update
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@283 c046a42c-6fe2-441c-8c8c-71466251a162
diff --git a/qemu-doc.texi b/qemu-doc.texi
index 1b27f7f..a113a23 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -11,35 +11,62 @@
@section Features
-QEMU is a FAST! processor emulator. Its purpose is to run Linux executables
-compiled for one architecture on another. For example, x86 Linux
-processes can be ran on PowerPC Linux architectures. 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.
+QEMU is a FAST! processor emulator. By using dynamic translation it
+achieves a reasonnable speed while being easy to port on new host
+CPUs.
+
+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.
QEMU generic features:
@itemize
-@item User space only emulation.
-
-@item Working on x86 and PowerPC hosts. Being tested on ARM, Sparc32, Alpha and S390.
+@item User space only or full system emulation.
@item Using dynamic translation to native code for reasonnable speed.
+@item Working on x86 and PowerPC hosts. Being tested on ARM, Sparc32, Alpha and S390.
+
+@item Self-modifying code support.
+
+@item Precise exception 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 target signals.
+@end itemize
+@end itemize
-@item Self-modifying code support.
-
-@item The virtual CPU is a library (@code{libqemu}) which can be used
-in other projects.
-
+QEMU full system emulation features:
+@itemize
+@item Using mmap() system calls to simulate the MMU
@end itemize
@section x86 emulation
@@ -49,11 +76,9 @@
@itemize
@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 to run DOSEMU.
+LDT/GDT and IDT are emulated. VM86 mode is also supported to run DOSEMU.
-@item Precise user space x86 exceptions.
-
-@item Support of host page sizes bigger than 4KB.
+@item Support of host page sizes bigger than 4KB in user mode emulation.
@item QEMU can emulate itself on x86.
@@ -73,12 +98,21 @@
@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
@section ARM emulation
@@ -94,7 +128,7 @@
@end itemize
-@chapter Invocation
+@chapter QEMU User space emulation invocation
@section Quick Start
@@ -198,27 +232,188 @@
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 an initrd (initial Ram Disk). 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 (bellard@voyager) (gcc version 2.95.2 20000220 (Debian GNU/Linux)) #42 Wed Jun 25 14:16:12 CEST 2003
+BIOS-provided physical RAM map:
+ BIOS-88: 0000000000000000 - 000000000009f000 (usable)
+ BIOS-88: 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/ram ramdisk_size=6144
+Initializing CPU#0
+Detected 501.785 MHz processor.
+Calibrating delay loop... 973.20 BogoMIPS
+Memory: 24776k/32768k available (725k kernel code, 7604k reserved, 151k data, 48k 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
+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 6144K 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 2048)
+NET4: Unix domain sockets 1.0/SMP for Linux NET4.0.
+RAMDISK: ext2 filesystem found at block 0
+RAMDISK: Loading 6144 blocks [1 disk] into ram disk... done.
+Freeing initrd memory: 6144k freed
+VFS: Mounted root (ext2 filesystem).
+Freeing unused kernel memory: 48k 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 @key{Ctrl-a b} is 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
+
+NOTE: the example initrd is a modified version of the one made by Kevin
+Lawton for the plex86 Project (@url{www.plex86.org}).
+
+@section Kernel Compilation
+
+You can use any Linux kernel within QEMU provided it is mapped at
+address 0x90000000 (the default is 0xc0000000). You must modify only two
+lines in the kernel source:
+
+In asm/page.h, replace
+@example
+#define __PAGE_OFFSET (0xc0000000)
+@end example
+by
+@example
+#define __PAGE_OFFSET (0x90000000)
+@end example
+
+And in arch/i386/vmlinux.lds, replace
+@example
+ . = 0xc0000000 + 0x100000;
+@end example
+by
+@example
+ . = 0x90000000 + 0x100000;
+@end example
+
+The file config-2.4.20 gives the configuration of the example kernel.
+
+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
+Serial port (port=0x3f8, irq=4)
+@item
+NE2000 network adapter (port=0x300, irq=9)
+@item
+Dumb VGA (to print the @code{uncompressing Linux kernel} message)
+@end itemize
+
@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 and target.
+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 and target and has no support for precise exception
+and system emulation.
-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]).
+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
@@ -227,6 +422,20 @@
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) kernel patch is
+needed.
+
@section Portable dynamic translation
QEMU is a dynamic translator. When it first encounters a piece of code,
@@ -409,6 +618,16 @@
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
@@ -439,6 +658,14 @@
@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
