ChangeLog/7.2

System emulation

Incompatible changes

Consult the 'Removed features' page for details of suggested replacement functionality.

Removal of the "slirp" submodule (affects "-netdev user")

The "slirp" submodule / code (which is the code behind "-netdev user" / "-nic user") has been removed from the QEMU source tree, so you now need to install your distributions libslirp development package before compiling QEMU to get the user-mode networking feature included again. For example, if you see an error message like this:

Parameter 'type' expects a netdev backend type

... this might be caused by the missing "user" mode backend. In that case, please install libslirp first ("dnf install libslirp-devel" on Fedora and "apt-get install libslirp-dev" on Debian for example), recompile your QEMU with --enable-slirp, then try again.

Semihosting calls from userspace

For some target architectures (arm, m68k, mips, nios2, riscv, xtensa) QEMU supports a "semihosting" style ABI where guest code can make calls to directly print messages, read and write host files, and so on. Handling of when this is enabled in system emulation has been made consistent across target architectures. By default it is not enabled; if enabled via the commandline "-semihosting" or "-semihosting-config enable=on" then it is only permitted from non-userspace guest code; if the new-in-7.2 "-semihosting-config userspace=on" option is given then it is also permitted from guest userspace. For some target architectures this is a change in behaviour: mips, nios2 and xtensa previously allowed userspace access by default, and riscv allowed all access by default. If you were using semihosting on these targets and relying on that previous default behaviour, you need to update your commandline to explicitly enable semihosting to the desired level.

Other removed features

• The -watchdog option has been removed, use -device instead.

New deprecated options and features

• Big endian 32-bit MIPS hosts are now deprecated due to lack of CI coverage.

Consult the "Deprecated Features" chapter of the QEMU System Emulation User's Guide for further details of the deprecations and their suggested replacements.

Arm

• The following CPU architecture features are now emulated:
  • FEAT_ETS (Enhanced Translation Synchronization)
  • FEAT_PMUv3p5 (PMU Extensions v3.5)
• New emulated CPU types:
  • Cortex-A35

MIPS

• deprecated 32 bit big endian host

OpenRISC

• Stability improvements
• Performance improvements by supporting MTTCG
• New virt platform is added to assist with CI and device testing

RISC-V

ISA and Extensions

• Update [m|h]tinst CSR in interrupt handling
• Force disable extensions if priv spec version does not match
• fix shifts shamt value for rv128c
• move zmmul out of the experimental
• Add checks for supported extension combinations
• Fix typo and restore Pointer Masking functionality for RISC-V
• Add mask agnostic behaviour (rvv_ma_all_1s) for vector extension
• Add Zihintpause support
• Add xicondops in ISA entry
• Use official extension names for AIA CSRs
• Fix the CSR check for cycle{h}, instret{h}, time{h}, hpmcounter3-31{h}
• Improvements to the RISC-V debugger spec

Machines

• virt: pass random seed to fdt
• opentitan: bump opentitan version
• virt machine device tree improvements
• Allow setting the resetvec for the OpenTitan machine

Fixes and Misc

• Upgrade OpenSBI to v1.1
• microchip_pfsoc: fix kernel panics due to missing peripherals
• Remove additional priv version check for mcountinhibit
• Fixup register addresses for Ibex SPI
• Cleanup the RISC-V virt machine documentation
• Remove fixed numbering from GDB xml feature files

s390x

• Fix emulation of LZRF instruction
• Implement Message-Security-Assist Extension 5 (random number generation via PRNO instruction)
• Implement SHA-512 via KIMD/KLMD instructions
• Enhanced zPCI interpretation support for KVM guests

x86

• Support for passing a random seed to the Linux kernel when booted with -kernel
• Support for the MSR_CORE_THREAD_COUNT MSR

TCG

• Performance improvements in full-system emulation
• Fixes in SSE implementation

KVM

• Support for the "notify vmexit" mechanism, preventing processor bugs from hanging the whole system, through the -accel kvm,notify-vmexit= and -accel kvm,notify-window= options

Device emulation and assignment

Network devices

• Fixed bug that could cause a stack or heap overflow with the emulated "tulip" NIC (CVE-2022-2962)

SCSI

• Support for setting CD-ROM block size using the physical-block-size property of the scsi-cd device.

Character devices

• UNIX socket support on Windows has been added

GUI

• On macOS systems, the same QEMU binary can include both the Cocoa user interface and the SDL or GTK+ user interfaces.

Network

• The "slirp" submodule has been removed from the QEMU source tree. Use libslirp from your OS distribution instead.

Semihosting

Semihosting calls were generally not permitted for userspace guest code in system emulation. This can now be enabled with the "-semihosting-config userspace=on" option. Note that the usual remarks about semihosting apply -- because it permits direct guest access to the host filesystem, it should only be used with trusted guest binaries.

User-mode emulation

• Dump failing executable on CPU exception
• support for system calls pidfd_open(), pidfd_send_signal() and pidfd_getfd()
• support for FUTEX_WAKE_BITSET and PI futexes
• support for madvise(MADV_DONTNEED) on file mappings

HPPA

• Increased guest stack to 80MB
• Fix signal handling
• Add vDSO emulation and thus avoid an executable stack
• Changed guest memory layout like on real hppa kernel

x86

• The qemu-i386 and qemu-x86_64 binaries now default to the 'max' CPU model instead of 'qemu32' / 'qemu64'
• Support for saving/restoring SSE registers in signal frames in qemu-i386 (when FXSR is set in CPUID)
• Support for saving/restoring XSAVE state in signal frames (when XSAVE is set in CPUID)

Guest agent

• The "--blacklist" command line option has been renamed to "--block-rpcs". The old version is still supported for now, but will be removed in the future; "-b" can be used on old and new versions alike.

Build Information

Python

• Python 3.7 or newer is now required.

GIT submodules

• The libslirp library is not included in QEMU anymore. The development packages for libslirp must be installed in the system to build QEMU with user-mode networking support.

Container Based Builds

• All containers are now "flat" containers (often generated by lci-tool)

Build Dependencies

• Meson 0.61 or newer is now required. QEMU ships with Meson 0.61.5, which will be used if necessary.

Known issues

• see Planning/7.2