util/oslib-posix.c: Avoid warning on NetBSD

[qemu.git] / qemu-tech.texi

diff --git a/qemu-tech.texi b/qemu-tech.texi
index d73dda8e35a019a917e913a84f5954b24a119dc5..52a56ae25ec042f23c4da93435e9c591eca88078 100644 (file)
--- a/qemu-tech.texi
+++ b/qemu-tech.texi
@@ -1,147 +1,27 @@
-\input texinfo @c -*- texinfo -*-
-@c %**start of header
-@setfilename qemu-tech.info
-
-@documentlanguage en
-@documentencoding UTF-8
-
-@settitle QEMU Internals
-@exampleindent 0
-@paragraphindent 0
-@c %**end of header
-
-@ifinfo
-@direntry
-* QEMU Internals: (qemu-tech).   The QEMU Emulator Internals.
-@end direntry
-@end ifinfo
-
-@iftex
-@titlepage
-@sp 7
-@center @titlefont{QEMU Internals}
-@sp 3
-@end titlepage
-@end iftex
-
-@ifnottex
-@node Top
-@top
+@node Implementation notes
+@appendix Implementation notes

 
 @menu
 
 @menu

-* Introduction::
-* QEMU Internals::
-* Regression Tests::
-* Index::
+* CPU emulation::
+* Translator Internals::
+* QEMU compared to other emulators::
+* Bibliography::

 @end menu
 @end menu

-@end ifnottex
-
-@contents

 
 

-@node Introduction
-@chapter Introduction
+@node CPU emulation
+@section CPU emulation

 
 @menu
 
 @menu

-* intro_features::         Features
-* intro_x86_emulation::    x86 and x86-64 emulation
-* intro_arm_emulation::    ARM emulation
-* intro_mips_emulation::   MIPS emulation
-* intro_ppc_emulation::    PowerPC emulation
-* intro_sparc_emulation::  Sparc32 and Sparc64 emulation
-* intro_xtensa_emulation:: Xtensa emulation
-* intro_other_emulation::  Other CPU emulation
+* x86::     x86 and x86-64 emulation
+* ARM::     ARM emulation
+* MIPS::    MIPS emulation
+* PPC::     PowerPC emulation
+* SPARC::   Sparc32 and Sparc64 emulation
+* Xtensa::  Xtensa emulation

 @end menu
 
 @end menu
 

-@node intro_features
-@section Features
-
-QEMU is a FAST! processor emulator using a portable dynamic
-translator.
-
-QEMU has two operating modes:
-
-@itemize @minus
-
-@item
-Full system emulation. In this mode (full platform virtualization),
-QEMU emulates a full system (usually a PC), including a processor and
-various peripherals. It can be used to launch several different
-Operating Systems at once without rebooting the host machine or to
-debug system code.
-
-@item
-User mode emulation. In this mode (application level virtualization),
-QEMU can launch processes compiled for one CPU on another CPU, however
-the Operating Systems must match. This can be used for example 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.
-
-QEMU generic features:
-
-@itemize
-
-@item User space only or full system emulation.
-
-@item Using dynamic translation to native code for reasonable speed.
-
-@item
-Working on x86, x86_64 and PowerPC32/64 hosts. Being tested on ARM,
-HPPA, Sparc32 and Sparc64. Previous versions had some support for
-Alpha and S390 hosts, but TCG (see below) doesn't support those yet.
-
-@item Self-modifying code support.
-
-@item Precise exceptions support.
-
-@item
-Floating point library supporting both full software emulation and
-native host FPU instructions.
-
-@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
-
-Linux user emulator (Linux host only) can be used to launch the Wine
-Windows API emulator (@url{http://www.winehq.org}). A BSD user emulator for BSD
-hosts is under development. It would also be possible to develop a
-similar user emulator for Solaris.
-
-QEMU full system emulation features:
-@itemize
-@item
-QEMU uses a full software MMU for maximum portability.
-
-@item
-QEMU can optionally use an in-kernel accelerator, like kvm. The accelerators 
-execute some of the guest code natively, while
-continuing to emulate the rest of the machine.
-
-@item
-Various hardware devices can be emulated and in some cases, host
-devices (e.g. serial and parallel ports, USB, drives) can be used
-transparently by the guest Operating System. Host device passthrough
-can be used for talking to external physical peripherals (e.g. a
-webcam, modem or tape drive).
-
-@item
-Symmetric multiprocessing (SMP) even on a host with a single CPU. On a
-SMP host system, QEMU can use only one CPU fully due to difficulty in
-implementing atomic memory accesses efficiently.
-
-@end itemize
-
-@node intro_x86_emulation
-@section x86 and x86-64 emulation
+@node x86
+@subsection x86 and x86-64 emulation

 
 QEMU x86 target features:
 
 
 QEMU x86 target features:
 


@@ -175,8 +55,8 @@ normal use.
 
 @end itemize
 
 
 @end itemize
 

-@node intro_arm_emulation
-@section ARM emulation
+@node ARM
+@subsection ARM emulation

 
 @itemize
 
 
 @itemize
 


@@ -188,8 +68,8 @@ normal use.
 
 @end itemize
 
 
 @end itemize
 

-@node intro_mips_emulation
-@section MIPS emulation
+@node MIPS
+@subsection MIPS emulation

 
 @itemize
 
 
 @itemize
 


@@ -215,8 +95,8 @@ Current QEMU limitations:
 
 @end itemize
 
 
 @end itemize
 

-@node intro_ppc_emulation
-@section PowerPC emulation
+@node PPC
+@subsection PowerPC emulation

 
 @itemize
 
 
 @itemize
 


@@ -227,8 +107,8 @@ FPU and MMU.
 
 @end itemize
 
 
 @end itemize
 

-@node intro_sparc_emulation
-@section Sparc32 and Sparc64 emulation
+@node SPARC
+@subsection Sparc32 and Sparc64 emulation

 
 @itemize
 
 
 @itemize
 


@@ -255,23 +135,23 @@ Current QEMU limitations:
 
 @end itemize
 
 
 @end itemize
 

-@node intro_xtensa_emulation
-@section Xtensa emulation
+@node Xtensa
+@subsection Xtensa emulation

 
 @itemize
 
 @item Core Xtensa ISA emulation, including most options: code density,
 loop, extended L32R, 16- and 32-bit multiplication, 32-bit division,
 
 @itemize
 
 @item Core Xtensa ISA emulation, including most options: code density,
 loop, extended L32R, 16- and 32-bit multiplication, 32-bit division,

-MAC16, miscellaneous operations, boolean, multiprocessor synchronization,
+MAC16, miscellaneous operations, boolean, FP coprocessor, coprocessor
+context, debug, multiprocessor synchronization,

 conditional store, exceptions, relocatable vectors, unaligned exception,
 interrupts (including high priority and timer), hardware alignment,
 region protection, region translation, MMU, windowed registers, thread
 pointer, processor ID.
 
 conditional store, exceptions, relocatable vectors, unaligned exception,
 interrupts (including high priority and timer), hardware alignment,
 region protection, region translation, MMU, windowed registers, thread
 pointer, processor ID.
 

-@item Not implemented options: FP coprocessor, coprocessor context,
-data/instruction cache (including cache prefetch and locking), XLMI,
-processor interface, debug. Also options not covered by the core ISA
-(e.g. FLIX, wide branches) are not implemented.
+@item Not implemented options: data/instruction cache (including cache
+prefetch and locking), XLMI, processor interface. Also options not
+covered by the core ISA (e.g. FLIX, wide branches) are not implemented.

 
 @item Can run most Xtensa Linux binaries.
 
 
 @item Can run most Xtensa Linux binaries.
 


@@ -280,96 +160,8 @@ may be created from overlay with minimal amount of hand-written code.
 
 @end itemize
 
 
 @end itemize
 

-@node intro_other_emulation
-@section Other CPU emulation
-
-In addition to the above, QEMU supports emulation of other CPUs with
-varying levels of success. These are:
-
-@itemize
-
-@item
-Alpha
-@item
-CRIS
-@item
-M68k
-@item
-SH4
-@end itemize
-
-@node QEMU Internals
-@chapter QEMU Internals
-
-@menu
-* QEMU compared to other emulators::
-* Portable dynamic translation::
-* Condition code optimisations::
-* CPU state optimisations::
-* Translation cache::
-* Direct block chaining::
-* Self-modifying code and translated code invalidation::
-* Exception support::
-* MMU emulation::
-* Device emulation::
-* Hardware interrupts::
-* User emulation specific details::
-* Bibliography::
-@end menu
-
-@node QEMU compared to other emulators
-@section QEMU compared to other emulators
-
-Like bochs [3], QEMU emulates an x86 CPU. But QEMU is much faster than
-bochs as it uses dynamic compilation. Bochs is closely tied to x86 PC
-emulation while QEMU can emulate several processors.
-
-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). 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
-executables. Such an approach has greater potential because most of the
-Windows API is executed natively but it is far more difficult to develop
-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. The price to pay is that QEMU is
-slower.
-
-The Plex86 [8] PC virtualizer is done in the same spirit as the now
-obsolete qemu-fast 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 privileged instructions), it has the potential of
-being faster than QEMU. The downside is that a complicated (and
-potentially unsafe) host kernel patch is needed.
-
-The commercial PC Virtualizers (VMWare [9], VirtualPC [10], TwoOStwo
-[11]) are faster than QEMU, but they all need specific, proprietary
-and potentially unsafe host drivers. Moreover, they are unable to
-provide cycle exact simulation as an emulator can.
-
-VirtualBox [12], Xen [13] and KVM [14] are based on QEMU. QEMU-SystemC
-[15] uses QEMU to simulate a system where some hardware devices are
-developed in SystemC.
-
-@node Portable dynamic translation
-@section Portable dynamic translation
+@node Translator Internals
+@section Translator Internals

 
 QEMU is a dynamic translator. When it first encounters a piece of code,
 it converts it to the host instruction set. Usually dynamic translators
 
 QEMU is a dynamic translator. When it first encounters a piece of code,
 it converts it to the host instruction set. Usually dynamic translators


@@ -377,70 +169,28 @@ are very complicated and highly CPU dependent. QEMU uses some tricks
 which make it relatively easily portable and simple while achieving good
 performances.
 
 which make it relatively easily portable and simple while achieving good
 performances.
 

-After the release of version 0.9.1, QEMU switched to a new method of
-generating code, Tiny Code Generator or TCG. TCG relaxes the
-dependency on the exact version of the compiler used. The basic idea
-is to split every target instruction into a couple of RISC-like TCG
-ops (see @code{target-i386/translate.c}). Some optimizations can be
-performed at this stage, including liveness analysis and trivial
-constant expression evaluation. TCG ops are then implemented in the
-host CPU back end, also known as TCG target (see
-@code{tcg/i386/tcg-target.c}). For more information, please take a
-look at @code{tcg/README}.
-
-@node Condition code optimisations
-@section Condition code optimisations
-
-Lazy evaluation of CPU condition codes (@code{EFLAGS} register on x86)
-is important for CPUs where every instruction sets the condition
-codes. It tends to be less important on conventional RISC systems
-where condition codes are only updated when explicitly requested. On
-Sparc64, costly update of both 32 and 64 bit condition codes can be
-avoided with lazy evaluation.
-
-Instead of computing the condition codes after each x86 instruction,
-QEMU just stores one operand (called @code{CC_SRC}), the result
-(called @code{CC_DST}) and the type of operation (called
-@code{CC_OP}). When the condition codes are needed, the condition
-codes can be calculated using this information. In addition, an
-optimized calculation can be performed for some instruction types like
-conditional branches.
-
-@code{CC_OP} is almost never explicitly set in the generated code
-because it is known at translation time.
-
-The lazy condition code evaluation is used on x86, m68k, cris and
-Sparc. ARM uses a simplified variant for the N and Z flags.
-
-@node CPU state optimisations
-@section CPU state optimisations
+QEMU's dynamic translation backend is called TCG, for "Tiny Code
+Generator". For more information, please take a look at @code{tcg/README}.

 
 

+Some notable features of QEMU's dynamic translator are:
+
+@table @strong
+
+@item CPU state optimisations:

 The target CPUs have many internal states which change the way it
 evaluates instructions. In order to achieve a good speed, the
 translation phase considers that some state information of the virtual
 CPU cannot change in it. The state is recorded in the Translation
 Block (TB). If the state changes (e.g. privilege level), a new TB will
 be generated and the previous TB won't be used anymore until the state
 The target CPUs have many internal states which change the way it
 evaluates instructions. In order to achieve a good speed, the
 translation phase considers that some state information of the virtual
 CPU cannot change in it. The state is recorded in the Translation
 Block (TB). If the state changes (e.g. privilege level), a new TB will
 be generated and the previous TB won't be used anymore until the state

-matches the state recorded in the previous TB. For example, if the SS,
+matches the state recorded in the previous TB. The same idea can be applied
+to other aspects of the CPU state.  For example, on x86, if the SS,

 DS and ES segments have a zero base, then the translator does not even
 generate an addition for the segment base.
 
 DS and ES segments have a zero base, then the translator does not even
 generate an addition for the segment base.
 

-[The FPU stack pointer register is not handled that way yet].
-
-@node Translation cache
-@section Translation cache
-
-A 32 MByte cache holds the most recently used translations. For
-simplicity, it is completely flushed when it is full. A translation unit
-contains just a single basic block (a block of x86 instructions
-terminated by a jump or by a virtual CPU state change which the
-translator cannot deduce statically).
-
-@node Direct block chaining
-@section Direct block chaining
-
+@item Direct block chaining:

 After each translated basic block is executed, QEMU uses the simulated
 After each translated basic block is executed, QEMU uses the simulated

-Program Counter (PC) and other cpu state informations (such as the CS
+Program Counter (PC) and other cpu state information (such as the CS

 segment base value) to find the next basic block.
 
 In order to accelerate the most common cases where the new simulated PC
 segment base value) to find the next basic block.
 
 In order to accelerate the most common cases where the new simulated PC


@@ -452,18 +202,17 @@ it easier to make the jump target modification atomic. On some host
 architectures (such as x86 or PowerPC), the @code{JUMP} opcode is
 directly patched so that the block chaining has no overhead.
 
 architectures (such as x86 or PowerPC), the @code{JUMP} opcode is
 directly patched so that the block chaining has no overhead.
 

-@node Self-modifying code and translated code invalidation
-@section Self-modifying code and translated code invalidation
-
+@item Self-modifying code and translated code invalidation:

 Self-modifying code is a special challenge in x86 emulation because no
 instruction cache invalidation is signaled by the application when code
 is modified.
 
 Self-modifying code is a special challenge in x86 emulation because no
 instruction cache invalidation is signaled by the application when code
 is modified.
 

-When translated code is generated for a basic block, the corresponding
-host page is write protected if it is not already read-only. Then, if
-a write access is done to the page, Linux raises a SEGV signal. QEMU
-then invalidates all the translated code in the page and enables write
-accesses to the page.
+User-mode emulation marks a host page as write-protected (if it is
+not already read-only) every time translated code is generated for a
+basic block.  Then, if a write access is done to the page, Linux raises
+a SEGV signal. QEMU then invalidates all the translated code in the page
+and enables write accesses to the page.  For system emulation, write
+protection is achieved through the software MMU.

 
 Correct translated code invalidation is done efficiently by maintaining
 a linked list of every translated block contained in a given page. Other
 
 Correct translated code invalidation is done efficiently by maintaining
 a linked list of every translated block contained in a given page. Other


@@ -475,132 +224,95 @@ necessary. However, QEMU still requires that the generated code always
 matches the target instructions in memory in order to handle
 exceptions correctly.
 
 matches the target instructions in memory in order to handle
 exceptions correctly.
 

-@node Exception support
-@section Exception support
-
+@item Exception support:

 longjmp() is used when an exception such as division by zero is
 encountered.
 
 The host SIGSEGV and SIGBUS signal handlers are used to get invalid
 longjmp() is used when an exception such as division by zero is
 encountered.
 
 The host SIGSEGV and SIGBUS signal handlers are used to get invalid

-memory accesses. The simulated program counter is found by
-retranslating the corresponding basic block and by looking where the
-host program counter was at the exception point.
-
-The virtual CPU cannot retrieve the exact @code{EFLAGS} register because
-in some cases it is not computed because of condition code
-optimisations. It is not a big concern because the emulated code can
-still be restarted in any cases.
-
-@node MMU emulation
-@section MMU emulation
-
-For system emulation QEMU supports a soft MMU. In that mode, the MMU
+memory accesses.  QEMU keeps a map from host program counter to
+target program counter, and looks up where the exception happened
+based on the host program counter at the exception point.
+
+On some targets, some bits of the virtual CPU's state are not flushed to the
+memory until the end of the translation block.  This is done for internal
+emulation state that is rarely accessed directly by the program and/or changes
+very often throughout the execution of a translation block---this includes
+condition codes on x86, delay slots on SPARC, conditional execution on
+ARM, and so on.  This state is stored for each target instruction, and
+looked up on exceptions.
+
+@item MMU emulation:
+For system emulation QEMU uses a software MMU. In that mode, the MMU

 virtual to physical address translation is done at every memory
 virtual to physical address translation is done at every memory

-access. QEMU uses an address translation cache to speed up the
-translation.
+access.

 
 

+QEMU uses an address translation cache (TLB) to speed up the translation.

 In order to avoid flushing the translated code each time the MMU
 In order to avoid flushing the translated code each time the MMU

-mappings change, QEMU uses a physically indexed translation cache. It
+mappings change, all caches in QEMU are physically indexed.  This

 means that each basic block is indexed with its physical address.
 
 means that each basic block is indexed with its physical address.
 

-When MMU mappings change, only the chaining of the basic blocks is
-reset (i.e. a basic block can no longer jump directly to another one).
-
-@node Device emulation
-@section Device emulation
-
-Systems emulated by QEMU are organized by boards. At initialization
-phase, each board instantiates a number of CPUs, devices, RAM and
-ROM. Each device in turn can assign I/O ports or memory areas (for
-MMIO) to its handlers. When the emulation starts, an access to the
-ports or MMIO memory areas assigned to the device causes the
-corresponding handler to be called.
-
-RAM and ROM are handled more optimally, only the offset to the host
-memory needs to be added to the guest address.
-
-The video RAM of VGA and other display cards is special: it can be
-read or written directly like RAM, but write accesses cause the memory
-to be marked with VGA_DIRTY flag as well.
-
-QEMU supports some device classes like serial and parallel ports, USB,
-drives and network devices, by providing APIs for easier connection to
-the generic, higher level implementations. The API hides the
-implementation details from the devices, like native device use or
-advanced block device formats like QCOW.
+In order to avoid invalidating the basic block chain when MMU mappings
+change, chaining is only performed when the destination of the jump
+shares a page with the basic block that is performing the jump.

 
 

-Usually the devices implement a reset method and register support for
-saving and loading of the device state. The devices can also use
-timers, especially together with the use of bottom halves (BHs).
-
-@node Hardware interrupts
-@section Hardware interrupts
-
-In order to be faster, QEMU does not check at every basic block if a
-hardware interrupt is pending. Instead, the user must asynchronously
-call a specific function to tell that an interrupt is pending. This
-function resets the chaining of the currently executing basic
-block. It ensures that the execution will return soon in the main loop
-of the CPU emulator. Then the main loop can test if the interrupt is
-pending and handle it.
-
-@node User emulation specific details
-@section User emulation specific details
-
-@subsection Linux system call translation
-
-QEMU includes a generic system call translator for Linux. It means that
-the parameters of the system calls can be converted to fix the
-endianness and 32/64 bit issues. The IOCTLs are converted with a generic
-type description system (see @file{ioctls.h} and @file{thunk.c}).
-
-QEMU supports host CPUs which have pages bigger than 4KB. It records all
-the mappings the process does and try to emulated the @code{mmap()}
-system calls in cases where the host @code{mmap()} call would fail
-because of bad page alignment.
-
-@subsection Linux signals
-
-Normal and real-time signals are queued along with their information
-(@code{siginfo_t}) as it is done in the Linux kernel. Then an interrupt
-request is done to the virtual CPU. When it is interrupted, one queued
-signal is handled by generating a stack frame in the virtual CPU as the
-Linux kernel does. The @code{sigreturn()} system call is emulated to return
-from the virtual signal handler.
+The MMU can also distinguish RAM and ROM memory areas from MMIO memory
+areas.  Access is faster for RAM and ROM because the translation cache also
+hosts the offset between guest address and host memory.  Accessing MMIO
+memory areas instead calls out to C code for device emulation.
+Finally, the MMU helps tracking dirty pages and pages pointed to by
+translation blocks.
+@end table

 
 

-Some signals (such as SIGALRM) directly come from the host. Other
-signals are synthesized from the virtual CPU exceptions such as SIGFPE
-when a division by zero is done (see @code{main.c:cpu_loop()}).
+@node QEMU compared to other emulators
+@section QEMU compared to other emulators

 
 

-The blocked signal mask is still handled by the host Linux kernel so
-that most signal system calls can be redirected directly to the host
-Linux kernel. Only the @code{sigaction()} and @code{sigreturn()} system
-calls need to be fully emulated (see @file{signal.c}).
+Like bochs [1], QEMU emulates an x86 CPU. But QEMU is much faster than
+bochs as it uses dynamic compilation. Bochs is closely tied to x86 PC
+emulation while QEMU can emulate several processors.

 
 

-@subsection clone() system call and threads
+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). 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.

 
 

-The Linux clone() system call is usually used to create a thread. QEMU
-uses the host clone() system call so that real host threads are created
-for each emulated thread. One virtual CPU instance is created for each
-thread.
+EM86 [3] 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 [4]).

 
 

-The virtual x86 CPU atomic operations are emulated with a global lock so
-that their semantic is preserved.
+TWIN from Willows Software was a Windows API emulator like Wine. It is less
+accurate than Wine but includes a protected mode x86 interpreter to launch
+x86 Windows executables. Such an approach has greater potential because most
+of the Windows API is executed natively but it is far more difficult to
+develop because all the data structures and function parameters exchanged
+between the API and the x86 code must be converted.

 
 

-Note that currently there are still some locking issues in QEMU. In
-particular, the translated cache flush is not protected yet against
-reentrancy.
+User mode Linux [5] 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. The price to pay is that QEMU is
+slower.

 
 

-@subsection Self-virtualization
+The Plex86 [6] PC virtualizer is done in the same spirit as the now
+obsolete qemu-fast 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 privileged instructions), it has the potential of
+being faster than QEMU. The downside is that a complicated (and
+potentially unsafe) host kernel patch is needed.

 
 

-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.
+The commercial PC Virtualizers (VMWare [7], VirtualPC [8]) are faster
+than QEMU (without virtualization), but they all need specific, proprietary
+and potentially unsafe host drivers. Moreover, they are unable to
+provide cycle exact simulation as an emulator can.

 
 

-Achieving self-virtualization is not easy because there may be address
-space conflicts. QEMU user emulators solve this problem by being an
-executable ELF shared object as the ld-linux.so ELF interpreter. That
-way, it can be relocated at load time.
+VirtualBox [9], Xen [10] and KVM [11] are based on QEMU. QEMU-SystemC
+[12] uses QEMU to simulate a system where some hardware devices are
+developed in SystemC.

 
 @node Bibliography
 @section Bibliography
 
 @node Bibliography
 @section Bibliography


@@ -608,105 +320,52 @@ way, it can be relocated at load time.
 @table @asis
 
 @item [1]
 @table @asis
 
 @item [1]

-@url{http://citeseer.nj.nec.com/piumarta98optimizing.html}, Optimizing
-direct threaded code by selective inlining (1998) by Ian Piumarta, Fabio
-Riccardi.
+@url{http://bochs.sourceforge.net/}, the Bochs IA-32 Emulator Project,
+by Kevin Lawton et al.

 
 @item [2]
 
 @item [2]

-@url{http://developer.kde.org/~sewardj/}, Valgrind, an open-source
-memory debugger for x86-GNU/Linux, by Julian Seward.
+@url{http://www.valgrind.org/}, Valgrind, an open-source memory debugger
+for GNU/Linux.

 
 @item [3]
 
 @item [3]

-@url{http://bochs.sourceforge.net/}, the Bochs IA-32 Emulator Project,
-by Kevin Lawton et al.
+@url{http://ftp.dreamtime.org/pub/linux/Linux-Alpha/em86/v0.2/docs/em86.html},
+the EM86 x86 emulator on Alpha-Linux.

 
 @item [4]
 
 @item [4]

-@url{http://www.cs.rose-hulman.edu/~donaldlf/em86/index.html}, the EM86
-x86 emulator on Alpha-Linux.
-
-@item [5]

 @url{http://www.usenix.org/publications/library/proceedings/usenix-nt97/@/full_papers/chernoff/chernoff.pdf},
 DIGITAL FX!32: Running 32-Bit x86 Applications on Alpha NT, by Anton
 Chernoff and Ray Hookway.
 
 @url{http://www.usenix.org/publications/library/proceedings/usenix-nt97/@/full_papers/chernoff/chernoff.pdf},
 DIGITAL FX!32: Running 32-Bit x86 Applications on Alpha NT, by Anton
 Chernoff and Ray Hookway.
 

-@item [6]
-@url{http://www.willows.com/}, Windows API library emulation from
-Willows Software.
-
-@item [7]
+@item [5]

 @url{http://user-mode-linux.sourceforge.net/},
 The User-mode Linux Kernel.
 
 @url{http://user-mode-linux.sourceforge.net/},
 The User-mode Linux Kernel.
 

-@item [8]
+@item [6]

 @url{http://www.plex86.org/},
 The new Plex86 project.
 
 @url{http://www.plex86.org/},
 The new Plex86 project.
 

-@item [9]
+@item [7]

 @url{http://www.vmware.com/},
 The VMWare PC virtualizer.
 
 @url{http://www.vmware.com/},
 The VMWare PC virtualizer.
 

-@item [10]
-@url{http://www.microsoft.com/windowsxp/virtualpc/},
+@item [8]
+@url{https://www.microsoft.com/download/details.aspx?id=3702},

 The VirtualPC PC virtualizer.
 
 The VirtualPC PC virtualizer.
 

-@item [11]
-@url{http://www.twoostwo.org/},
-The TwoOStwo PC virtualizer.
-
-@item [12]
+@item [9]

 @url{http://virtualbox.org/},
 The VirtualBox PC virtualizer.
 
 @url{http://virtualbox.org/},
 The VirtualBox PC virtualizer.
 

-@item [13]
+@item [10]

 @url{http://www.xen.org/},
 The Xen hypervisor.
 
 @url{http://www.xen.org/},
 The Xen hypervisor.
 

-@item [14]
-@url{http://kvm.qumranet.com/kvmwiki/Front_Page},
+@item [11]
+@url{http://www.linux-kvm.org/},

 Kernel Based Virtual Machine (KVM).
 
 Kernel Based Virtual Machine (KVM).
 

-@item [15]
+@item [12]

 @url{http://www.greensocs.com/projects/QEMUSystemC},
 QEMU-SystemC, a hardware co-simulator.
 
 @end table
 @url{http://www.greensocs.com/projects/QEMUSystemC},
 QEMU-SystemC, a hardware co-simulator.
 
 @end table

-
-@node Regression Tests
-@chapter Regression Tests
-
-In the directory @file{tests/}, various interesting testing programs
-are available. They are used for regression testing.
-
-@menu
-* test-i386::
-* linux-test::
-@end menu
-
-@node test-i386
-@section @file{test-i386}
-
-This program executes most of the 16 bit and 32 bit x86 instructions and
-generates a text output. It can be compared with the output obtained with
-a real CPU or another emulator. The target @code{make test} runs this
-program and a @code{diff} on the generated output.
-
-The Linux system call @code{modify_ldt()} is used to create x86 selectors
-to test some 16 bit addressing and 32 bit with segmentation cases.
-
-The Linux system call @code{vm86()} is used to test vm86 emulation.
-
-Various exceptions are raised to test most of the x86 user space
-exception reporting.
-
-@node linux-test
-@section @file{linux-test}
-
-This program tests various Linux system calls. It is used to verify
-that the system call parameters are correctly converted between target
-and host CPUs.
-
-@node Index
-@chapter Index
-@printindex cp
-
-@bye