# QEMU CPU Emulator User Documentation

# Table of Contents

- 1. Introduction
  - 1.1 Features
- 2. Installation
  - 2.1 Linux
  - 2.2 Windows
  - 2.3 Mac OS X
- 3. QEMU PC System emulator invocation
  - 3.1 Introduction
  - 3.2 Quick Start
  - 3.3 Invocation
  - 3.4 Keys
  - 3.5 QEMU Monitor
    - 3.5.1 Commands
    - 3.5.2 Integer expressions
  - 3.6 Disk Images
    - 3.6.1 Quick start for disk image creation
    - 3.6.2 Snapshot mode
    - 3.6.3 `qemu-img` Invocation
  - 3.7 Network emulation
    - 3.7.1 Using tun/tap network interface
    - 3.7.2 Using the user mode network stack
  - 3.8 Direct Linux Boot
  - 3.9 Linux Kernel Compilation
  - 3.10 GDB usage
  - 3.11 Target OS specific information
    - 3.11.1 Linux
    - 3.11.2 Windows
      - 3.11.2.1 SVGA graphic modes support
      - 3.11.2.2 CPU usage reduction
      - 3.11.2.3 Windows 2000 disk full problems
      - 3.11.2.4 Windows XP security problems
    - 3.11.3 MS-DOS and FreeDOS
      - 3.11.3.1 CPU usage reduction
- 4. QEMU PowerPC System emulator invocation
- 5. QEMU User space emulator invocation
  - 5.1 Quick Start
  - 5.2 Wine launch
  - 5.3 Command line options
- 6. Compilation from the sources
  - 6.1 Linux/BSD
  - 6.2 Windows
  - 6.3 Cross compilation for Windows with Linux
  - 6.4 Mac OS X

QEMU CPU Emulator User Documentation

# 1. Introduction

## 1.1 Features

QEMU is a FAST! processor emulator using dynamic translation to achieve good emulation speed.

QEMU has two operating modes:

- Full system emulation. In this mode, QEMU emulates a full system (for example a PC), including a processor and various peripherials. It can be used to launch different Operating Systems without rebooting the PC or to debug system code.
- User mode emulation (Linux host only). In this mode, QEMU can launch Linux processes compiled for one CPU on another CPU. It can be used to launch the Wine Windows API emulator (http://www.winehq.org) or to ease cross-compilation and cross-debugging.

As QEMU requires no host kernel driver to run, it is very safe and easy to use.

For system emulation, the following hardware targets are supported:

- PC (x86 processor)
- PREP (PowerPC processor)
- PowerMac (PowerPC processor, in progress)

For user emulation, x86, PowerPC, ARM, and SPARC CPUs are supported.

# 2. Installation

If you want to compile QEMU yourself, see section 6. Compilation from the sources.

## 2.1 Linux

Download the binary distribution (``qemu-XXX-i386.tar.gz'`) and untar it as root in ``/'`:

    su
    cd /
    tar zxvf /tmp/qemu-XXX-i386.tar.gz

## 2.2 Windows

Download the experimental binary installer at http://www.freeoszoo.org/download.php.

## 2.3 Mac OS X

Download the experimental binary installer at http://www.freeoszoo.org/download.php.

# 3. QEMU PC System emulator invocation

## 3.1 Introduction

The QEMU System emulator simulates a complete PC.

In order to meet specific user needs, two versions of QEMU are available:

1. `qemu-fast` uses the host Memory Management Unit (MMU) to simulate the x86 MMU. It is fast but has limitations because the whole 4 GB address space cannot be used and some memory mapped peripherials cannot be emulated accurately yet. Therefore, a specific guest Linux kernel can be used (See section 3.9 Linux Kernel Compilation) as guest OS. Moreover there is no separation between the host and target address spaces, so it offers no security (the target OS can modify the `qemu-fast` code by writing at the right addresses).
2. `qemu` uses a software MMU. It is about two times slower but gives a more accurate emulation and a complete separation between the host and target address spaces.

QEMU emulates the following PC peripherials:

- i440FX host PCI bridge and PIIX3 PCI to ISA bridge
- Cirrus CLGD 5446 PCI VGA card or dummy VGA card with Bochs VESA extensions (hardware level, including all non standard modes).
- PS/2 mouse and keyboard
- 2 PCI IDE interfaces with hard disk and CD-ROM support
- Floppy disk
- NE2000 PCI network adapters
- Serial ports
- Soundblaster 16 card

QEMU uses the PC BIOS from the Bochs project and the Plex86/Bochs LGPL VGA BIOS.

## 3.2 Quick Start

Download and uncompress the linux image (``linux.img'`) and type:

    qemu linux.img

Linux should boot and give you a prompt.

## 3.3 Invocation

    usage: qemu [options] [disk_image]

disk_image is a raw hard disk image for IDE hard disk 0.

General options:

``-fda file'`
``-fdb file'`
  Use file as floppy disk 0/1 image (See section 3.6 Disk Images). You can use the host floppy by using ``/dev/fd0'` as filename.
``-hda file'`
``-hdb file'`
``-hdc file'`
``-hdd file'`
  Use file as hard disk 0, 1, 2 or 3 image (See section 3.6 Disk Images).
``-cdrom file'`
  Use file as CD-ROM image (you cannot use ``-hdc'` and and ``-cdrom'` at the same time). You can use the host CD-ROM by using ``/dev/cdrom'` as filename.
``-boot [a|c|d]'`
  Boot on floppy (a), hard disk (c) or CD-ROM (d). Hard disk boot is the default.
``-snapshot'`
  Write to temporary files instead of disk image files. In this case, the raw disk image you use is not written back. You can however force the write back by pressing `C-a s` (See section 3.6 Disk Images).
``-m megs'`
  Set virtual RAM size to megs megabytes. Default is 128 MB.
``-nographic'`
  Normally, QEMU uses SDL to display the VGA output. With this option, you can totally disable graphical output so that QEMU is a simple command line application. The emulated serial port is redirected on the console. Therefore, you can still use QEMU to debug a Linux kernel with a serial console.
``-enable-audio'`
  The SB16 emulation is disabled by default as it may give problems with Windows. You can enable it manually with this option.
``-localtime'`
  Set the real time clock to local time (the default is to UTC time). This option is needed to have correct date in MS-DOS or Windows.
``-full-screen'`
  Start in full screen.

Network options:

``-n script'`
  Set TUN/TAP network init script [default=/etc/qemu-ifup]. This script is launched to configure the host network interface (usually tun0) corresponding to the virtual NE2000 card.
``-macaddr addr'`
  Set the mac address of the first interface (the format is aa:bb:cc:dd:ee:ff in hexa). The mac address is incremented for each new network interface.
``-tun-fd fd'`
  Assumes fd talks to a tap/tun host network interface and use it. Read http://bellard.org/qemu/tetrinet.html to have an example of its use.
``-user-net'`
  Use the user mode network stack. This is the default if no tun/tap network init script is found.
``-tftp prefix'`
  When using the user mode network stack, activate a built-in TFTP server. All filenames beginning with prefix can be downloaded from the host to the guest using a TFTP client. The TFTP client on the guest must be configured in binary mode (use the command `bin` of the Unix TFTP client). The host IP address on the guest is as usual 10.0.2.2.
``-smb dir'`
  When using the user mode network stack, activate a built-in SMB server so that Windows OSes can access to the host files in ``dir'` transparently. In the guest Windows OS, the line:

      10.0.2.4 smbserver

  must be added in the file ``C:\WINDOWS\LMHOSTS'` (for windows 9x/Me) or ``C:\WINNT\SYSTEM32\DRIVERS\ETC\LMHOSTS'` (Windows NT/2000). Then ``dir'` can be accessed in ``\\smbserver\qemu'`. Note that a SAMBA server must be installed on the host OS in ``/usr/sbin/smbd'`. QEMU was tested succesfully with smbd version 2.2.7a from the Red Hat 9.
``-redir [tcp|udp]:host-port:[guest-host]:guest-port'`
  When using the user mode network stack, redirect incoming TCP or UDP connections to the host port host-port to the guest guest-host on guest port guest-port. If guest-host is not specified, its value is 10.0.2.15 (default address given by the built-in DHCP server). For example, to redirect host X11 connection from screen 1 to guest screen 0, use the following:

      # on the host
      qemu -redir tcp:6001::6000 [...]
      # this host xterm should open in the guest X11 server
      xterm -display :1

  To redirect telnet connections from host port 5555 to telnet port on the guest, use the following:

      # on the host
      qemu -redir tcp:5555::23 [...]
      telnet localhost 5555

  Then when you use on the host `telnet localhost 5555`, you connect to the guest telnet server.
``-dummy-net'`
  Use the dummy network stack: no packet will be received by the network cards.

Linux boot specific. When using this options, you can use a given Linux kernel without installing it in the disk image. It can be useful for easier testing of various kernels.

``-kernel bzImage'`
  Use bzImage as kernel image.
``-append cmdline'`
  Use cmdline as kernel command line
``-initrd file'`
  Use file as initial ram disk.

Debug/Expert options:

``-serial dev'`
  Redirect the virtual serial port to host device dev. Available devices are:
  `vc`
    Virtual console
  `pty`
    [Linux only] Pseudo TTY (a new PTY is automatically allocated)
  `null`
    void device
  `stdio`
    [Unix only] standard input/output
  The default device is `vc` in graphical mode and `stdio` in non graphical mode. This option can be used several times to simulate up to 4 serials ports.
``-monitor dev'`
  Redirect the monitor to host device dev (same devices as the serial port). The default device is `vc` in graphical mode and `stdio` in non graphical mode.
``-s'`
  Wait gdb connection to port 1234 (See section 3.10 GDB usage).
``-p port'`
  Change gdb connection port.
``-S'`
  Do not start CPU at startup (you must type 'c' in the monitor).
``-d'`
  Output log in /tmp/qemu.log
``-isa'`
  Simulate an ISA-only system (default is PCI system).
``-std-vga'`
  Simulate a standard VGA card with Bochs VBE extensions (default is Cirrus Logic GD5446 PCI VGA)
``-loadvm file'`
  Start right away with a saved state (`loadvm` in monitor)

## 3.4 Keys

During the graphical emulation, you can use the following keys:

`Ctrl-Alt-f`
  Toggle full screen
`Ctrl-Alt-n`
  Switch to virtual console 'n'. Standard console mappings are:
  1
    Target system display
  2
    Monitor
  3
    Serial port
`Ctrl-Alt`
  Toggle mouse and keyboard grab.

In the virtual consoles, you can use `Ctrl-Up`, `Ctrl-Down`, `Ctrl-PageUp` and `Ctrl-PageDown` to move in the back log.

During emulation, if you are using the ``-nographic'` option, use `Ctrl-a h` to get terminal commands:

`Ctrl-a h`
  Print this help
`Ctrl-a x`
  Exit emulatior
`Ctrl-a s`
  Save disk data back to file (if -snapshot)
`Ctrl-a b`
  Send break (magic sysrq in Linux)
`Ctrl-a c`
  Switch between console and monitor
`Ctrl-a Ctrl-a`
  Send Ctrl-a

## 3.5 QEMU Monitor

The QEMU monitor is used to give complex commands to the QEMU emulator. You can use it to:

- Remove or insert removable medias images (such as CD-ROM or floppies)
- Freeze/unfreeze the Virtual Machine (VM) and save or restore its state from a disk file.
- Inspect the VM state without an external debugger.

### 3.5.1 Commands

The following commands are available:

``help or ? [cmd]'`
  Show the help for all commands or just for command cmd.
``commit'`
  Commit changes to the disk images (if -snapshot is used)
``info subcommand'`
  show various information about the system state
  ``info network'`
    show the network state
  ``info block'`
    show the block devices
  ``info registers'`
    show the cpu registers
  ``info history'`
    show the command line history
``q or quit'`
  Quit the emulator.
``eject [-f] device'`
  Eject a removable media (use -f to force it).
``change device filename'`
  Change a removable media.
``screendump filename'`
  Save screen into PPM image filename.
``log item1[,...]'`
  Activate logging of the specified items to ``/tmp/qemu.log'`.
``savevm filename'`
  Save the whole virtual machine state to filename.
``loadvm filename'`
  Restore the whole virtual machine state from filename.
``stop'`
  Stop emulation.
``c or cont'`
  Resume emulation.
``gdbserver [port]'`
  Start gdbserver session (default port=1234)
``x/fmt addr'`
  Virtual memory dump starting at addr.
``xp /fmt addr'`
  Physical memory dump starting at addr. fmt is a format which tells the command how to format the data. Its syntax is: ``/{count}{format}{size}'`
  count
    is the number of items to be dumped.
  format
    can be x (hexa), d (signed decimal), u (unsigned decimal), o (octal), c (char) or i (asm instruction).
  size
    can be b (8 bits), h (16 bits), w (32 bits) or g (64 bits). On x86, `h` or `w` can be specified with the `i` format to respectively select 16 or 32 bit code instruction size.
  Examples:
  - Dump 10 instructions at the current instruction pointer:

        (qemu) x/10i $eip
        0x90107063:  ret
        0x90107064:  sti
        0x90107065:  lea    0x0(%esi,1),%esi
        0x90107069:  lea    0x0(%edi,1),%edi
        0x90107070:  ret
        0x90107071:  jmp    0x90107080
        0x90107073:  nop
        0x90107074:  nop
        0x90107075:  nop
        0x90107076:  nop

  - Dump 80 16 bit values at the start of the video memory.

        (qemu) xp/80hx 0xb8000
        0x000b8000: 0x0b50 0x0b6c 0x0b65 0x0b78 0x0b38 0x0b36 0x0b2f 0x0b42
        0x000b8010: 0x0b6f 0x0b63 0x0b68 0x0b73 0x0b20 0x0b56 0x0b47 0x0b41
        0x000b8020: 0x0b42 0x0b69 0x0b6f 0x0b73 0x0b20 0x0b63 0x0b75 0x0b72
        0x000b8030: 0x0b72 0x0b65 0x0b6e 0x0b74 0x0b2d 0x0b63 0x0b76 0x0b73
        0x000b8040: 0x0b20 0x0b30 0x0b35 0x0b20 0x0b4e 0x0b6f 0x0b76 0x0b20
        0x000b8050: 0x0b32 0x0b30 0x0b30 0x0b33 0x0720 0x0720 0x0720 0x0720
        0x000b8060: 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720
        0x000b8070: 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720
        0x000b8080: 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720
        0x000b8090: 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720 0x0720

``p or print/fmt expr'`
  Print expression value. Only the format part of fmt is used.
``sendkey keys'`
  Send keys to the emulator. Use `-` to press several keys simultaneously. Example:

      sendkey ctrl-alt-f1

  This command is useful to send keys that your graphical user interface intercepts at low level, such as `ctrl-alt-f1` in X Window.
``system_reset'`
  Reset the system.

### 3.5.2 Integer expressions

The monitor understands integers expressions for every integer argument. You can use register names to get the value of specifics CPU registers by prefixing them with $.

## 3.6 Disk Images

Since version 0.6.1, QEMU supports many disk image formats, including growable disk images (their size increase as non empty sectors are written), compressed and encrypted disk images.

### 3.6.1 Quick start for disk image creation

You can create a disk image with the command:

    qemu-img create myimage.img mysize

where myimage.img is the disk image filename and mysize is its size in kilobytes. You can add an `M` suffix to give the size in megabytes and a `G` suffix for gigabytes.

See section 3.6.3 `qemu-img` Invocation for more information.

### 3.6.2 Snapshot mode

If you use the option ``-snapshot'`, all disk images are considered as read only. When sectors in written, they are written in a temporary file created in ``/tmp'`. You can however force the write back to the raw disk images by using the `commit` monitor command (or `C-a s` in the serial console).

### 3.6.3 `qemu-img` Invocation

    usage: qemu-img command [command options]

The following commands are supported:

``create [-e] [-b base_image] [-f fmt] filename [size]'`
``commit [-f fmt] filename'`
``convert [-c] [-e] [-f fmt] filename [-O output_fmt] output_filename'`
``info [-f fmt] filename'`

Command parameters:

filename
  is a disk image filename
base_image
  is the read-only disk image which is used as base for a copy on write image; the copy on write image only stores the modified data
fmt
  is the disk image format. It is guessed automatically in most cases. The following formats are supported:
  `raw`
    Raw disk image format (default). This format has the advantage of being simple and easily exportable to all other emulators. If your file system supports holes (for example in ext2 or ext3 on Linux), then only the written sectors will reserve space. Use `qemu-img info` to know the real size used by the image or `ls -ls` on Unix/Linux.
  `qcow`
    QEMU image format, the most versatile format. Use it to have smaller images (useful if your filesystem does not supports holes, for example on Windows), optional AES encryption and zlib based compression.
  `cow`
    User Mode Linux Copy On Write image format. Used to be the only growable image format in QEMU. It is supported only for compatibility with previous versions. It does not work on win32.
  `vmdk`
    VMware 3 and 4 compatible image format. Currently only supported as read-only.
  `cloop`
    Linux Compressed Loop image, useful only to reuse directly compressed CD-ROM images present for example in the Knoppix CD-ROMs.
size
  is the disk image size in kilobytes. Optional suffixes `M` (megabyte) and `G` (gigabyte) are supported
output_filename
  is the destination disk image filename
output_fmt
  is the destination format
-c
  indicates that target image must be compressed (qcow format only)
-e
  indicates that the target image must be encrypted (qcow format only)

Command description:

``create [-e] [-b base_image] [-f fmt] filename [size]'`
  Create the new disk image filename of size size and format fmt. If base_image is specified, then the image will record only the differences from base_image. No size needs to be specified in this case. base_image will never be modified unless you use the `commit` monitor command.
``commit [-f fmt] filename'`
  Commit the changes recorded in filename in its base image.
``convert [-c] [-e] [-f fmt] filename [-O output_fmt] output_filename'`
  Convert the disk image filename to disk image output_filename using format output_fmt. It can be optionnaly encrypted (`-e` option) or compressed (`-c` option). Only the format `qcow` supports encryption or compression. The compression is read-only. It means that if a compressed sector is rewritten, then it is rewritten as uncompressed data. Encryption uses the AES format which is very secure (128 bit keys). Use a long password (16 characters) to get maximum protection. Image conversion is also useful to get smaller image when using a growable format such as `qcow` or `cow`: the empty sectors are detected and suppressed from the destination image.
``info [-f fmt] filename'`
  Give information about the disk image filename. Use it in particular to know the size reserved on disk which can be different from the displayed size.

## 3.7 Network emulation

QEMU simulates up to 6 networks cards (NE2000 boards). Each card can be connected to a specific host network interface.

### 3.7.1 Using tun/tap network interface

This is the standard way to emulate network. QEMU adds a virtual network device on your host (called `tun0`), and you can then configure it as if it was a real ethernet card.

As an example, you can download the ``linux-test-xxx.tar.gz'` archive and copy the script ``qemu-ifup'` in ``/etc'` and configure properly `sudo` so that the command `ifconfig` contained in ``qemu-ifup'` can be executed as root. You must verify that your host kernel supports the TUN/TAP network interfaces: the device ``/dev/net/tun'` must be present.

See section 3.8 Direct Linux Boot to have an example of network use with a Linux distribution.

### 3.7.2 Using the user mode network stack

By using the option ``-user-net'` or if you have no tun/tap init script, QEMU uses a completely user mode network stack (you don't need root priviledge to use the virtual network). The virtual network configuration is the following:

    QEMU Virtual Machine    <------>  Firewall/DHCP server <-----> Internet
         (10.0.2.x)            |          (10.0.2.2)
                               |
                               ---->  DNS server (10.0.2.3)
                               |
                               ---->  SMB server (10.0.2.4)

The QEMU VM behaves as if it was behind a firewall which blocks all incoming connections. You can use a DHCP client to automatically configure the network in the QEMU VM.

In order to check that the user mode network is working, you can ping the address 10.0.2.2 and verify that you got an address in the range 10.0.2.x from the QEMU virtual DHCP server.

Note that `ping` is not supported reliably to the internet as it would require root priviledges. It means you can only ping the local router (10.0.2.2).

When using the built-in TFTP server, the router is also the TFTP server.

When using the ``-redir'` option, TCP or UDP connections can be redirected from the host to the guest. It allows for example to redirect X11, telnet or SSH connections.

## 3.8 Direct Linux Boot

This section explains how to launch a Linux kernel inside QEMU without having to make a full bootable image. It is very useful for fast Linux kernel testing. The QEMU network configuration is also explained.

1. Download the archive ``linux-test-xxx.tar.gz'` containing a Linux kernel and a disk image.
2. Optional: If you want network support (for example to launch X11 examples), you must copy the script ``qemu-ifup'` in ``/etc'` and configure properly `sudo` so that the command `ifconfig` contained in ``qemu-ifup'` can be executed as root. You must verify that your host kernel supports the TUN/TAP network interfaces: the device ``/dev/net/tun'` must be present. When network is enabled, there is a virtual network connection between the host kernel and the emulated kernel. The emulated kernel is seen from the host kernel at IP address 172.20.0.2 and the host kernel is seen from the emulated kernel at IP address 172.20.0.1.
3. Launch `qemu.sh`. You should have the following output:

       > ./qemu.sh
       Connected to host network interface: tun0
       Linux version 2.4.21 (bellard@voyager.localdomain) (gcc version 3.2.2 20030222 (Red Hat Linux 3.2.2-5)) #5 Tue Nov 11 18:18:53 CET 2003
       BIOS-provided physical RAM map:
        BIOS-e801: 0000000000000000 - 000000000009f000 (usable)
        BIOS-e801: 0000000000100000 - 0000000002000000 (usable)
       32MB LOWMEM available.
       On node 0 totalpages: 8192
       zone(0): 4096 pages.
       zone(1): 4096 pages.
       zone(2): 0 pages.
       Kernel command line: root=/dev/hda sb=0x220,5,1,5 ide2=noprobe ide3=noprobe ide4=noprobe ide5=noprobe console=ttyS0
       ide_setup: ide2=noprobe
       ide_setup: ide3=noprobe
       ide_setup: ide4=noprobe
       ide_setup: ide5=noprobe
       Initializing CPU#0
       Detected 2399.621 MHz processor.
       Console: colour EGA 80x25
       Calibrating delay loop... 4744.80 BogoMIPS
       Memory: 28872k/32768k available (1210k kernel code, 3508k reserved, 266k data, 64k init, 0k highmem)
       Dentry cache hash table entries: 4096 (order: 3, 32768 bytes)
       Inode cache hash table entries: 2048 (order: 2, 16384 bytes)
       Mount cache hash table entries: 512 (order: 0, 4096 bytes)
       Buffer-cache hash table entries: 1024 (order: 0, 4096 bytes)
       Page-cache hash table entries: 8192 (order: 3, 32768 bytes)
       CPU: Intel Pentium Pro stepping 03
       Checking 'hlt' instruction... OK.
       POSIX conformance testing by UNIFIX
       Linux NET4.0 for Linux 2.4
       Based upon Swansea University Computer Society NET3.039
       Initializing RT netlink socket
       apm: BIOS not found.
       Starting kswapd
       Journalled Block Device driver loaded
       Detected PS/2 Mouse Port.
       pty: 256 Unix98 ptys configured
       Serial driver version 5.05c (2001-07-08) with no serial options enabled
       ttyS00 at 0x03f8 (irq = 4) is a 16450
       ne.c:v1.10 9/23/94 Donald Becker (becker@scyld.com)
       Last modified Nov 1, 2000 by Paul Gortmaker
       NE*000 ethercard probe at 0x300: 52 54 00 12 34 56
       eth0: NE2000 found at 0x300, using IRQ 9.
       RAMDISK driver initialized: 16 RAM disks of 4096K size 1024 blocksize
       Uniform Multi-Platform E-IDE driver Revision: 7.00beta4-2.4
       ide: Assuming 50MHz system bus speed for PIO modes; override with idebus=xx
       hda: QEMU HARDDISK, ATA DISK drive
       ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
       hda: attached ide-disk driver.
       hda: 20480 sectors (10 MB) w/256KiB Cache, CHS=20/16/63
       Partition check:
        hda:
       Soundblaster audio driver Copyright (C) by Hannu Savolainen 1993-1996
       NET4: Linux TCP/IP 1.0 for NET4.0
       IP Protocols: ICMP, UDP, TCP, IGMP
       IP: routing cache hash table of 512 buckets, 4Kbytes
       TCP: Hash tables configured (established 2048 bind 4096)
       NET4: Unix domain sockets 1.0/SMP for Linux NET4.0.
       EXT2-fs warning: mounting unchecked fs, running e2fsck is recommended
       VFS: Mounted root (ext2 filesystem).
       Freeing unused kernel memory: 64k freed

       Linux version 2.4.21 (bellard@voyager.localdomain) (gcc version 3.2.2 20030222 (Red Hat Linux 3.2.2-5)) #5 Tue Nov 11 18:18:53 CET 2003

       QEMU Linux test distribution (based on Redhat 9)

       Type 'exit' to halt the system

       sh-2.05b#

4. Then you can play with the kernel inside the virtual serial console. You can launch `ls` for example. Type `Ctrl-a h` to have an help about the keys you can type inside the virtual serial console. In particular, use `Ctrl-a x` to exit QEMU and use `Ctrl-a b` as the Magic SysRq key.
5. If the network is enabled, launch the script ``/etc/linuxrc'` in the emulator (don't forget the leading dot):

       . /etc/linuxrc

   Then enable X11 connections on your PC from the emulated Linux:

       xhost +172.20.0.2

   You can now launch ``xterm'` or ``xlogo'` and verify that you have a real Virtual Linux system !

NOTES:

1. A 2.5.74 kernel is also included in the archive. Just replace the bzImage in qemu.sh to try it.
2. qemu-fast creates a temporary file in $QEMU_TMPDIR (``/tmp'` is the default) containing all the simulated PC memory. If possible, try to use a temporary directory using the tmpfs filesystem to avoid too many unnecessary disk accesses.
3. In order to exit cleanly from qemu, you can do a shutdown inside qemu. qemu will automatically exit when the Linux shutdown is done.
4. You can boot slightly faster by disabling the probe of non present IDE interfaces. To do so, add the following options on the kernel command line:

       ide1=noprobe ide2=noprobe ide3=noprobe ide4=noprobe ide5=noprobe

5. The example disk image is a modified version of the one made by Kevin Lawton for the plex86 Project (www.plex86.org).

## 3.9 Linux Kernel Compilation

You can use any linux kernel with QEMU. However, if you want to use `qemu-fast` to get maximum performances, you must use a modified guest kernel. If you are using a 2.6 guest kernel, you can use directly the patch ``linux-2.6-qemu-fast.patch'` made by Rusty Russel available in the QEMU source archive. Otherwise, you can make the following changes by hand to the Linux kernel:

1. The kernel must be mapped at 0x90000000 (the default is 0xc0000000). You must modify only two lines in the kernel source: In ``include/asm/page.h'`, replace

       #define __PAGE_OFFSET           (0xc0000000)

   by

       #define __PAGE_OFFSET           (0x90000000)

   And in ``arch/i386/vmlinux.lds'`, replace

         . = 0xc0000000 + 0x100000;

   by

         . = 0x90000000 + 0x100000;

2. If you want to enable SMP (Symmetric Multi-Processing) support, you must make the following change in ``include/asm/fixmap.h'`. Replace

       #define FIXADDR_TOP	(0xffffX000UL)

   by

       #define FIXADDR_TOP	(0xa7ffX000UL)

   (X is 'e' or 'f' depending on the kernel version). Although you can use an SMP kernel with QEMU, it only supports one CPU.
3. If you are not using a 2.6 kernel as host kernel but if you use a target 2.6 kernel, you must also ensure that the 'HZ' define is set to 100 (1000 is the default) as QEMU cannot currently emulate timers at frequencies greater than 100 Hz on host Linux systems < 2.6. In ``include/asm/param.h'`, replace:

       # define HZ		1000		/* Internal kernel timer frequency */

   by

       # define HZ		100		/* Internal kernel timer frequency */

The file config-2.x.x gives the configuration of the example kernels.

Just type

    make bzImage

As you would do to make a real kernel. Then you can use with QEMU exactly the same kernel as you would boot on your PC (in ``arch/i386/boot/bzImage'`).

## 3.10 GDB usage

QEMU has a primitive support to work with gdb, so that you can do 'Ctrl-C' while the virtual machine is running and inspect its state.

In order to use gdb, launch qemu with the '-s' option. It will wait for a gdb connection:

    > qemu -s -kernel arch/i386/boot/bzImage -hda root-2.4.20.img -append "root=/dev/hda"
    Connected to host network interface: tun0
    Waiting gdb connection on port 1234

Then launch gdb on the 'vmlinux' executable:

    > gdb vmlinux

In gdb, connect to QEMU:

    (gdb) target remote localhost:1234

Then you can use gdb normally. For example, type 'c' to launch the kernel:

    (gdb) c

Here are some useful tips in order to use gdb on system code:

1. Use `info reg` to display all the CPU registers.
2. Use `x/10i $eip` to display the code at the PC position.
3. Use `set architecture i8086` to dump 16 bit code. Then use `x/10i $cs*16+*eip` to dump the code at the PC position.

## 3.11 Target OS specific information

### 3.11.1 Linux

To have access to SVGA graphic modes under X11, use the `vesa` or the `cirrus` X11 driver. For optimal performances, use 16 bit color depth in the guest and the host OS.

When using a 2.6 guest Linux kernel, you should add the option `clock=pit` on the kernel command line because the 2.6 Linux kernels make very strict real time clock checks by default that QEMU cannot simulate exactly.

### 3.11.2 Windows

If you have a slow host, using Windows 95 is better as it gives the best speed. Windows 2000 is also a good choice.

#### 3.11.2.1 SVGA graphic modes support

QEMU emulates a Cirrus Logic GD5446 Video card. All Windows versions starting from Windows 95 should recognize and use this graphic card. For optimal performances, use 16 bit color depth in the guest and the host OS.

#### 3.11.2.2 CPU usage reduction

Windows 9x does not correctly use the CPU HLT instruction. The result is that it takes host CPU cycles even when idle. You can install the utility from http://www.user.cityline.ru/~maxamn/amnhltm.zip to solve this problem. Note that no such tool is needed for NT, 2000 or XP.

#### 3.11.2.3 Windows 2000 disk full problems

Currently (release 0.6.0) QEMU has a bug which gives a `disk full` error during installation of some releases of Windows 2000. The workaround is to stop QEMU as soon as you notice that your disk image size is growing too fast (monitor it with `ls -ls`). Then relaunch QEMU to continue the installation. If you still experience the problem, relaunch QEMU again.

Future QEMU releases are likely to correct this bug.

#### 3.11.2.4 Windows XP security problems

Some releases of Windows XP install correctly but give a security error when booting:

    A problem is preventing Windows from accurately checking the
    license for this computer. Error code: 0x800703e6.

The only known workaround is to boot in Safe mode without networking support.

Future QEMU releases are likely to correct this bug.

### 3.11.3 MS-DOS and FreeDOS

#### 3.11.3.1 CPU usage reduction

DOS does not correctly use the CPU HLT instruction. The result is that it takes host CPU cycles even when idle. You can install the utility from http://www.vmware.com/software/dosidle210.zip to solve this problem.

# 4. QEMU PowerPC System emulator invocation

Use the executable ``qemu-system-ppc'` to simulate a complete PREP or PowerMac PowerPC system.

QEMU emulates the following PowerMac peripherials:

- UniNorth PCI Bridge
- PCI VGA compatible card with VESA Bochs Extensions
- 2 PMAC IDE interfaces with hard disk and CD-ROM support
- NE2000 PCI adapters
- Non Volatile RAM
- VIA-CUDA with ADB keyboard and mouse.

QEMU emulates the following PREP peripherials:

- PCI Bridge
- PCI VGA compatible card with VESA Bochs Extensions
- 2 IDE interfaces with hard disk and CD-ROM support
- Floppy disk
- NE2000 network adapters
- Serial port
- PREP Non Volatile RAM
- PC compatible keyboard and mouse.

QEMU uses the Open Hack'Ware Open Firmware Compatible BIOS available at http://site.voila.fr/jmayer/OpenHackWare/index.htm.

You can read the qemu PC system emulation chapter to have more informations about QEMU usage.

The following options are specific to the PowerPC emulation:

``-prep'`
  Simulate a PREP system (default is PowerMAC)
``-g WxH[xDEPTH]'`
  Set the initial VGA graphic mode. The default is 800x600x15.

More information is available at http://jocelyn.mayer.free.fr/qemu-ppc/.

# 5. QEMU User space emulator invocation

## 5.1 Quick Start

In order to launch a Linux process, QEMU needs the process executable itself and all the target (x86) dynamic libraries used by it.

- On x86, you can just try to launch any process by using the native libraries:

      qemu-i386 -L / /bin/ls

  `-L /` tells that the x86 dynamic linker must be searched with a ``/'` prefix.
- Since QEMU is also a linux process, you can launch qemu with qemu (NOTE: you can only do that if you compiled QEMU from the sources):

      qemu-i386 -L / qemu-i386 -L / /bin/ls

- On non x86 CPUs, you need first to download at least an x86 glibc (``qemu-runtime-i386-XXX-.tar.gz'` on the QEMU web page). Ensure that `LD_LIBRARY_PATH` is not set:

      unset LD_LIBRARY_PATH

  Then you can launch the precompiled ``ls'` x86 executable:

      qemu-i386 tests/i386/ls

  You can look at ``qemu-binfmt-conf.sh'` so that QEMU is automatically launched by the Linux kernel when you try to launch x86 executables. It requires the `binfmt_misc` module in the Linux kernel.
- The x86 version of QEMU is also included. You can try weird things such as:

      qemu-i386 /usr/local/qemu-i386/bin/qemu-i386 /usr/local/qemu-i386/bin/ls-i386

## 5.2 Wine launch

- Ensure that you have a working QEMU with the x86 glibc distribution (see previous section). In order to verify it, you must be able to do:

      qemu-i386 /usr/local/qemu-i386/bin/ls-i386

- Download the binary x86 Wine install (``qemu-XXX-i386-wine.tar.gz'` on the QEMU web page).
- Configure Wine on your account. Look at the provided script ``/usr/local/qemu-i386/bin/wine-conf.sh'`. Your previous `${HOME}/.wine` directory is saved to `${HOME}/.wine.org`.
- Then you can try the example ``putty.exe'`:

      qemu-i386 /usr/local/qemu-i386/wine/bin/wine /usr/local/qemu-i386/wine/c/Program\ Files/putty.exe

## 5.3 Command line options

    usage: qemu-i386 [-h] [-d] [-L path] [-s size] program [arguments...]

``-h'`
  Print the help
``-L path'`
  Set the x86 elf interpreter prefix (default=/usr/local/qemu-i386)
``-s size'`
  Set the x86 stack size in bytes (default=524288)

Debug options:

``-d'`
  Activate log (logfile=/tmp/qemu.log)
``-p pagesize'`
  Act as if the host page size was 'pagesize' bytes

# 6. Compilation from the sources

## 6.1 Linux/BSD

Read the ``README'` which gives the related information.

## 6.2 Windows

- Install the current versions of MSYS and MinGW from http://www.mingw.org/. You can find detailed installation instructions in the download section and the FAQ.
- Download the MinGW development library of SDL 1.2.x (``SDL-devel-1.2.x-mingw32.tar.gz'`) from http://www.libsdl.org. Unpack it in a temporary place, and unpack the archive ``i386-mingw32msvc.tar.gz'` in the MinGW tool directory. Edit the ``sdl-config'` script so that it gives the correct SDL directory when invoked.
- Extract the current version of QEMU.
- Start the MSYS shell (file ``msys.bat'`).
- Change to the QEMU directory. Launch ``./configure'` and ``make'`. If you have problems using SDL, verify that ``sdl-config'` can be launched from the MSYS command line.
- You can install QEMU in ``Program Files/Qemu'` by typing ``make install'`. Don't forget to copy ``SDL.dll'` in ``Program Files/Qemu'`.

## 6.3 Cross compilation for Windows with Linux

- Install the MinGW cross compilation tools available at http://www.mingw.org/.
- Install the Win32 version of SDL (http://www.libsdl.org) by unpacking ``i386-mingw32msvc.tar.gz'`. Set up the PATH environment variable so that ``i386-mingw32msvc-sdl-config'` can be launched by the QEMU configuration script.
- Configure QEMU for Windows cross compilation:

      ./configure --enable-mingw32

  If necessary, you can change the cross-prefix according to the prefix choosen for the MinGW tools with --cross-prefix. You can also use --prefix to set the Win32 install path.
- You can install QEMU in the installation directory by typing ``make install'`. Don't forget to copy ``SDL.dll'` in the installation directory.

Note: Currently, Wine does not seem able to launch QEMU for Win32.

## 6.4 Mac OS X

The Mac OS X patches are not fully merged in QEMU, so you should look at the QEMU mailing list archive to have all the necessary information.

This document was generated on 15 November 2004 using texi2html 1.56k.