qemu-tech.texi

   1 @node Implementation notes
   2 @appendix Implementation notes
   3
   4 @menu
   5 * CPU emulation::
   6 * Translator Internals::
   7 * QEMU compared to other emulators::
   8 * Managed start up options::
   9 * Bibliography::
  10 @end menu
  11
  12 @node CPU emulation
  13 @section CPU emulation
  14
  15 @menu
  16 * x86::     x86 and x86-64 emulation
  17 * ARM::     ARM emulation
  18 * MIPS::    MIPS emulation
  19 * PPC::     PowerPC emulation
  20 * SPARC::   Sparc32 and Sparc64 emulation
  21 * Xtensa::  Xtensa emulation
  22 @end menu
  23
  24 @node x86
  25 @subsection x86 and x86-64 emulation
  26
  27 QEMU x86 target features:
  28
  29 @itemize
  30
  31 @item The virtual x86 CPU supports 16 bit and 32 bit addressing with segmentation.
  32 LDT/GDT and IDT are emulated. VM86 mode is also supported to run
  33 DOSEMU. There is some support for MMX/3DNow!, SSE, SSE2, SSE3, SSSE3,
  34 and SSE4 as well as x86-64 SVM.
  35
  36 @item Support of host page sizes bigger than 4KB in user mode emulation.
  37
  38 @item QEMU can emulate itself on x86.
  39
  40 @item An extensive Linux x86 CPU test program is included @file{tests/test-i386}.
  41 It can be used to test other x86 virtual CPUs.
  42
  43 @end itemize
  44
  45 Current QEMU limitations:
  46
  47 @itemize
  48
  49 @item Limited x86-64 support.
  50
  51 @item IPC syscalls are missing.
  52
  53 @item The x86 segment limits and access rights are not tested at every
  54 memory access (yet). Hopefully, very few OSes seem to rely on that for
  55 normal use.
  56
  57 @end itemize
  58
  59 @node ARM
  60 @subsection ARM emulation
  61
  62 @itemize
  63
  64 @item Full ARM 7 user emulation.
  65
  66 @item NWFPE FPU support included in user Linux emulation.
  67
  68 @item Can run most ARM Linux binaries.
  69
  70 @end itemize
  71
  72 @node MIPS
  73 @subsection MIPS emulation
  74
  75 @itemize
  76
  77 @item The system emulation allows full MIPS32/MIPS64 Release 2 emulation,
  78 including privileged instructions, FPU and MMU, in both little and big
  79 endian modes.
  80
  81 @item The Linux userland emulation can run many 32 bit MIPS Linux binaries.
  82
  83 @end itemize
  84
  85 Current QEMU limitations:
  86
  87 @itemize
  88
  89 @item Self-modifying code is not always handled correctly.
  90
  91 @item 64 bit userland emulation is not implemented.
  92
  93 @item The system emulation is not complete enough to run real firmware.
  94
  95 @item The watchpoint debug facility is not implemented.
  96
  97 @end itemize
  98
  99 @node PPC
 100 @subsection PowerPC emulation
 101
 102 @itemize
 103
 104 @item Full PowerPC 32 bit emulation, including privileged instructions,
 105 FPU and MMU.
 106
 107 @item Can run most PowerPC Linux binaries.
 108
 109 @end itemize
 110
 111 @node SPARC
 112 @subsection Sparc32 and Sparc64 emulation
 113
 114 @itemize
 115
 116 @item Full SPARC V8 emulation, including privileged
 117 instructions, FPU and MMU. SPARC V9 emulation includes most privileged
 118 and VIS instructions, FPU and I/D MMU. Alignment is fully enforced.
 119
 120 @item Can run most 32-bit SPARC Linux binaries, SPARC32PLUS Linux binaries and
 121 some 64-bit SPARC Linux binaries.
 122
 123 @end itemize
 124
 125 Current QEMU limitations:
 126
 127 @itemize
 128
 129 @item IPC syscalls are missing.
 130
 131 @item Floating point exception support is buggy.
 132
 133 @item Atomic instructions are not correctly implemented.
 134
 135 @item There are still some problems with Sparc64 emulators.
 136
 137 @end itemize
 138
 139 @node Xtensa
 140 @subsection Xtensa emulation
 141
 142 @itemize
 143
 144 @item Core Xtensa ISA emulation, including most options: code density,
 145 loop, extended L32R, 16- and 32-bit multiplication, 32-bit division,
 146 MAC16, miscellaneous operations, boolean, FP coprocessor, coprocessor
 147 context, debug, multiprocessor synchronization,
 148 conditional store, exceptions, relocatable vectors, unaligned exception,
 149 interrupts (including high priority and timer), hardware alignment,
 150 region protection, region translation, MMU, windowed registers, thread
 151 pointer, processor ID.
 152
 153 @item Not implemented options: data/instruction cache (including cache
 154 prefetch and locking), XLMI, processor interface. Also options not
 155 covered by the core ISA (e.g. FLIX, wide branches) are not implemented.
 156
 157 @item Can run most Xtensa Linux binaries.
 158
 159 @item New core configuration that requires no additional instructions
 160 may be created from overlay with minimal amount of hand-written code.
 161
 162 @end itemize
 163
 164 @node Managed start up options
 165 @section Managed start up options
 166
 167 In system mode emulation, it's possible to create a VM in a paused state using
 168 the -S command line option. In this state the machine is completely initialized
 169 according to command line options and ready to execute VM code but VCPU threads
 170 are not executing any code. The VM state in this paused state depends on the way
 171 QEMU was started. It could be in:
 172 @table @asis
 173 @item initial state (after reset/power on state)
 174 @item with direct kernel loading, the initial state could be amended to execute
 175 code loaded by QEMU in the VM's RAM and with incoming migration
 176 @item with incoming migration, initial state will by amended with the migrated
 177 machine state after migration completes.
 178 @end table
 179
 180 This paused state is typically used by users to query machine state and/or
 181 additionally configure the machine (by hotplugging devices) in runtime before
 182 allowing VM code to run.
 183
 184 However, at the -S pause point, it's impossible to configure options that affect
 185 initial VM creation (like: -smp/-m/-numa ...) or cold plug devices. The
 186 experimental --preconfig command line option  allows pausing QEMU
 187 before the initial VM creation, in a ``preconfig'' state, where additional
 188 queries and configuration can be performed via QMP before moving on to
 189 the resulting configuration startup. In the preconfig state, QEMU only allows
 190 a limited set of commands over the QMP monitor, where the commands do not
 191 depend on an initialized machine, including but not limited to:
 192 @table @asis
 193 @item qmp_capabilities
 194 @item query-qmp-schema
 195 @item query-commands
 196 @item query-status
 197 @item x-exit-preconfig
 198 @end table