qemu-tech.texi - qemu - Git at Google

 @node Implementation notes
 @appendix Implementation notes

 @menu
 * CPU emulation::
 * Translator Internals::
 * QEMU compared to other emulators::
 * Managed start up options::
 * Bibliography::
 @end menu

 @node CPU emulation
 @section CPU emulation

 @menu
 * 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

 @node x86
 @subsection x86 and x86-64 emulation

 QEMU x86 target features:

 @itemize

 @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. There is some support for MMX/3DNow!, SSE, SSE2, SSE3, SSSE3,
 and SSE4 as well as x86-64 SVM.

 @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.

 @end itemize

 Current QEMU limitations:

 @itemize

 @item Limited x86-64 support.

 @item IPC syscalls are missing.

 @item The x86 segment limits and access rights are not tested at every
 memory access (yet). Hopefully, very few OSes seem to rely on that for
 normal use.

 @end itemize

 @node ARM
 @subsection ARM emulation

 @itemize

 @item Full ARM 7 user emulation.

 @item NWFPE FPU support included in user Linux emulation.

 @item Can run most ARM Linux binaries.

 @end itemize

 @node MIPS
 @subsection MIPS emulation

 @itemize

 @item The system emulation allows full MIPS32/MIPS64 Release 2 emulation,
 including privileged instructions, FPU and MMU, in both little and big
 endian modes.

 @item The Linux userland emulation can run many 32 bit MIPS Linux binaries.

 @end itemize

 Current QEMU limitations:

 @itemize

 @item Self-modifying code is not always handled correctly.

 @item 64 bit userland emulation is not implemented.

 @item The system emulation is not complete enough to run real firmware.

 @item The watchpoint debug facility is not implemented.

 @end itemize

 @node PPC
 @subsection PowerPC emulation

 @itemize

 @item Full PowerPC 32 bit emulation, including privileged instructions,
 FPU and MMU.

 @item Can run most PowerPC Linux binaries.

 @end itemize

 @node SPARC
 @subsection Sparc32 and Sparc64 emulation

 @itemize

 @item Full SPARC V8 emulation, including privileged
 instructions, FPU and MMU. SPARC V9 emulation includes most privileged
 and VIS instructions, FPU and I/D MMU. Alignment is fully enforced.

 @item Can run most 32-bit SPARC Linux binaries, SPARC32PLUS Linux binaries and
 some 64-bit SPARC Linux binaries.

 @end itemize

 Current QEMU limitations:

 @itemize

 @item IPC syscalls are missing.

 @item Floating point exception support is buggy.

 @item Atomic instructions are not correctly implemented.

 @item There are still some problems with Sparc64 emulators.

 @end itemize

 @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,
 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.

 @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 New core configuration that requires no additional instructions
 may be created from overlay with minimal amount of hand-written code.

 @end itemize

 @node Managed start up options
 @section Managed start up options

 In system mode emulation, it's possible to create a VM in a paused state using
 the -S command line option. In this state the machine is completely initialized
 according to command line options and ready to execute VM code but VCPU threads
 are not executing any code. The VM state in this paused state depends on the way
 QEMU was started. It could be in:
 @table @asis
 @item initial state (after reset/power on state)
 @item with direct kernel loading, the initial state could be amended to execute
 code loaded by QEMU in the VM's RAM and with incoming migration
 @item with incoming migration, initial state will by amended with the migrated
 machine state after migration completes.
 @end table

 This paused state is typically used by users to query machine state and/or
 additionally configure the machine (by hotplugging devices) in runtime before
 allowing VM code to run.

 However, at the -S pause point, it's impossible to configure options that affect
 initial VM creation (like: -smp/-m/-numa ...) or cold plug devices. The
 experimental --preconfig command line option  allows pausing QEMU
 before the initial VM creation, in a ``preconfig'' state, where additional
 queries and configuration can be performed via QMP before moving on to
 the resulting configuration startup. In the preconfig state, QEMU only allows
 a limited set of commands over the QMP monitor, where the commands do not
 depend on an initialized machine, including but not limited to:
 @table @asis
 @item qmp_capabilities
 @item query-qmp-schema
 @item query-commands
 @item query-status
 @item x-exit-preconfig
 @end table
	@node Implementation notes
	@appendix Implementation notes

	@menu
	* CPU emulation::
	* Translator Internals::
	* QEMU compared to other emulators::
	* Managed start up options::
	* Bibliography::
	@end menu

	@node CPU emulation
	@section CPU emulation

	@menu
	* 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

	@node x86
	@subsection x86 and x86-64 emulation

	QEMU x86 target features:

	@itemize

	@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. There is some support for MMX/3DNow!, SSE, SSE2, SSE3, SSSE3,
	and SSE4 as well as x86-64 SVM.

	@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.

	@end itemize

	Current QEMU limitations:

	@itemize

	@item Limited x86-64 support.

	@item IPC syscalls are missing.

	@item The x86 segment limits and access rights are not tested at every
	memory access (yet). Hopefully, very few OSes seem to rely on that for
	normal use.

	@end itemize

	@node ARM
	@subsection ARM emulation

	@itemize

	@item Full ARM 7 user emulation.

	@item NWFPE FPU support included in user Linux emulation.

	@item Can run most ARM Linux binaries.

	@end itemize

	@node MIPS
	@subsection MIPS emulation

	@itemize

	@item The system emulation allows full MIPS32/MIPS64 Release 2 emulation,
	including privileged instructions, FPU and MMU, in both little and big
	endian modes.

	@item The Linux userland emulation can run many 32 bit MIPS Linux binaries.

	@end itemize

	Current QEMU limitations:

	@itemize

	@item Self-modifying code is not always handled correctly.

	@item 64 bit userland emulation is not implemented.

	@item The system emulation is not complete enough to run real firmware.

	@item The watchpoint debug facility is not implemented.

	@end itemize

	@node PPC
	@subsection PowerPC emulation

	@itemize

	@item Full PowerPC 32 bit emulation, including privileged instructions,
	FPU and MMU.

	@item Can run most PowerPC Linux binaries.

	@end itemize

	@node SPARC
	@subsection Sparc32 and Sparc64 emulation

	@itemize

	@item Full SPARC V8 emulation, including privileged
	instructions, FPU and MMU. SPARC V9 emulation includes most privileged
	and VIS instructions, FPU and I/D MMU. Alignment is fully enforced.

	@item Can run most 32-bit SPARC Linux binaries, SPARC32PLUS Linux binaries and
	some 64-bit SPARC Linux binaries.

	@end itemize

	Current QEMU limitations:

	@itemize

	@item IPC syscalls are missing.

	@item Floating point exception support is buggy.

	@item Atomic instructions are not correctly implemented.

	@item There are still some problems with Sparc64 emulators.

	@end itemize

	@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,
	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.

	@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 New core configuration that requires no additional instructions
	may be created from overlay with minimal amount of hand-written code.

	@end itemize

	@node Managed start up options
	@section Managed start up options

	In system mode emulation, it's possible to create a VM in a paused state using
	the -S command line option. In this state the machine is completely initialized
	according to command line options and ready to execute VM code but VCPU threads
	are not executing any code. The VM state in this paused state depends on the way
	QEMU was started. It could be in:
	@table @asis
	@item initial state (after reset/power on state)
	@item with direct kernel loading, the initial state could be amended to execute
	code loaded by QEMU in the VM's RAM and with incoming migration
	@item with incoming migration, initial state will by amended with the migrated
	machine state after migration completes.
	@end table

	This paused state is typically used by users to query machine state and/or
	additionally configure the machine (by hotplugging devices) in runtime before
	allowing VM code to run.

	However, at the -S pause point, it's impossible to configure options that affect
	initial VM creation (like: -smp/-m/-numa ...) or cold plug devices. The
	experimental --preconfig command line option allows pausing QEMU
	before the initial VM creation, in a ``preconfig'' state, where additional
	queries and configuration can be performed via QMP before moving on to
	the resulting configuration startup. In the preconfig state, QEMU only allows
	a limited set of commands over the QMP monitor, where the commands do not
	depend on an initialized machine, including but not limited to:
	@table @asis
	@item qmp_capabilities
	@item query-qmp-schema
	@item query-commands
	@item query-status
	@item x-exit-preconfig
	@end table