qemu-doc.texi

\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 peripherals. 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

QEMU can run without an host kernel driver and yet gives acceptable
performance. 

For system emulation, the following hardware targets are supported:
@itemize
@item PC (x86 processor)
@item PREP (PowerPC processor)
@item PowerMac (PowerPC processor, in progress)
@item Sun4m (32-bit Sparc processor)
@item Sun4u (64-bit Sparc processor, in progress)
@end itemize

For user emulation, x86, PowerPC, ARM, and Sparc32/64 CPUs are supported.

@chapter Installation

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

@section Linux

If a precompiled package is available for your distribution - you just
have to install it. Otherwise, see @ref{compilation}.

@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 the
following PC peripherals:

@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 -k language

Use keyboard layout @var{language} (for example @code{fr} for
French). This option is only needed where it is not easy to get raw PC
keycodes (e.g. on Macs or with some X11 servers). You don't need to
use it on PC/Linux or PC/Windows hosts.

The available layouts are:
@example
ar  de-ch  es  fo     fr-ca  hu  ja  mk     no  pt-br  sv
da  en-gb  et  fr     fr-ch  is  lt  nl     pl  ru     th
de  en-us  fi  fr-be  hr     it  lv  nl-be  pt  sl     tr
@end example

The default is @code{en-us}.

@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.

@item -full-screen
Start in full screen.

@item -pidfile file
Store the QEMU process PID in @var{file}. It is useful if you launch QEMU
from a script.

@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 -nics n

Simulate @var{n} network cards (the default is 1).

@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 -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 @file{dir}
transparently.

In the guest Windows OS, the line:
@example
10.0.2.4 smbserver
@end example
must be added in the file @file{C:\WINDOWS\LMHOSTS} (for windows 9x/Me)
or @file{C:\WINNT\SYSTEM32\DRIVERS\ETC\LMHOSTS} (Windows NT/2000).

Then @file{dir} can be accessed in @file{\\smbserver\qemu}.

Note that a SAMBA server must be installed on the host OS in
@file{/usr/sbin/smbd}. QEMU was tested succesfully with smbd version
2.2.7a from the Red Hat 9.

@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 -hdachs c,h,s,[,t]
Force hard disk 0 physical geometry (1 <= @var{c} <= 16383, 1 <=
@var{h} <= 16, 1 <= @var{s} <= 63) and optionally force the BIOS
translation mode (@var{t}=none, lba or auto). Usually QEMU can guess
all thoses parameters. This option is useful for old MS-DOS disk
images.

@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)
@item -loadvm file
Start right away with a saved state (@code{loadvm} in monitor)
@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-Alt-f
Toggle full screen

@item Ctrl-Alt-n
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-Alt
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

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.

@subsection Quick start for disk image creation

You can create a disk image with the command:
@example
qemu-img create myimage.img mysize
@end example
where @var{myimage.img} is the disk image filename and @var{mysize} is its
size in kilobytes. You can add an @code{M} suffix to give the size in
megabytes and a @code{G} suffix for gigabytes.

@xref{qemu_img_invocation} for more information.

@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 using the @code{commit} monitor
command (or @key{C-a s} in the serial console).

@node qemu_img_invocation
@subsection @code{qemu-img} Invocation

@include qemu-img.texi

@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 server (10.0.2.3)
                           |     
                           ---->  SMB server (10.0.2.4)
@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 
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 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.

When using a 2.6 guest Linux kernel, verify that the 4G/4G patch is
not activated because QEMU is slower with this patch. The QEMU
Accelerator Module is also much slower in this case. Earlier Fedora
Core 3 Linux kernel (< 2.6.9-1.724_FC3) were known to incorporte this
patch by default. Newer kernels don't have it.

@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
instruction. The result is that it takes host CPU cycles even when
idle. You can install the utility from
@url{http://www.user.cityline.ru/~maxamn/amnhltm.zip} to solve this
problem. Note that no such tool is needed for NT, 2000 or XP.

@subsubsection Windows 2000 disk full problems

Currently (release 0.6.0) QEMU has a bug which gives a @code{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 @code{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.

@subsubsection Windows XP security problems

Some releases of Windows XP install correctly but give a security
error when booting:
@example
A problem is preventing Windows from accurately checking the
license for this computer. Error code: 0x800703e6.
@end example
The only known workaround is to boot in Safe mode
without networking support. 

Future QEMU releases are likely to correct this bug.

@subsection MS-DOS and FreeDOS

@subsubsection 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 @url{http://www.vmware.com/software/dosidle210.zip} to solve this
problem.

@chapter QEMU PowerPC System emulator invocation

Use the executable @file{qemu-system-ppc} to simulate a complete PREP
or PowerMac PowerPC system.

QEMU emulates the following PowerMac peripherals:

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

QEMU emulates the following PREP peripherals:

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

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

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

@c man begin OPTIONS

The following options are specific to the PowerPC emulation:

@table @option

@item -prep
Simulate a PREP system (default is PowerMAC)

@item -g WxH[xDEPTH]  

Set the initial VGA graphic mode. The default is 800x600x15.

@end table

@c man end 


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

@chapter Sparc32 System emulator invocation

Use the executable @file{qemu-system-sparc} to simulate a JavaStation
(sun4m architecture). The emulation is somewhat complete.

QEMU emulates the following sun4m peripherals:

@itemize @minus
@item
IOMMU
@item
TCX Frame buffer
@item 
Lance (Am7990) Ethernet
@item
Non Volatile RAM M48T08
@item
Slave I/O: timers, interrupt controllers, Zilog serial ports, keyboard
and power/reset logic
@item
ESP SCSI controller with hard disk and CD-ROM support
@item
Floppy drive
@end itemize

The number of peripherals is fixed in the architecture.

QEMU uses the Proll, a PROM replacement available at
@url{http://people.redhat.com/zaitcev/linux/}. The required
QEMU-specific patches are included with the sources.

A sample Linux 2.6 series kernel and ram disk image are available on
the QEMU web site. Please note that currently neither Linux 2.4
series, NetBSD, nor OpenBSD kernels work.

@c man begin OPTIONS

The following options are specific to the Sparc emulation:

@table @option

@item -g WxH

Set the initial TCX graphic mode. The default is 1024x768.

@end table

@c man end 

@chapter Sparc64 System emulator invocation

Use the executable @file{qemu-system-sparc64} to simulate a Sun4u machine.
The emulator is not usable for anything yet.

@chapter QEMU User space emulator invocation

@section 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. 

@itemize

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

@example 
qemu-i386 -L / /bin/ls
@end example

@code{-L /} tells that the x86 dynamic linker must be searched with a
@file{/} prefix.

@item 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):

@example 
qemu-i386 -L / qemu-i386 -L / /bin/ls
@end example

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

@example
unset LD_LIBRARY_PATH 
@end example

Then you can launch the precompiled @file{ls} x86 executable:

@example
qemu-i386 tests/i386/ls
@end example
You can look at @file{qemu-binfmt-conf.sh} so that
QEMU is automatically launched by the Linux kernel when you try to
launch x86 executables. It requires the @code{binfmt_misc} module in the
Linux kernel.

@item The x86 version of QEMU is also included. You can try weird things such as:
@example
qemu-i386 /usr/local/qemu-i386/bin/qemu-i386 /usr/local/qemu-i386/bin/ls-i386
@end example

@end itemize

@section Wine launch

@itemize

@item 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:

@example
qemu-i386 /usr/local/qemu-i386/bin/ls-i386
@end example

@item Download the binary x86 Wine install
(@file{qemu-XXX-i386-wine.tar.gz} on the QEMU web page). 

@item Configure Wine on your account. Look at the provided script
@file{/usr/local/qemu-i386/bin/wine-conf.sh}. Your previous
@code{$@{HOME@}/.wine} directory is saved to @code{$@{HOME@}/.wine.org}.

@item Then you can try the example @file{putty.exe}:

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

@end itemize

@section Command line options

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

@table @option
@item -h
Print the help
@item -L path   
Set the x86 elf interpreter prefix (default=/usr/local/qemu-i386)
@item -s size
Set the x86 stack size in bytes (default=524288)
@end table

Debug options:

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

@node compilation
@chapter Compilation from the sources

@section Linux/Unix

@subsection Compilation

First you must decompress the sources:
@example
cd /tmp
tar zxvf qemu-x.y.z.tar.gz
cd qemu-x.y.z
@end example

Then you configure QEMU and build it (usually no options are needed):
@example
./configure
make
@end example

Then type as root user:
@example
make install
@end example
to install QEMU in @file{/usr/local}.

@subsection Tested tool versions

In order to compile QEMU succesfully, it is very important that you
have the right tools. The most important one is gcc. I cannot guaranty
that QEMU works if you do not use a tested gcc version. Look at
'configure' and 'Makefile' if you want to make a different gcc
version work.

@example
host      gcc      binutils      glibc    linux       distribution
----------------------------------------------------------------------
x86       3.2      2.13.2        2.1.3    2.4.18
          2.96     2.11.93.0.2   2.2.5    2.4.18      Red Hat 7.3
          3.2.2    2.13.90.0.18  2.3.2    2.4.20      Red Hat 9

PowerPC   3.3 [4]  2.13.90.0.18  2.3.1    2.4.20briq
          3.2

Alpha     3.3 [1]  2.14.90.0.4   2.2.5    2.2.20 [2]  Debian 3.0

Sparc32   2.95.4   2.12.90.0.1   2.2.5    2.4.18      Debian 3.0

ARM       2.95.4   2.12.90.0.1   2.2.5    2.4.9 [3]   Debian 3.0

[1] On Alpha, QEMU needs the gcc 'visibility' attribute only available
    for gcc version >= 3.3.
[2] Linux >= 2.4.20 is necessary for precise exception support
    (untested).
[3] 2.4.9-ac10-rmk2-np1-cerf2

[4] gcc 2.95.x generates invalid code when using too many register
variables. You must use gcc 3.x on PowerPC.
@end example

@section Windows

@itemize
@item Install the current versions of MSYS and MinGW from
@url{http://www.mingw.org/}. You can find detailed installation
instructions in the download section and the FAQ.

@item Download 
the MinGW development library of SDL 1.2.x
(@file{SDL-devel-1.2.x-mingw32.tar.gz}) from
@url{http://www.libsdl.org}. Unpack it in a temporary place, and
unpack the archive @file{i386-mingw32msvc.tar.gz} in the MinGW tool
directory. Edit the @file{sdl-config} script so that it gives the
correct SDL directory when invoked.

@item Extract the current version of QEMU.
 
@item Start the MSYS shell (file @file{msys.bat}).

@item Change to the QEMU directory. Launch @file{./configure} and 
@file{make}.  If you have problems using SDL, verify that
@file{sdl-config} can be launched from the MSYS command line.

@item You can install QEMU in @file{Program Files/Qemu} by typing 
@file{make install}. Don't forget to copy @file{SDL.dll} in
@file{Program Files/Qemu}.

@end itemize

@section Cross compilation for Windows with Linux

@itemize
@item
Install the MinGW cross compilation tools available at
@url{http://www.mingw.org/}.

@item 
Install the Win32 version of SDL (@url{http://www.libsdl.org}) by
unpacking @file{i386-mingw32msvc.tar.gz}. Set up the PATH environment
variable so that @file{i386-mingw32msvc-sdl-config} can be launched by
the QEMU configuration script.

@item 
Configure QEMU for Windows cross compilation:
@example
./configure --enable-mingw32
@end example
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.

@item You can install QEMU in the installation directory by typing 
@file{make install}. Don't forget to copy @file{SDL.dll} in the
installation directory. 

@end itemize

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

@section 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.