ cd ..
54: $ anita --workdir work --disk-size 4G --memory-size 256M \
55: --sets kern-GENERIC,modules,base,etc,comp,debug,games,man,misc,tests,text,syssrc,src,sharesrc,gnusrc \
56: install $(pwd)/obj/releasedir/i386/
57: """]]
1.3 wiki 58:
1.5 gson 59: ## Booting the VMs
1.3 wiki 60:
1.5 gson 61: Next, start two qemu virtual machines, one to run the kernel being
1.9 gson 62: debugged (the "target VM") and another to run gdb (the "gdb VM").
1.3 wiki 63:
1.8 gson 64: The two VMs could be run on separate physical machines, but in this
1.5 gson 65: example, they are run on the same physical machine and share the same
66: hard disk image. This sharing is made possible by the "-snapshot"
67: option to qemu, which ensures that the disk image is not written to by
68: either VM.
1.3 wiki 69:
1.9 gson 70: First start the target VM, enabling qemu's built-in GDB target stub
1.5 gson 71: on TCP port 1234:
1.3 wiki 72:
73: [[!template id=programlisting text="""
1.5 gson 74: $ qemu-system-i386 -nographic -snapshot -hda work/wd0.img -gdb tcp::1234
1.3 wiki 75: """]]
76:
1.5 gson 77: If you don't want everyone on the Internet to be able to debug your
78: target, make sure incoming connections on port 1234 are blocked in
79: your firewall.
1.3 wiki 80:
1.9 gson 81: In a second terminal window, start the gdb VM:
1.3 wiki 82:
83: [[!template id=programlisting text="""
1.5 gson 84: $ qemu-system-i386 -nographic -snapshot -hda work/wd0.img
1.3 wiki 85: """]]
86:
1.9 gson 87: Log in to the gdb VM as root and set up the network:
1.3 wiki 88:
89: [[!template id=programlisting text="""
1.5 gson 90: login: root
91: # dhcpcd
1.3 wiki 92: """]]
93:
1.9 gson 94: Start gdb on the gdb VM and connect to the target:
1.3 wiki 95:
96: [[!template id=programlisting text="""
1.5 gson 97: # gdb /netbsd
98: (gdb) target remote my.host.name:1234
1.3 wiki 99: """]]
1.2 wiki 100:
1.5 gson 101: where my.host.name is the domain name or IP address of the
1.9 gson 102: host system.
1.5 gson 103:
104: Now you should be able to get a stack trace and start debugging
105: with full debug symbols and access to the source code:
1.2 wiki 106:
1.5 gson 107: [[!template id=programlisting text="""
108: (gdb) where
109: (gdb) list
110: """]]
1.2 wiki 111:
1.5 gson 112: If the stack trace prints very slowly (like 30 seconds per stack
113: frame), it's likely because you are using a version of qemu where
114: the user-mode networking code fails to disable the Nagle algorithm.
115: This is fixed in the qemu in pkgsrc, but you may run into it if your
116: qemu is not installed via pkgsrc.
1.2 wiki 117:
1.5 gson 118: ## Qemu tips
1.2 wiki 119:
1.5 gson 120: Here is a couple of useful qemu commands to know:
1.1 wiki 121:
1.5 gson 122: * Ctrl-a b will send a break which will make the NetBSD VM enter the ddb kernel debugger.
1.3 wiki 123:
1.5 gson 124: * Ctrl-a c will switch to the qemu monitor where you can enter commands like "quit" to exit qemu,
125: or do things like saving/restoring the VM to/from a file.
CVSweb for NetBSD wikisrc <wikimaster@NetBSD.org> software: FreeBSD-CVSweb