mirror of
https://github.com/xen-project/xen.git
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Mukesh Rathor
2a5c8ad466
Signed-off-by: Mukesh Rathor <mukesh.rathor@oracle.com> Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
131 lines
4.1 KiB
Plaintext
131 lines
4.1 KiB
Plaintext
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gdbsx: gdbserver for xen
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Welcome to gdbsx. gdbsx is a gdbserver program to debug guest kernels and
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kernel modules. It runs on dom0 running on xen hypervisor and allows debug
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of 32 or 64bit PV or HVM elf guest binaries. It can also be run standalone,
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without remote gdb, to dump context of any/all VCPUs of any guest.
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It is divided in two parts, gx and xg. The former interacts with remote gdb,
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while latter interacts with xen and exports public APIs that can be used to
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create a plug in for any other debugger or binary type.
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USAGE:
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USAGE 1:
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- dom0> gdbsx -c 1 64 : displays VCPU contexts for 64bit guest with domid 1
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USAGE 2:
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- dom0> gdbsx -a 2 64 9999
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connects to a 64bit guest with domid 2 and waits for gdb connection
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- now, connect to the above gdbsx from a remote system or dom0 as:
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bash> gdb ./vmlinux (exact matching vmlinux of guest kernel)
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(gdb) target remote dom0:9999
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- Additionally, to debug 32bit loadable kernel modules, please do following:
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(gdb) p init_mm.pgd[3]
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$1 = {pgd = 0x1b874f027}
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(gdb) monitor pgd3 0x1b874f027 (Make sure value is in HEX)
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pgd3val set to: 0x1b874f027
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- use gdb as normal, breakpoints, single step, etc...
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- when need to break into gdb, instead of ctrl-c, just do "xm pause <domid>"
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on dom0 to pause the guest. this will break into gdb right away.
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- detach/quit from gdb (leave gdbsx alone) to gracefully exit.
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- if ctrl-c or core-dumped, make sure to do xm unpause if guest still paused.
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- multiple vcpus:
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o gdb>set scheduler-locking on : for single step of correct vcpu.
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o since gdb is not kernel debugger, vcpus are emulated via threads
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Thus, gdb>info threads : will show all vcpus. Then, switch thread
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to get to another vcpu, etc... Remember, gdb has it's own [thread]
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id, off by 1.
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- See below for some useful gdb macros. Please email me if you've more.
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NOTES:
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- For now, it is not possible to run gdbsx on a guest and gdb inside
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the same guest at the same time.
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- To report problems, please run gdbsx with -d and collect output.
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- VCPU offlining is not supported. Thus [0-NUMVCPUs] are all assumed active.
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TIPS:
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- make sure firewall is disabled on dom0 if running gdb on a different host.
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- Must be at least gdb version 6.5-16.x to debug el5 kernels.
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Mukesh Rathor
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Oracle Corporation,
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Redwood Shores, CA USA
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mukesh[dot]rathor[at]oracle[dot]com
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------------------------------------------------------------------------------
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USEFUL gdb macros:
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# Courtesy Zhigang W (http://10.182.120.78/tech/vt/ovm/debug/gdbinit.macros):
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define ps
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dont-repeat
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set $tasks = (struct list_head *)init_task->tasks
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set $offset = (unsigned long)&init_task->tasks - (unsigned long)&init_task
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set $task = $tasks
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set $task_entry = (struct task_struct *)((unsigned long)$task - $offset)
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printf "Pointer PID Command\n"
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printf "%p %-9d%s\n", $task_entry, $task_entry->pid, $task_entry->comm
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set $task = $task->next
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while $task != $tasks
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set $task_entry = (struct task_struct *)((unsigned long)$task - $offset)
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if ($task_entry->pid) != 0
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printf "%p %-9d%s\n", $task_entry, $task_entry->pid, $task_entry->comm
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end
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set $task = $task->next
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end
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end
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document ps
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Report a snapshot of the current processes.
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end
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define lsmod
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dont-repeat
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# 4 for 32bit kernels. 8 for 64bit kernels.
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set $sz = sizeof(long)
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set $mod = (struct list_head *)modules
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printf "modptr address name\n"
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while 1
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set $mod_entry = (struct module *)((unsigned long)$mod - $sz)
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if ($sz == 4)
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printf "%08lx %08lx %s\n", $mod_entry, \
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$mod_entry->module_core, $mod_entry->name
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else
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printf "%016lx %016lx %s\n", $mod_entry, \
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$mod_entry->module_core, $mod_entry->name
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end
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set $mod = $mod->next
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if ($mod == &modules)
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loop_break
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end
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end
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end
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document lsmod
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Show the list of modules loaded in the Linux kernel.
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end
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define log
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dont-repeat
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printf "%s", log_buf
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end
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document log
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Dump system message buffer.
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end
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------------------------------------------------------------------------------
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