\input texinfo @c -*- texinfo -*-
-@settitle QEMU x86 Emulator Reference Documentation
+@settitle QEMU CPU Emulator Reference Documentation
@titlepage
@sp 7
-@center @titlefont{QEMU x86 Emulator Reference Documentation}
+@center @titlefont{QEMU CPU Emulator Reference Documentation}
@sp 3
@end titlepage
@chapter Introduction
-QEMU is an x86 processor emulator. Its purpose is to run x86 Linux
-processes on non-x86 Linux architectures such as PowerPC. By using
-dynamic translation it achieves a reasonnable speed while being easy to
-port on new host CPUs. Its main goal is to be able to launch the
-@code{Wine} Windows API emulator (@url{http://www.winehq.org}) or
-@code{DOSEMU} (@url{http://www.dosemu.org}) on non-x86 CPUs.
+@section Features
-QEMU features:
+QEMU is a FAST! processor emulator. By using dynamic translation it
+achieves a reasonnable speed while being easy to port on new host
+CPUs.
-@itemize
+QEMU has two operating modes:
+@itemize
+@item User mode emulation. In this mode, QEMU can launch Linux processes
+compiled for one CPU on another CPU. Linux system calls are converted
+because of endianness and 32/64 bit mismatches. The Wine Windows API
+emulator (@url{http://www.winehq.org}) and the DOSEMU DOS emulator
+(@url{www.dosemu.org}) are the main targets for QEMU.
+
+@item Full system emulation. In this mode, QEMU emulates a full
+system, including a processor and various peripherials. Currently, it
+is only used to launch an x86 Linux kernel on an x86 Linux system. It
+enables easier testing and debugging of system code. It can also be
+used to provide virtual hosting of several virtual PCs on a single
+server.
+
+@end itemize
+
+As QEMU requires no host kernel patches to run, it is very safe and
+easy to use.
-@item User space only x86 emulator.
+QEMU generic features:
-@item Currently ported on i386, PowerPC. Work in progress for S390, Alpha and Sparc.
+@itemize
+
+@item User space only or full system emulation.
@item Using dynamic translation to native code for reasonnable speed.
-@item The virtual x86 CPU supports 16 bit and 32 bit addressing with segmentation.
-User space LDT and GDT are emulated. VM86 mode is also supported.
+@item Working on x86 and PowerPC hosts. Being tested on ARM, Sparc32, Alpha and S390.
+
+@item Self-modifying code support.
+
+@item Precise exceptions support.
+@item The virtual CPU is a library (@code{libqemu}) which can be used
+in other projects.
+
+@end itemize
+
+QEMU user mode emulation features:
+@itemize
@item Generic Linux system call converter, including most ioctls.
@item clone() emulation using native CPU clone() to use Linux scheduler for threads.
-@item Accurate signal handling by remapping host signals to virtual x86 signals.
+@item Accurate signal handling by remapping host signals to target signals.
+@end itemize
+@end itemize
-@item Precise user space x86 exceptions.
+QEMU full system emulation features:
+@itemize
+@item Using mmap() system calls to simulate the MMU
+@end itemize
-@item Self-modifying code support.
+@section x86 emulation
-@item Support of host page sizes bigger than 4KB.
+QEMU x86 target features:
-@item QEMU can emulate itself on x86.
+@itemize
-@item The virtual x86 CPU is a library (@code{libqemu}) which can be used
-in other projects.
+@item The virtual x86 CPU supports 16 bit and 32 bit addressing with segmentation.
+LDT/GDT and IDT are emulated. VM86 mode is also supported to run DOSEMU.
+
+@item Support of host page sizes bigger than 4KB in user mode emulation.
+
+@item QEMU can emulate itself on x86.
@item An extensive Linux x86 CPU test program is included @file{tests/test-i386}.
It can be used to test other x86 virtual CPUs.
@item IPC syscalls are missing.
@item The x86 segment limits and access rights are not tested at every
-memory access (and will never be to have good performances).
+memory access.
@item On non x86 host CPUs, @code{double}s are used instead of the non standard
10 byte @code{long double}s of x86 for floating point emulation to get
maximum performances.
+@item Full system emulation only works if no data are mapped above the virtual address
+0xc0000000 (yet).
+
+@item Some priviledged instructions or behaviors are missing. Only the ones
+needed for proper Linux kernel operation are emulated.
+
+@item No memory separation between the kernel and the user processes is done.
+It will be implemented very soon.
+
@end itemize
-@chapter Invocation
+@section ARM emulation
+
+@itemize
+
+@item ARM emulation can currently launch small programs while using the
+generic dynamic code generation architecture of QEMU.
+
+@item No FPU support (yet).
+
+@item No automatic regression testing (yet).
+
+@end itemize
+
+@chapter QEMU User space emulator invocation
@section Quick Start
+If you need to compile QEMU, please read the @file{README} which gives
+the related information.
+
In order to launch a Linux process, QEMU needs the process executable
itself and all the target (x86) dynamic libraries used by it.
Act as if the host page size was 'pagesize' bytes
@end table
+@chapter QEMU System emulator invocation
+
+@section Quick Start
+
+This section explains how to launch a Linux kernel inside QEMU.
+
+@enumerate
+@item
+Download the archive @file{vl-test-xxx.tar.gz} containing a Linux
+kernel and a disk image. The archive also contains a precompiled
+version of @file{vl}, the QEMU System emulator.
+
+@item Optional: If you want network support (for example to launch X11 examples), you
+must copy the script @file{vl-ifup} in @file{/etc} and configure
+properly @code{sudo} so that the command @code{ifconfig} contained in
+@file{vl-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{vl.sh}. You should have the following output:
+
+@example
+> ./vl.sh
+connected to host network interface: tun0
+Uncompressing Linux... Ok, booting the kernel.
+Linux version 2.4.20 (fabrice@localhost.localdomain) (gcc version 2.96 20000731 (Red Hat Linux 7.3 2.96-110)) #22 lun jui 7 13:37:41 CEST 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 ide1=noprobe ide2=noprobe ide3=noprobe ide4=noprobe ide5=noprobe
+ide_setup: ide1=noprobe
+ide_setup: ide2=noprobe
+ide_setup: ide3=noprobe
+ide_setup: ide4=noprobe
+ide_setup: ide5=noprobe
+Initializing CPU#0
+Detected 501.285 MHz processor.
+Calibrating delay loop... 989.59 BogoMIPS
+Memory: 29268k/32768k available (907k kernel code, 3112k reserved, 212k data, 52k 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
+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
+Uniform Multi-Platform E-IDE driver Revision: 6.31
+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: 12288 sectors (6 MB) w/256KiB Cache, CHS=12/16/63
+Partition check:
+ hda: unknown partition table
+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
+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: 52k freed
+sh: can't access tty; job control turned off
+#
+@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 vl-test archive. Just
+replace the bzImage in vl.sh to try it.
+
+@item
+vl creates a temporary file in @var{$VLTMPDIR} (@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 for vl, you can do a @emph{shutdown} inside
+vl. vl 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
+
+@section Invocation
+
+@example
+usage: vl [options] bzImage [kernel parameters...]
+@end example
+
+@file{bzImage} is a Linux kernel image.
+
+General options:
+@table @option
+@item -hda file
+@item -hdb file
+Use 'file' as hard disk 0 or 1 image (@xref{disk_images}).
+
+@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 -n script
+Set network init script [default=/etc/vl-ifup]. This script is
+launched to configure the host network interface (usually tun0)
+corresponding to the virtual NE2000 card.
+
+@item -initrd file
+Use 'file' as initial ram disk.
+@end table
+
+Debug options:
+@table @option
+@item -s
+Wait gdb connection to port 1234.
+@item -p port
+Change gdb connection port.
+@item -d
+Output log in /tmp/vl.log
+@end table
+
+During emulation, use @key{C-a h} to get terminal commands:
+
+@table @key
+@item C-a h
+Print this help
+@item C-a x
+Exit emulatior
+@item C-a s
+Save disk data back to file (if -snapshot)
+@item C-a b
+Send break (magic sysrq)
+@item C-a C-a
+Send C-a
+@end table
+
+@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 if=/dev/zero of=myimage bs=1024 count=mysize
+@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
+vlmkcow -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{vlmkcow}. 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
+vlmkcow 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 Linux Kernel Compilation
+
+You should be able to use any kernel with QEMU provided you make the
+following changes (only 2.4.x and 2.5.x were tested):
+
+@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 2.5 kernel as host kernel but if you use a target
+2.5 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 < 2.5. 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}).
+
+@section PC Emulation
+
+QEMU emulates the following PC peripherials:
+
+@itemize
+@item
+PIC (interrupt controler)
+@item
+PIT (timers)
+@item
+CMOS memory
+@item
+Dumb VGA (to print the @code{Uncompressing Linux} message)
+@item
+Serial port (port=0x3f8, irq=4)
+@item
+NE2000 network adapter (port=0x300, irq=9)
+@item
+IDE disk interface (port=0x1f0, irq=14)
+@end itemize
+
+@section GDB usage
+
+QEMU has a primitive support to work with gdb, so that you can do
+'Ctrl-C' while the kernel is running and inspect its state.
+
+In order to use gdb, launch vl with the '-s' option. It will wait for a
+gdb connection:
+@example
+> vl -s arch/i386/boot/bzImage -hda root-2.4.20.img 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 locahost:1234
+@end example
+
+Then you can use gdb normally. For example, type 'c' to launch the kernel:
+@example
+(gdb) c
+@end example
+
+WARNING: breakpoints and single stepping are not yet supported.
+
@chapter QEMU Internals
@section QEMU compared to other emulators
-Unlike bochs [3], QEMU emulates only a user space x86 CPU. It means that
-you cannot launch an operating system with it. The benefit is that it is
-simpler and faster due to the fact that some of the low level CPU state
-can be ignored (in particular, no virtual memory needs to be emulated).
+Like bochs [3], QEMU emulates an x86 CPU. But QEMU is much faster than
+bochs as it uses dynamic compilation and because it uses the host MMU to
+simulate the x86 MMU. The downside is that currently the emulation is
+not as accurate as bochs (for example, you cannot currently run Windows
+inside QEMU).
Like Valgrind [2], QEMU does user space emulation and dynamic
translation. Valgrind is mainly a memory debugger while QEMU has no
-support for it (QEMU could be used to detect out of bound memory accesses
-as Valgrind, but it has no support to track uninitialised data as
-Valgrind does). Valgrind dynamic translator generates better code than
-QEMU (in particular it does register allocation) but it is closely tied
-to an x86 host.
-
-EM86 [4] is the closest project to QEMU (and QEMU still uses some of its
-code, in particular the ELF file loader). EM86 was limited to an alpha
-host and used a proprietary and slow interpreter (the interpreter part
-of the FX!32 Digital Win32 code translator [5]).
+support for it (QEMU could be used to detect out of bound memory
+accesses as Valgrind, but it has no support to track uninitialised data
+as Valgrind does). The Valgrind dynamic translator generates better code
+than QEMU (in particular it does register allocation) but it is closely
+tied to an x86 host and target and has no support for precise exceptions
+and system emulation.
+
+EM86 [4] is the closest project to user space QEMU (and QEMU still uses
+some of its code, in particular the ELF file loader). EM86 was limited
+to an alpha host and used a proprietary and slow interpreter (the
+interpreter part of the FX!32 Digital Win32 code translator [5]).
TWIN [6] is a Windows API emulator like Wine. It is less accurate than
Wine but includes a protected mode x86 interpreter to launch x86 Windows
because all the data structures and function parameters exchanged
between the API and the x86 code must be converted.
+User mode Linux [7] was the only solution before QEMU to launch a Linux
+kernel as a process while not needing any host kernel patches. However,
+user mode Linux requires heavy kernel patches while QEMU accepts
+unpatched Linux kernels. It would be interesting to compare the
+performance of the two approaches.
+
+The new Plex86 [8] PC virtualizer is done in the same spirit as the QEMU
+system emulator. It requires a patched Linux kernel to work (you cannot
+launch the same kernel on your PC), but the patches are really small. As
+it is a PC virtualizer (no emulation is done except for some priveledged
+instructions), it has the potential of being faster than QEMU. The
+downside is that a complicated (and potentially unsafe) host kernel
+patch is needed.
+
@section Portable dynamic translation
QEMU is a dynamic translator. When it first encounters a piece of code,
it converts it to the host instruction set. Usually dynamic translators
-are very complicated and highly CPU dependant. QEMU uses some tricks
+are very complicated and highly CPU dependent. QEMU uses some tricks
which make it relatively easily portable and simple while achieving good
performances.
a linked list of every translated block contained in a given page. Other
linked lists are also maintained to undo direct block chaining.
-Althought the overhead of doing @code{mprotect()} calls is important,
+Although the overhead of doing @code{mprotect()} calls is important,
most MSDOS programs can be emulated at reasonnable speed with QEMU and
DOSEMU.
@section Self-virtualization
-QEMU was conceived so that ultimately it can emulate itself. Althought
+QEMU was conceived so that ultimately it can emulate itself. Although
it is not very useful, it is an important test to show the power of the
emulator.
shared object as the ld-linux.so ELF interpreter. That way, it can be
relocated at load time.
+@section MMU emulation
+
+For system emulation, QEMU uses the mmap() system call to emulate the
+target CPU MMU. It works as long the emulated OS does not use an area
+reserved by the host OS (such as the area above 0xc0000000 on x86
+Linux).
+
+It is planned to add a slower but more precise MMU emulation
+with a software MMU.
+
@section Bibliography
@table @asis
@url{http://www.willows.com/}, Windows API library emulation from
Willows Software.
+@item [7]
+@url{http://user-mode-linux.sourceforge.net/},
+The User-mode Linux Kernel.
+
+@item [8]
+@url{http://www.plex86.org/},
+The new Plex86 project.
+
@end table
@chapter Regression Tests
-In the directory @file{tests/}, various interesting x86 testing programs
+In the directory @file{tests/}, various interesting testing programs
are available. There are used for regression testing.
-@section @file{hello}
+@section @file{hello-i386}
Very simple statically linked x86 program, just to test QEMU during a
port to a new host CPU.
+@section @file{hello-arm}
+
+Very simple statically linked ARM program, just to test QEMU during a
+port to a new host CPU.
+
@section @file{test-i386}
This program executes most of the 16 bit and 32 bit x86 instructions and
projects / qemu / blobdiff