| 1 | <?xml version='1.0' encoding='UTF-8'?>
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| 2 | <!DOCTYPE topic PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
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| 3 | <topic xml:lang="en-us" id="ts_debugger">
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| 4 | <title>The Built-In VM Debugger</title>
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| 5 |
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| 6 | <body>
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| 7 | <p>
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| 8 | Oracle VM VirtualBox includes a built-in VM debugger, which advanced
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| 9 | users may find useful. This debugger enables you to examine and,
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| 10 | to some extent, control the VM state.
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| 11 | </p>
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| 12 | <note type="attention">
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| 13 | <p>
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| 14 | Use the VM debugger at your own risk. There is no support for
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| 15 | it, and the following documentation is only made available for
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| 16 | advanced users with a very high level of familiarity with the
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| 17 | x86/AMD64 machine instruction set, as well as detailed
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| 18 | knowledge of the PC architecture. A degree of familiarity with
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| 19 | the internals of the guest OS in question may also be very
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| 20 | helpful.
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| 21 | </p>
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| 22 | </note>
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| 23 | <p>
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| 24 | The VM debugger is available in all regular production versions
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| 25 | of Oracle VM VirtualBox, but it is disabled by default because the
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| 26 | average user will have little use for it. There are two ways to
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| 27 | access the debugger:
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| 28 | </p>
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| 29 | <ul>
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| 30 | <li>
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| 31 | <p>
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| 32 | Using a debugger console window displayed alongside the VM
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| 33 | </p>
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| 34 | </li>
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| 35 | <li>
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| 36 | <p>
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| 37 | Using the <userinput>telnet</userinput> protocol on port 5000
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| 38 | </p>
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| 39 | </li>
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| 40 | </ul>
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| 41 | <p>
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| 42 | The debugger can be enabled in the following ways:
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| 43 | </p>
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| 44 | <ul>
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| 45 | <li>
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| 46 | <p>
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| 47 | Start the VM directly using <userinput>VirtualBoxVM
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| 48 | --startvm</userinput>, with an additional
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| 49 | <codeph>--dbg</codeph>, <codeph>--debug</codeph>, or
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| 50 | <codeph>--debug-command-line</codeph> argument. See the
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| 51 | <userinput>VirtualBoxVM --help</userinput> command usage help
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| 52 | for details.
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| 53 | </p>
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| 54 | </li>
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| 55 | <li>
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| 56 | <p>
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| 57 | Set the <codeph>VBOX_GUI_DBG_ENABLED</codeph> or
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| 58 | <codeph>VBOX_GUI_DBG_AUTO_SHOW</codeph> environment
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| 59 | variable to <codeph>true</codeph> before launching the
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| 60 | Oracle VM VirtualBox process. Setting these variables, only their
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| 61 | presence is checked, is effective even when the first
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| 62 | Oracle VM VirtualBox process is the VM selector window. VMs
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| 63 | subsequently launched from the selector will have the
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| 64 | debugger enabled.
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| 65 | </p>
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| 66 | </li>
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| 67 | <li>
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| 68 | <p>
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| 69 | Set the <codeph>GUI/Dbg/Enabled</codeph> extra data item
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| 70 | to <codeph>true</codeph> before launching the VM. This can
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| 71 | be set globally or on a per VM basis.
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| 72 | </p>
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| 73 | </li>
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| 74 | </ul>
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| 75 | <p>
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| 76 | A new <b outputclass="bold">Debug</b> menu entry is added
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| 77 | to the Oracle VM VirtualBox application. This menu enables the user to
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| 78 | open the debugger console.
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| 79 | </p>
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| 80 | <p>
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| 81 | The VM debugger command syntax is loosely modeled on Microsoft
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| 82 | and IBM debuggers used on DOS, OS/2, and Windows. Users familiar
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| 83 | with symdeb, CodeView, or the OS/2 kernel debugger will find the
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| 84 | Oracle VM VirtualBox VM debugger familiar.
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| 85 | </p>
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| 86 | <p>
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| 87 | The most important command is <userinput>help</userinput>. This will
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| 88 | print brief usage help for all debugger commands. The set of
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| 89 | commands supported by the VM debugger changes frequently and the
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| 90 | <userinput>help</userinput> command is always up-to-date.
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| 91 | </p>
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| 92 | <p>
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| 93 | A brief summary of frequently used commands is as follows:
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| 94 | </p>
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| 95 | <ul>
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| 96 | <li>
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| 97 | <p><userinput>stop</userinput>: Stops the VM execution and enables
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| 98 | single stepping
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| 99 | </p>
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| 100 | </li>
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| 101 | <li>
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| 102 | <p><userinput>g</userinput>: Continue VM execution
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| 103 | </p>
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| 104 | </li>
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| 105 | <li>
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| 106 | <p><userinput>t</userinput>: Single step an instruction
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| 107 | </p>
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| 108 | </li>
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| 109 | <li>
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| 110 | <p><userinput>rg</userinput>, <userinput>rh</userinput>, and
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| 111 | <userinput>r</userinput>: Print the guest, hypervisor, and
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| 112 | current registers
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| 113 | </p>
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| 114 | </li>
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| 115 | <li>
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| 116 | <p><userinput>kg</userinput>, <userinput>kh</userinput>, and
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| 117 | <userinput>k</userinput>: Print the guest, hypervisor, and
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| 118 | current call stack
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| 119 | </p>
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| 120 | </li>
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| 121 | <li>
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| 122 | <p><userinput>da</userinput>, <userinput>db</userinput>,
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| 123 | <userinput>dw</userinput>, <userinput>dd</userinput>,
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| 124 | <userinput>dq</userinput>: Print memory contents as ASCII,
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| 125 | bytes, words, dwords, and qwords
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| 126 | </p>
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| 127 | </li>
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| 128 | <li>
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| 129 | <p><userinput>u</userinput>: Unassemble memory
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| 130 | </p>
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| 131 | </li>
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| 132 | <li>
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| 133 | <p><userinput>dg</userinput>: Print the guest's GDT
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| 134 | </p>
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| 135 | </li>
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| 136 | <li>
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| 137 | <p><userinput>di</userinput>: Print the guest's IDT
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| 138 | </p>
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| 139 | </li>
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| 140 | <li>
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| 141 | <p><userinput>dl</userinput>: Print the guest's LDT
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| 142 | </p>
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| 143 | </li>
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| 144 | <li>
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| 145 | <p><userinput>dt</userinput>: Print the guest's TSS
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| 146 | </p>
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| 147 | </li>
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| 148 | <li>
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| 149 | <p><userinput>dp*</userinput>: Print the guest's page table
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| 150 | structures
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| 151 | </p>
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| 152 | </li>
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| 153 | <li>
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| 154 | <p><userinput>bp</userinput> and <userinput>br</userinput>: Set a
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| 155 | normal and recompiler breakpoint
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| 156 | </p>
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| 157 | </li>
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| 158 | <li>
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| 159 | <p><userinput>bl</userinput>: List breakpoints
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| 160 | </p>
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| 161 | </li>
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| 162 | <li>
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| 163 | <p><userinput>bc</userinput>: Clear a breakpoint
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| 164 | </p>
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| 165 | </li>
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| 166 | <li>
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| 167 | <p><userinput>writecore</userinput>: Write a VM core file to disk.
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| 168 | See <xref href="ts_guest-core-format.dita#ts_guest-core-format"/></p>
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| 169 | </li>
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| 170 | </ul>
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| 171 | <p>
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| 172 | See the built-in <userinput>help</userinput> for other available
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| 173 | commands.
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| 174 | </p>
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| 175 | <p>
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| 176 | The VM debugger supports symbolic debugging, although symbols
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| 177 | for guest code are often not available. For Oracle Solaris
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| 178 | guests, the <userinput>detect</userinput> command automatically
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| 179 | determines the guest OS version and locates kernel symbols in
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| 180 | guest's memory. Symbolic debugging is then available. For Linux
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| 181 | guests, the <userinput>detect</userinput> commands also determines
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| 182 | the guest OS version, but there are no symbols in the guest's
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| 183 | memory. Kernel symbols are available in the file
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| 184 | <filepath>/proc/kallsyms</filepath> on Linux guests. This file
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| 185 | must be copied to the host, for example using
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| 186 | <userinput>scp</userinput>. The <userinput>loadmap</userinput> debugger
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| 187 | command can be used to make the symbol information available to
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| 188 | the VM debugger. Note that the <filepath>kallsyms</filepath>
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| 189 | file contains the symbols for the currently loaded modules. If
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| 190 | the guest's configuration changes, the symbols will change as
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| 191 | well and must be updated.
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| 192 | </p>
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| 193 | <p>
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| 194 | For all guests, a simple way to verify that the correct symbols
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| 195 | are loaded is the <userinput>k</userinput> command. The guest is
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| 196 | normally idling and it should be clear from the symbolic
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| 197 | information that the guest operating system's idle loop is being
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| 198 | executed.
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| 199 | </p>
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| 200 | <p>
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| 201 | Another group of debugger commands is the set of
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| 202 | <userinput>info</userinput> commands. Running <userinput>info
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| 203 | help</userinput> provides complete usage information. The
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| 204 | information commands provide ad-hoc data pertinent to various
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| 205 | emulated devices and aspects of the VMM. There is no general
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| 206 | guideline for using the <userinput>info</userinput> commands, the
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| 207 | right command to use depends entirely on the problem being
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| 208 | investigated. Some of the <userinput>info</userinput> commands are
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| 209 | as follows:
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| 210 | </p>
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| 211 | <ul>
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| 212 | <li>
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| 213 | <p><userinput>cfgm</userinput>: Print a branch of the configuration
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| 214 | tree
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| 215 | </p>
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| 216 | </li>
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| 217 | <li>
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| 218 | <p><userinput>cpuid</userinput>: Display the guest CPUID leaves
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| 219 | </p>
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| 220 | </li>
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| 221 | <li>
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| 222 | <p><userinput>ioport</userinput>: Print registered I/O port ranges
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| 223 | </p>
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| 224 | </li>
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| 225 | <li>
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| 226 | <p><userinput>mmio</userinput>: Print registered MMIO ranges
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| 227 | </p>
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| 228 | </li>
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| 229 | <li>
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| 230 | <p><userinput>mode</userinput>: Print the current paging mode
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| 231 | </p>
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| 232 | </li>
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| 233 | <li>
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| 234 | <p><userinput>pit</userinput>: Print the i8254 PIT state
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| 235 | </p>
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| 236 | </li>
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| 237 | <li>
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| 238 | <p><userinput>pic</userinput>: Print the i8259A PIC state
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| 239 | </p>
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| 240 | </li>
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| 241 | <li>
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| 242 | <p><userinput>ohci</userinput>, <userinput>ehci</userinput>,
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| 243 | <userinput>xhci</userinput>: Print a subset of the OHCI, EHCI,
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| 244 | and xHCI USB controller state
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| 245 | </p>
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| 246 | </li>
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| 247 | <li>
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| 248 | <p><userinput>pcnet0</userinput>: Print the PCnet state
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| 249 | </p>
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| 250 | </li>
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| 251 | <li>
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| 252 | <p><userinput>vgatext</userinput>: Print the contents of the VGA
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| 253 | framebuffer formatted as standard text mode
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| 254 | </p>
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| 255 | </li>
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| 256 | <li>
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| 257 | <p><userinput>timers</userinput>: Print all VM timers
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| 258 | </p>
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| 259 | </li>
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| 260 | </ul>
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| 261 | <p>
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| 262 | The output of the <userinput>info</userinput> commands generally
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| 263 | requires in-depth knowledge of the emulated device or
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| 264 | Oracle VM VirtualBox VMM internals. However, when used properly, the
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| 265 | information provided can be invaluable.
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| 266 | </p>
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| 267 | </body>
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| 268 |
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| 269 | </topic>
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