ChangeLog/4.0

System emulation

Incompatible changes

• The "handle" option to -fsdev and -virtfs has been removed. The "local" or "proxy" options should be used instead.

New deprecated options and features

Consult the "Deprecated Features" appendix for the full list of historically deprecated features/options.

Arm

• Allow AArch64 processors to boot from a kernel placed over 4GB into RAM
• arm: Implement the ARMv8.1-HPD extension
• arm: Implement the ARMv8.2-AA32HPD extension
• arm: Implement the ARMv8.1-LOR extension (as the trivial "no limited ordering regions provided" minimum)
• The micro:bit board supports more devices: timer, GPIO and RNG
• The cubieboard model now implements the 'A' SRAM
• The BLK_MAX register in the TZ MPC device now reports the correct value
• The u-boot "noload" image type is now supported for the Arm virt board

MIPS

• Build for MIPS n32 hosts fixed.

s390

• vfio-ap now no longer inhibits usage of memory ballooners

Device emulation and assignment

Network devices

• pvrdma: Add support for RDMA MAD

Crypto subsystem

• The block storage encryption backends are now capable of using multiple threads for encryption/decryption

Monitor

• QMP can now execute a few commands "out of band". This is useful for postcopy recovery. For details, see docs/interop/qmp-spec.txt.
• query-qmp-schema reflects QEMU's build configuration more closely. For instance, stuff related to replication is properly absent when QEMU was built with --disable-replication.
• QMP events SHUTDOWN and RESET now carry a reason
• New QMP command query-current-machine
• QMP/HMP command system_wakeup now fails when the guest isn't suspended, or doesn't even support suspend.
• QMP/HMP command `cpu-add` is now deprecated

Block devices and tools

• Improved tracing and error diagnostics for NBD code
• Fix infinite loop in DMG image format

Miscellaneous

• QEMU's builting gdbstub now supports the gdb multiprocess extension. Boards which have more than one cluster of CPUs (like the 'xlnx-zcu102' board when run with '-smp 6') will report them as being two processes (each of which has one thread per CPU in the cluster). You will need at least GDB 7.2. Attach to QEMU with a GDB command sequence like:

target extended :1234

add-inferior

inferior 2

attach 2

and then the "info threads" command should show 2 processes.

TCG

• SoftFloat acceleration - where it is safe to do so the softfloat helpers will use the host FPU instructions yeilding significant performance increases

Build Information

Build Dependencies

• QEMU now requires at least GCC version 4.8 or Clang version 3.4 (or Clang from Xcode 5.1) to be built

Known issues

• see Planning/4.0