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Line 1: ~~{{Tone}}~~ {{Emulators}} QEMU is a free and open-source emulator that performs hardware virtualization. It is widely available for variety of host operating-systems and requires minimal configuration for use in operating-system development. It is capable of emulating a wide variety of systems including [[ARM]], [[x86]] and [[RISC-V]], among others. For a more comprehensive list of targets refer to the [https://www.qemu.~~weilnetz.de~~org/~~doc~~docs/master/~~qemu-doc.html~~ official documentation]. Line 113 ⟶ 112: * PCI SVGA card (Cirrus Logic 5446) * PCI support (With BIOS32). * [[QEMU_fw_cfg]] Allows you to pass info to the guest ==Usage== Line 118: QEMU does not require the use of a configuration script like Bochs. An example usage of QEMU can be seen below: <~~source~~syntaxhighlight lang="bash"> qemu-system-i386 \ -accel tcg,thread=single \ Line 129: -usb \ -vga std </syntaxhighlight> ~~</source>~~ When running QEMU on a non-UNIX system, it may be necessary to use the <tt>-L</tt> command-line option to instruct QEMU where to find a BIOS image. Line 135: The <tt>-m 128</tt> argument instructs QEMU to create the guest system with 128MB of RAM. The <tt>-drive format=raw,media=cdrom,file=myos.iso</tt> argument instructs QEMU to create a drive in our guest system. In this case the created drive is a CDROM drive, with <tt>myos.iso</tt> as its loaded media. If more than one drive in is required in the guest system, it is possible to use the <tt>-boot</tt> option to define the order in which the system will check for bootable media. The <tt>-serial stdio</tt> argument used above instructs QEMU to redirect the serial input and output to the host system's <tt>stdio</tt> stream. This is particularly useful for debugging purposes. In the documentation, the option to redirect this to <tt>stdio</tt> is described as Unix only. Presumably, one should be able to achieve a similar effect with <tt>-serial file:CON</tt> on Windows. In order to help track down the source of a triple fault, the <tt>-d int</tt> option can be used to show additional debugging information on interrupts that occur. Additionally, the <tt>-no-shutdown</tt> and <tt>-no-reboot</tt> options can be used. These instruct the virtual machine to halt on error instead of rebooting or shutting down, allowing for the operator to inspect the state of the machine after a triple-fault. Additional useful command-line options are listed within the [[QEMU#Useful_QEMU_command-line_options\|Useful QEMU command-line options]] section. The keyboard shortcuts <tt>CTRL-ALT-{1,2,3}</tt> can be used inside the emulator to swap in/out of the emulation screen, the QEMU console and a serial console. Additional debugging commands can be issued from the system console, such as changing disk images and performing memory dumps, among others.▼ ▲The keyboard shortcuts <tt>CTRL-ALT-{1,2,3}</tt> can be used inside the emulator to swap in/out of the emulation screen, the QEMU ~~console~~monitor and a serial console. Additional debugging commands can be issued from the system console, such as changing disk images and performing memory dumps, among others. ===The QEMU Console===▼ ▲===The ~~QEMU~~debug ~~Console~~console=== ~~QEMU's internal console can be accessed by the key combination CTRL-ALT-3 within QEMU.~~ Instead of the serial port, as outlined above, one can also use the <tt>debugcon</tt> device. By running QEMU with <tt>-debugcon stdio</tt>, you can print a message to your host system's terminal by just writing each byte to port 0xe9. This is the same port as the one used by [[Bochs#I/O_debugger_macros\|the equivalent feature in Bochs]]. Unlike [[Bochs]], QEMU does not provide an [[Port IO\|IO port]] for communicating directly with its internal console. Output to the internal console can be accomplished by the redirection of serial output. Using the following command-line option will redirect COM1's output to the QEMU console: ~~<source lang="bash">~~ Unlike the serial port, the debug console is one-way – you can only output. On the flip side, implementing support is much easier, and outputting the messages isn't artificially throttled by a baudrate. ~~-serial file:CON~~ ~~</source>~~ ===The QEMU monitor=== {{Main\|QEMU Monitor}} QEMU features its own internal 'monitor' console for debugging the guest operating-system. Through various commands, the monitor allows you to inspect the running guest OS, change removable media and USB devices, take screenshots and audio grabs, and control various aspects of the virtual machine. The monitor can be accessed by the key combination <tt>CTRL-ALT-2</tt> within QEMU. ~~If you are running QEMU from the command-line, it~~It is possible to redirect QEMU's monitor output to stdio using the following command -line option when invoking QEMU: <~~source~~syntaxhighlight lang="bash"> -monitor stdio </syntaxhighlight> ~~</source>~~ Line 202 ⟶ 204: For convenience, it is also possible to create a file containing commands for GDB to automatically execute. GDB will read and execute the contents of a file with the name <tt>.gdbinit</tt> in the current working directory. Alternatively, a different file may be specified by the use the <tt>-command=file</tt> command-line argument. An example file can be seen below: <~~source~~!-- lang="gdb" Avoid highlighting errors --> <syntaxhighlight lang="text"> file <my-kernel-binary> target remote localhost:1234 Line 208 ⟶ 211: # Inspect page tables x /8wg &page_tables_start </syntaxhighlight> ~~</source>~~ This will automatically load the kernel binary's symbol file into the debugger and then open the remote connection to QEMU.<br/> Ensure that the kernel was compiled with debugging symbols included. This can be accomplished via the use of the GCC option <tt>-g</tt>. If you find that the debugger can't find local variables, try using the <tt>-fno-omit-frame-pointer</tt> option during compilation, or disable optimizations. IfWhen ~~you have~~running an SMP kernel, ~~check out~~ the <tt>info threads</tt> and <tt>thread</tt> commands can be used to provide useful information. It is also possible to use the QEMU monitor and its commands using the <tt>monitor</tt> command in GDB. For a list of available commands and their description, ~~check~~use ~~out~~the <tt>monitor help</tt> command. ==Getting detailed logs== Line 220 ⟶ 223: Some files within the QEMU source code have commented lines of the form: <~~source~~syntaxhighlight lang="c"> // #define DEBUG_* </syntaxhighlight> ~~</source>~~ Recompiling QEMU from source with this preprocessor variable defined will cause additional debugging information from the applicable file to be printed to stdout. Line 235 ⟶ 238: [http://www.qemu.org/ QEMU homepage] [http://qemu-forum.ipi.fi/ QEMU forum] [https://en.wikibooks.org/wiki/QEMU QEMU Wikibook] [https://wiki.archlinux.org/index.php/QEMU#Creating_a_hard_disk_image QEMU at ArchWiki] [[Category:Emulators]] [[Category:QEMU]] [[de:QEMU]]