QEMU User space emulator

Supported Operating Systems

The following OS are supported in user space emulation:

  • Linux (referred as qemu-linux-user)
  • BSD (referred as qemu-bsd-user)

Features

QEMU user space emulation has the following notable features:

System call translation:
QEMU includes a generic system call translator. This means that the parameters of the system calls can be converted to fix endianness and 32/64-bit mismatches between hosts and targets. IOCTLs can be converted too.
POSIX signal handling:

QEMU can redirect to the running program all signals coming from the host (such as SIGALRM), as well as synthesize signals from virtual CPU exceptions (for example SIGFPE when the program executes a division by zero).

QEMU relies on the host kernel to emulate most signal system calls, for example to emulate the signal mask. On Linux, QEMU supports both normal and real-time signals.

Threading:
On Linux, QEMU can emulate the clone syscall and create a real host thread (with a separate virtual CPU) for each emulated thread. Note that not all targets currently emulate atomic operations correctly. x86 and Arm use a global lock in order to preserve their semantics.

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.

Linux User space emulator

Quick Start

In order to launch a Linux process, QEMU needs the process executable itself and all the target (x86) dynamic libraries used by it.

  • On x86, you can just try to launch any process by using the native libraries:

    qemu-i386 -L / /bin/ls
    

    -L / tells that the x86 dynamic linker must be searched with a / prefix.

  • Since QEMU is also a linux process, you can launch QEMU with QEMU (NOTE: you can only do that if you compiled QEMU from the sources):

    qemu-i386 -L / qemu-i386 -L / /bin/ls
    
  • On non x86 CPUs, you need first to download at least an x86 glibc (qemu-runtime-i386-XXX-.tar.gz on the QEMU web page). Ensure that LD_LIBRARY_PATH is not set:

    unset LD_LIBRARY_PATH
    

    Then you can launch the precompiled ls x86 executable:

    qemu-i386 tests/i386/ls
    

    You can look at scripts/qemu-binfmt-conf.sh so that QEMU is automatically launched by the Linux kernel when you try to launch x86 executables. It requires the binfmt_misc module in the Linux kernel.

  • The x86 version of QEMU is also included. You can try weird things such as:

    qemu-i386 /usr/local/qemu-i386/bin/qemu-i386 \
              /usr/local/qemu-i386/bin/ls-i386
    

Wine launch

  • Ensure that you have a working QEMU with the x86 glibc distribution (see previous section). In order to verify it, you must be able to do:

    qemu-i386 /usr/local/qemu-i386/bin/ls-i386
    
  • Download the binary x86 Wine install (qemu-XXX-i386-wine.tar.gz on the QEMU web page).

  • Configure Wine on your account. Look at the provided script /usr/local/qemu-i386/bin/wine-conf.sh. Your previous ${HOME}/.wine directory is saved to ${HOME}/.wine.org.

  • Then you can try the example putty.exe:

    qemu-i386 /usr/local/qemu-i386/wine/bin/wine \
              /usr/local/qemu-i386/wine/c/Program\ Files/putty.exe
    

Command line options

qemu-i386 [-h] [-d] [-L path] [-s size] [-cpu model] [-g port] [-B offset] [-R size] program [arguments...]
-h
Print the help
-L path
Set the x86 elf interpreter prefix (default=/usr/local/qemu-i386)
-s size
Set the x86 stack size in bytes (default=524288)
-cpu model
Select CPU model (-cpu help for list and additional feature selection)
-E var=value
Set environment var to value.
-U var
Remove var from the environment.
-B offset
Offset guest address by the specified number of bytes. This is useful when the address region required by guest applications is reserved on the host. This option is currently only supported on some hosts.
-R size
Pre-allocate a guest virtual address space of the given size (in bytes). “G”, “M”, and “k” suffixes may be used when specifying the size.

Debug options:

-d item1,...
Activate logging of the specified items (use ‘-d help’ for a list of log items)
-p pagesize
Act as if the host page size was ‘pagesize’ bytes
-g port
Wait gdb connection to port
-singlestep
Run the emulation in single step mode.

Environment variables:

QEMU_STRACE
Print system calls and arguments similar to the ‘strace’ program (NOTE: the actual ‘strace’ program will not work because the user space emulator hasn’t implemented ptrace). At the moment this is incomplete. All system calls that don’t have a specific argument format are printed with information for six arguments. Many flag-style arguments don’t have decoders and will show up as numbers.

Other binaries

user mode (Alpha) qemu-alpha TODO.

user mode (Arm) qemu-armeb TODO.

user mode (Arm) qemu-arm is also capable of running Arm “Angel” semihosted ELF binaries (as implemented by the arm-elf and arm-eabi Newlib/GDB configurations), and arm-uclinux bFLT format binaries.

user mode (ColdFire) user mode (M68K) qemu-m68k is capable of running semihosted binaries using the BDM (m5xxx-ram-hosted.ld) or m68k-sim (sim.ld) syscall interfaces, and coldfire uClinux bFLT format binaries.

The binary format is detected automatically.

user mode (Cris) qemu-cris TODO.

user mode (i386) qemu-i386 TODO. qemu-x86_64 TODO.

user mode (Microblaze) qemu-microblaze TODO.

user mode (MIPS) qemu-mips executes 32-bit big endian MIPS binaries (MIPS O32 ABI).

qemu-mipsel executes 32-bit little endian MIPS binaries (MIPS O32 ABI).

qemu-mips64 executes 64-bit big endian MIPS binaries (MIPS N64 ABI).

qemu-mips64el executes 64-bit little endian MIPS binaries (MIPS N64 ABI).

qemu-mipsn32 executes 32-bit big endian MIPS binaries (MIPS N32 ABI).

qemu-mipsn32el executes 32-bit little endian MIPS binaries (MIPS N32 ABI).

user mode (NiosII) qemu-nios2 TODO.

user mode (PowerPC) qemu-ppc64abi32 TODO. qemu-ppc64 TODO. qemu-ppc TODO.

user mode (SH4) qemu-sh4eb TODO. qemu-sh4 TODO.

user mode (SPARC) qemu-sparc can execute Sparc32 binaries (Sparc32 CPU, 32 bit ABI).

qemu-sparc32plus can execute Sparc32 and SPARC32PLUS binaries (Sparc64 CPU, 32 bit ABI).

qemu-sparc64 can execute some Sparc64 (Sparc64 CPU, 64 bit ABI) and SPARC32PLUS binaries (Sparc64 CPU, 32 bit ABI).

BSD User space emulator

BSD Status

  • target Sparc64 on Sparc64: Some trivial programs work.

Quick Start

In order to launch a BSD process, QEMU needs the process executable itself and all the target dynamic libraries used by it.

  • On Sparc64, you can just try to launch any process by using the native libraries:

    qemu-sparc64 /bin/ls
    

Command line options

qemu-sparc64 [-h] [-d] [-L path] [-s size] [-bsd type] program [arguments...]
-h
Print the help
-L path
Set the library root path (default=/)
-s size
Set the stack size in bytes (default=524288)
-ignore-environment
Start with an empty environment. Without this option, the initial environment is a copy of the caller’s environment.
-E var=value
Set environment var to value.
-U var
Remove var from the environment.
-bsd type
Set the type of the emulated BSD Operating system. Valid values are FreeBSD, NetBSD and OpenBSD (default).

Debug options:

-d item1,...
Activate logging of the specified items (use ‘-d help’ for a list of log items)
-p pagesize
Act as if the host page size was ‘pagesize’ bytes
-singlestep
Run the emulation in single step mode.