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\input texinfo @c -*- texinfo -*-

@iftex

@settitle QEMU CPU Emulator User Documentation

@titlepage

@sp 7

@center @titlefont{QEMU CPU Emulator User Documentation}

@sp 3

@end titlepage

@end iftex

@chapter Introduction

@section Features

QEMU is a FAST! processor emulator using dynamic translation to

achieve good emulation speed.

QEMU has two operating modes:

@itemize @minus

@item 

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.

@item 

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 (@url{http://www.winehq.org}) or

to ease cross-compilation and cross-debugging.

@end itemize

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:

@itemize

@item PC (x86 processor)

@item PREP (PowerPC processor)

@item PowerMac (PowerPC processor, in progress)

@end itemize

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

@chapter Installation

If you want to compile QEMU yourself, see @ref{compilation}.

@section Linux

Download the binary distribution (@file{qemu-XXX-i386.tar.gz}) and

untar it as root in @file{/}:

@example

su

cd /

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

@end example

@section Windows

Download the experimental binary installer at

@url{http://www.freeoszoo.org/download.php}.

@section Mac OS X

Download the experimental binary installer at

@url{http://www.freeoszoo.org/download.php}.

@chapter QEMU PC System emulator invocation

@section Introduction

@c man begin DESCRIPTION

The QEMU System emulator simulates a complete PC.

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

available:

@enumerate

@item 

@code{qemu-fast} uses the host Memory Management Unit (MMU) to

simulate the x86 MMU. It is @emph{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 (@xref{linux_compile}) 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

@code{qemu-fast} code by writing at the right addresses).

@item 

@code{qemu} uses a software MMU. It is about @emph{two times slower}

but gives a more accurate emulation and a complete separation between

the host and target address spaces.

@end enumerate

QEMU emulates the following PC peripherials:

@itemize @minus

@item 

i440FX host PCI bridge and PIIX3 PCI to ISA bridge

@item

Cirrus CLGD 5446 PCI VGA card or dummy VGA card with Bochs VESA

extensions (hardware level, including all non standard modes).

@item

PS/2 mouse and keyboard

@item 

2 PCI IDE interfaces with hard disk and CD-ROM support

@item

Floppy disk

@item 

NE2000 PCI network adapters

@item

Serial ports

@item

Soundblaster 16 card

@end itemize

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

VGA BIOS.

@c man end

@section Quick Start

Download and uncompress the linux image (@file{linux.img}) and type:

@example

qemu linux.img

@end example

Linux should boot and give you a prompt.

@section Invocation

@example

@c man begin SYNOPSIS

usage: qemu [options] [disk_image]

@c man end

@end example

@c man begin OPTIONS

@var{disk_image} is a raw hard disk image for IDE hard disk 0.

General options:

@table @option

@item -fda file

@item -fdb file

Use @var{file} as floppy disk 0/1 image (@xref{disk_images}). You can

use the host floppy by using @file{/dev/fd0} as filename.

@item -hda file

@item -hdb file

@item -hdc file

@item -hdd file

Use @var{file} as hard disk 0, 1, 2 or 3 image (@xref{disk_images}).

@item -cdrom file

Use @var{file} as CD-ROM image (you cannot use @option{-hdc} and and

@option{-cdrom} at the same time). You can use the host CD-ROM by

using @file{/dev/cdrom} as filename.

@item -boot [a|c|d]

Boot on floppy (a), hard disk (c) or CD-ROM (d). Hard disk boot is

the default.

@item -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 @key{C-a s} (@xref{disk_images}). 

@item -m megs

Set virtual RAM size to @var{megs} megabytes. Default is 128 MB.

@item -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.

@item -enable-audio

The SB16 emulation is disabled by default as it may give problems with

Windows. You can enable it manually with this option.

@item -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.

@end table

Network options:

@table @option

@item -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.

@item -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.

@item -tun-fd fd

Assumes @var{fd} talks to a tap/tun host network interface and use

it. Read @url{http://bellard.org/qemu/tetrinet.html} to have an

example of its use.

@item -user-net 

Use the user mode network stack. This is the default if no tun/tap

network init script is found.

@item -tftp prefix

When using the user mode network stack, activate a built-in TFTP

server. All filenames beginning with @var{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 @code{bin} of

the Unix TFTP client). The host IP address on the guest is as usual

10.0.2.2.

@item -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 @var{host-port} to the guest

@var{guest-host} on guest port @var{guest-port}. If @var{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:

@example

# on the host

qemu -redir tcp:6001::6000 [...]

# this host xterm should open in the guest X11 server

xterm -display :1

@end example

To redirect telnet connections from host port 5555 to telnet port on

the guest, use the following:

@example

# on the host

qemu -redir tcp:5555::23 [...]

telnet localhost 5555

@end example

Then when you use on the host @code{telnet localhost 5555}, you

connect to the guest telnet server.

@item -dummy-net 

Use the dummy network stack: no packet will be received by the network

cards.

@end table

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.

@table @option

@item -kernel bzImage 

Use @var{bzImage} as kernel image.

@item -append cmdline 

Use @var{cmdline} as kernel command line

@item -initrd file

Use @var{file} as initial ram disk.

@end table

Debug/Expert options:

@table @option

@item -serial dev

Redirect the virtual serial port to host device @var{dev}. Available

devices are:

@table @code

@item vc

Virtual console

@item pty

[Linux only] Pseudo TTY (a new PTY is automatically allocated)

@item null

void device

@item stdio

[Unix only] standard input/output

@end table

The default device is @code{vc} in graphical mode and @code{stdio} in

non graphical mode.

This option can be used several times to simulate up to 4 serials

ports.

@item -monitor dev

Redirect the monitor to host device @var{dev} (same devices as the

serial port).

The default device is @code{vc} in graphical mode and @code{stdio} in

non graphical mode.

@item -s

Wait gdb connection to port 1234 (@xref{gdb_usage}). 

@item -p port

Change gdb connection port.

@item -S

Do not start CPU at startup (you must type 'c' in the monitor).

@item -d             

Output log in /tmp/qemu.log

@item -isa

Simulate an ISA-only system (default is PCI system).

@item -std-vga

Simulate a standard VGA card with Bochs VBE extensions (default is

Cirrus Logic GD5446 PCI VGA)

@end table

@c man end

@section Keys

@c man begin OPTIONS

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

@table @key

@item Ctrl-Shift-f

Toggle full screen

@item Ctrl-Shift-Fn

Switch to virtual console 'n'. Standard console mappings are:

@table @emph

@item 1

Target system display

@item 2

Monitor

@item 3

Serial port

@end table

@item Ctrl-Shift

Toggle mouse and keyboard grab.

@end table

In the virtual consoles, you can use @key{Ctrl-Up}, @key{Ctrl-Down},

@key{Ctrl-PageUp} and @key{Ctrl-PageDown} to move in the back log.

During emulation, if you are using the @option{-nographic} option, use

@key{Ctrl-a h} to get terminal commands:

@table @key

@item Ctrl-a h

Print this help

@item Ctrl-a x    

Exit emulatior

@item Ctrl-a s    

Save disk data back to file (if -snapshot)

@item Ctrl-a b

Send break (magic sysrq in Linux)

@item Ctrl-a c

Switch between console and monitor

@item Ctrl-a Ctrl-a

Send Ctrl-a

@end table

@c man end

@ignore

@setfilename qemu 

@settitle QEMU System Emulator

@c man begin SEEALSO

The HTML documentation of QEMU for more precise information and Linux

user mode emulator invocation.

@c man end

@c man begin AUTHOR

Fabrice Bellard

@c man end

@end ignore

@end ignore

@section QEMU Monitor

The QEMU monitor is used to give complex commands to the QEMU

emulator. You can use it to:

@itemize @minus

@item

Remove or insert removable medias images

(such as CD-ROM or floppies)

@item 

Freeze/unfreeze the Virtual Machine (VM) and save or restore its state

from a disk file.

@item Inspect the VM state without an external debugger.

@end itemize

@subsection Commands

The following commands are available:

@table @option

@item help or ? [cmd]

Show the help for all commands or just for command @var{cmd}.

@item commit  

Commit changes to the disk images (if -snapshot is used)

@item info subcommand 

show various information about the system state

@table @option

@item info network

show the network state

@item info block

show the block devices

@item info registers

show the cpu registers

@item info history

show the command line history

@end table

@item q or quit

Quit the emulator.

@item eject [-f] device

Eject a removable media (use -f to force it).

@item change device filename

Change a removable media.

@item screendump filename

Save screen into PPM image @var{filename}.

@item log item1[,...]

Activate logging of the specified items to @file{/tmp/qemu.log}.

@item savevm filename

Save the whole virtual machine state to @var{filename}.

@item loadvm filename

Restore the whole virtual machine state from @var{filename}.

@item stop

Stop emulation.

@item c or cont

Resume emulation.

@item gdbserver [port]

Start gdbserver session (default port=1234)

@item x/fmt addr

Virtual memory dump starting at @var{addr}.

@item xp /fmt addr

Physical memory dump starting at @var{addr}.

@var{fmt} is a format which tells the command how to format the

data. Its syntax is: @option{/@{count@}@{format@}@{size@}}

@table @var

@item count 

is the number of items to be dumped.

@item format

can be x (hexa), d (signed decimal), u (unsigned decimal), o (octal),

c (char) or i (asm instruction).

@item size

can be b (8 bits), h (16 bits), w (32 bits) or g (64 bits). On x86,

@code{h} or @code{w} can be specified with the @code{i} format to

respectively select 16 or 32 bit code instruction size.

@end table

Examples: 

@itemize

@item

Dump 10 instructions at the current instruction pointer:

@example 

(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

@end example

@item

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

@example 

(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

@end example

@end itemize

@item p or print/fmt expr

Print expression value. Only the @var{format} part of @var{fmt} is

used.

@item sendkey keys

Send @var{keys} to the emulator. Use @code{-} to press several keys

simultaneously. Example:

@example

sendkey ctrl-alt-f1

@end example

This command is useful to send keys that your graphical user interface

intercepts at low level, such as @code{ctrl-alt-f1} in X Window.

@item system_reset

Reset the system.

@end table

@subsection 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 @emph{$}.

@node disk_images

@section Disk Images

@subsection Raw disk images

The disk images can simply be raw images of the hard disk. You can

create them with the command:

@example

dd of=myimage bs=1024 seek=mysize count=0

@end example

where @var{myimage} is the image filename and @var{mysize} is its size

in kilobytes.

@subsection Snapshot mode

If you use the option @option{-snapshot}, all disk images are

considered as read only. When sectors in written, they are written in

a temporary file created in @file{/tmp}. You can however force the

write back to the raw disk images by pressing @key{C-a s}.

NOTE: The snapshot mode only works with raw disk images.

@subsection Copy On Write disk images

QEMU also supports user mode Linux

(@url{http://user-mode-linux.sourceforge.net/}) Copy On Write (COW)

disk images. The COW disk images are much smaller than normal images

as they store only modified sectors. They also permit the use of the

same disk image template for many users.

To create a COW disk images, use the command:

@example

qemu-mkcow -f myrawimage.bin mycowimage.cow

@end example

@file{myrawimage.bin} is a raw image you want to use as original disk

image. It will never be written to.

@file{mycowimage.cow} is the COW disk image which is created by

@code{qemu-mkcow}. You can use it directly with the @option{-hdx}

options. You must not modify the original raw disk image if you use

COW images, as COW images only store the modified sectors from the raw

disk image. QEMU stores the original raw disk image name and its

modified time in the COW disk image so that chances of mistakes are

reduced.

If the raw disk image is not read-only, by pressing @key{C-a s} you

can flush the COW disk image back into the raw disk image, as in

snapshot mode.

COW disk images can also be created without a corresponding raw disk

image. It is useful to have a big initial virtual disk image without

using much disk space. Use:

@example

qemu-mkcow mycowimage.cow 1024

@end example

to create a 1 gigabyte empty COW disk image.

NOTES: 

@enumerate

@item

COW disk images must be created on file systems supporting

@emph{holes} such as ext2 or ext3.

@item 

Since holes are used, the displayed size of the COW disk image is not

the real one. To know it, use the @code{ls -ls} command.

@end enumerate

@subsection Convert VMware disk images to raw disk images

You can use the tool @file{vmdk2raw} to convert VMware disk images to

raw disk images directly usable by QEMU. The syntax is:

@example

vmdk2raw vmware_image output_image

@end example

@section Network emulation

QEMU simulates up to 6 networks cards (NE2000 boards). Each card can

be connected to a specific host network interface.

@subsection Using tun/tap network interface

This is the standard way to emulate network. QEMU adds a virtual

network device on your host (called @code{tun0}), and you can then

configure it as if it was a real ethernet card.

As an example, you can download the @file{linux-test-xxx.tar.gz}

archive and copy the script @file{qemu-ifup} in @file{/etc} and

configure properly @code{sudo} so that the command @code{ifconfig}

contained in @file{qemu-ifup} can be executed as root. You must verify

that your host kernel supports the TUN/TAP network interfaces: the

device @file{/dev/net/tun} must be present.

See @ref{direct_linux_boot} to have an example of network use with a

Linux distribution.

@subsection Using the user mode network stack

By using the option @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:

@example

QEMU Virtual Machine    <------>  Firewall/DHCP server <-----> Internet

     (10.0.2.x)            |          (10.0.2.2)

                           |

                           ---->  DNS 

                              (10.0.2.3)

@end example

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 @code{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 @option{-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.

@node direct_linux_boot

@section 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.

@enumerate

@item

Download the archive @file{linux-test-xxx.tar.gz} containing a Linux

kernel and a disk image. 

@item Optional: If you want network support (for example to launch X11 examples), you

must copy the script @file{qemu-ifup} in @file{/etc} and configure

properly @code{sudo} so that the command @code{ifconfig} contained in

@file{qemu-ifup} can be executed as root. You must verify that your host

kernel supports the TUN/TAP network interfaces: the device

@file{/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.

@item Launch @code{qemu.sh}. You should have the following output:

@example

> ./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# 

@end example

@item

Then you can play with the kernel inside the virtual serial console. You

can launch @code{ls} for example. Type @key{Ctrl-a h} to have an help

about the keys you can type inside the virtual serial console. In

particular, use @key{Ctrl-a x} to exit QEMU and use @key{Ctrl-a b} as

the Magic SysRq key.

@item 

If the network is enabled, launch the script @file{/etc/linuxrc} in the

emulator (don't forget the leading dot):

@example

. /etc/linuxrc

@end example

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

@example

xhost +172.20.0.2

@end example

You can now launch @file{xterm} or @file{xlogo} and verify that you have

a real Virtual Linux system !

@end enumerate

NOTES:

@enumerate

@item 

A 2.5.74 kernel is also included in the archive. Just

replace the bzImage in qemu.sh to try it.

@item 

qemu-fast creates a temporary file in @var{$QEMU_TMPDIR} (@file{/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.

@item 

In order to exit cleanly from qemu, you can do a @emph{shutdown} inside

qemu. qemu will automatically exit when the Linux shutdown is done.

@item 

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:

@example

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

@end example

@item 

The example disk image is a modified version of the one made by Kevin

Lawton for the plex86 Project (@url{www.plex86.org}).

@end enumerate

@node linux_compile

@section Linux Kernel Compilation

You can use any linux kernel with QEMU. However, if you want to use

@code{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 @file{linux-2.6-qemu-fast.patch} made by Rusty

Russel available in the QEMU source archive. Otherwise, you can make the

following changes @emph{by hand} to the Linux kernel:

@enumerate

@item

The kernel must be mapped at 0x90000000 (the default is

0xc0000000). You must modify only two lines in the kernel source:

In @file{include/asm/page.h}, replace

@example

#define __PAGE_OFFSET           (0xc0000000)

@end example

by

@example

#define __PAGE_OFFSET           (0x90000000)

@end example

And in @file{arch/i386/vmlinux.lds}, replace

@example

  . = 0xc0000000 + 0x100000;

@end example

by 

@example

  . = 0x90000000 + 0x100000;

@end example

@item

If you want to enable SMP (Symmetric Multi-Processing) support, you

must make the following change in @file{include/asm/fixmap.h}. Replace

@example

#define FIXADDR_TOP	(0xffffX000UL)

@end example

by 

@example

#define FIXADDR_TOP	(0xa7ffX000UL)

@end example

(X is 'e' or 'f' depending on the kernel version). Although you can

use an SMP kernel with QEMU, it only supports one CPU.

@item

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

@file{include/asm/param.h}, replace:

@example

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

@end example

by

@example

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

@end example

@end enumerate

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

Just type

@example

make bzImage

@end example

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

@file{arch/i386/boot/bzImage}).

@node gdb_usage

@section 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:

@example

> 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

@end example

Then launch gdb on the 'vmlinux' executable:

@example

> gdb vmlinux

@end example

In gdb, connect to QEMU:

@example

(gdb) target remote localhost:1234

@end example

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

@example

(gdb) c

@end example

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

@enumerate

@item

Use @code{info reg} to display all the CPU registers.

@item

Use @code{x/10i $eip} to display the code at the PC position.

@item

Use @code{set architecture i8086} to dump 16 bit code. Then use

@code{x/10i $cs*16+*eip} to dump the code at the PC position.

@end enumerate

@section Target OS specific information

@subsection Linux

To have access to SVGA graphic modes under X11, use the @code{vesa} or

the @code{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

@code{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.

@subsection 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.

@subsubsection 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.

@subsubsection CPU usage reduction

Windows 9x does not correctly use the CPU HLT