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 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)
@end itemize

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

@chapter Installation

@section Linux

If you want to compile QEMU, please read the @file{README} which gives
the related information. Otherwise just 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

@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

Mac OS X is currently not supported.

@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 Linux kernel
must be used (@xref{linux_compile}).

@item 
@code{qemu} uses a software MMU. It is about @emph{two times 
slower} but gives a more accurate emulation. 

@end enumerate

QEMU emulates the following PC peripherials:

@itemize @minus
@item
VGA (hardware level, including all non standard modes)
@item
PS/2 mouse and keyboard
@item 
2 IDE interfaces with hard disk and CD-ROM support
@item
Floppy disk
@item 
up to 6 NE2000 network adapters
@item
Serial port
@item 
Soundblaster 16 card
@end itemize

@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.

@item -initrd file
Use @var{file} as initial ram disk.

@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.

@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 
(Experimental) Use the user mode network stack. This is the default if
no tun/tap network init script is found.

@item -dummy-net 
Use the dummy network stack: no packet will be received on 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 options:
@table @option
@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
@end table

During the graphical emulation, you can use the following keys:
@table @key
@item Ctrl-Shift
Toggle mouse and keyboard grab.
@item Ctrl-Shift-f
Toggle full screen
@end table

During emulation, if you are using the serial console, use @key{C-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.

@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

@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

This is @emph{experimental} (version 0.5.4). You must configure qemu
with @code{--enable-slirp}. Then 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).

@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}
X11 driver. For optimal performances, use the same depth as your
native display.

@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.

SVGA graphic modes support: QEMU currently supports the Bochs VESA VBE
extensions. It supports color depths of 8, 15, 16 and 32 bits per
pixel in 640x480, 800x600 and 1024x768. For optimal performances, use
the same depth as your native display.

@itemize

@item Windows XP: it should be automatically detected.

@item Windows NT4 or 2000: use the driver
@url{http://www.volny.cz/xnavara/qemuvid_bin.zip} by Filip Navara.

@item Windows 95/98/Me: no clean solution yet (but it will change
soon). You can however use the shareware driver from SciTech. Here are
the steps recommended by Christophe Bothamy on the Bochs mailing list:

@itemize
@item install win95 with the VGA driver.
@item download sdd 7 beta from @url{http://www.majorgeeks.com/download382.html}
@item download pmhelp.vxd from @url{http://unununium.org/viewcvs/snap/redist/release/pmhelp.vxd}
@item copy pmhelp.vxd to the win95 system directory
@item install sdd7
@end itemize
@end itemize

@chapter QEMU PREP PowerPC System emulator invocation

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

QEMU emulates the following PREP peripherials:

@itemize @minus
@item 
2 IDE interfaces with hard disk and CD-ROM support
@item
Floppy disk
@item 
up to 6 NE2000 network adapters
@item
Serial port
@item
PREP Non Volatile RAM
@end itemize

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

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

@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