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648fe157d3
One common thing that device emulation does is manipulate bitmasks, for example to check whether two bitmaps have common bits. One example in the pl011 crate is the checks for pending interrupts, where an interrupt cause corresponds to at least one interrupt source from a fixed set. Unfortunately, this is one case where Rust *can* provide some kind of abstraction but it does so with a rather Perl-ish There Is More Way To Do It. It is not something where a crate like "bilge" helps, because it only covers the packing of bits in a structure; operations like "are all bits of Y set in X" almost never make sense for bit-packed structs; you need something else, there are several crates that do it and of course we're going to roll our own. In particular I examined three: - bitmask (https://docs.rs/bitmask/0.5.0/bitmask/) does not support const at all. This is a showstopper because one of the ugly things in the current pl011 code is the ugliness of code that defines interrupt masks at compile time: pub const E: Self = Self(Self::OE.0 | Self::BE.0 | Self::PE.0 | Self::FE.0); or even worse: const IRQMASK: [u32; 6] = [ Interrupt::E.0 | Interrupt::MS.0 | Interrupt::RT.0 | Interrupt::TX.0 | Interrupt::RX.0, ... } You would have to use roughly the same code---"bitmask" only helps with defining the struct. - bitmask_enum (https://docs.rs/bitmask-enum/2.2.5/bitmask_enum/) does not have a good separation of "valid" and "invalid" bits, so for example "!x" will invert all 16 bits if you choose u16 as the representation -- even if you only defined 10 bits. This makes it easier to introduce subtle bugs in comparisons. - bitflags (https://docs.rs/bitflags/2.6.0/bitflags/) is generally the most used such crate and is the one that I took most inspiration from with respect to the syntax. It's a pretty sophisticated implementation, with a lot of bells and whistles such as an implementation of "Iter" that returns the bits one at a time. The main thing that all of them lack, however, is a way to simplify the ugly definitions like the above. "bitflags" includes const methods that perform AND/OR/XOR of masks (these are necessary because Rust operator overloading does not support const yet, and therefore overloaded operators cannot be used in the definition of a "static" variable), but they become even more verbose and unmanageable, like Interrupt::E.union(Interrupt::MS).union(Interrupt::RT).union(Interrupt::TX).union(Interrupt::RX) This was the main reason to create "bits", which allows something like bits!(Interrupt: E | MS | RT | TX | RX) and expands it 1) add "Interrupt::" in front of all identifiers 2) convert operators to the wordy const functions like "union". It supports boolean operators "&", "|", "^", "!" and parentheses, with a relatively simple recursive descent parser that's implemented in qemu_api_macros. Since I don't remember exactly how the macro was developed, I cannot exclude that it contains code from "bitflags". Therefore, I am conservatively leaving in the MIT and Apache 2.0 licenses from bitflags. In fact, I think there would be a benefit in being able to push code back to "bitflags" anyway whenever applicable, so that the two libraries do not diverge too much, so that's another reason to use this. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> |
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=========== QEMU README =========== QEMU is a generic and open source machine & userspace emulator and virtualizer. QEMU is capable of emulating a complete machine in software without any need for hardware virtualization support. By using dynamic translation, it achieves very good performance. QEMU can also integrate with the Xen and KVM hypervisors to provide emulated hardware while allowing the hypervisor to manage the CPU. With hypervisor support, QEMU can achieve near native performance for CPUs. When QEMU emulates CPUs directly it is capable of running operating systems made for one machine (e.g. an ARMv7 board) on a different machine (e.g. an x86_64 PC board). QEMU is also capable of providing userspace API virtualization for Linux and BSD kernel interfaces. This allows binaries compiled against one architecture ABI (e.g. the Linux PPC64 ABI) to be run on a host using a different architecture ABI (e.g. the Linux x86_64 ABI). This does not involve any hardware emulation, simply CPU and syscall emulation. QEMU aims to fit into a variety of use cases. It can be invoked directly by users wishing to have full control over its behaviour and settings. It also aims to facilitate integration into higher level management layers, by providing a stable command line interface and monitor API. It is commonly invoked indirectly via the libvirt library when using open source applications such as oVirt, OpenStack and virt-manager. QEMU as a whole is released under the GNU General Public License, version 2. For full licensing details, consult the LICENSE file. Documentation ============= Documentation can be found hosted online at `<https://www.qemu.org/documentation/>`_. The documentation for the current development version that is available at `<https://www.qemu.org/docs/master/>`_ is generated from the ``docs/`` folder in the source tree, and is built by `Sphinx <https://www.sphinx-doc.org/en/master/>`_. Building ======== QEMU is multi-platform software intended to be buildable on all modern Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety of other UNIX targets. The simple steps to build QEMU are: .. code-block:: shell mkdir build cd build ../configure make Additional information can also be found online via the QEMU website: * `<https://wiki.qemu.org/Hosts/Linux>`_ * `<https://wiki.qemu.org/Hosts/Mac>`_ * `<https://wiki.qemu.org/Hosts/W32>`_ Submitting patches ================== The QEMU source code is maintained under the GIT version control system. .. code-block:: shell git clone https://gitlab.com/qemu-project/qemu.git When submitting patches, one common approach is to use 'git format-patch' and/or 'git send-email' to format & send the mail to the qemu-devel@nongnu.org mailing list. All patches submitted must contain a 'Signed-off-by' line from the author. Patches should follow the guidelines set out in the `style section <https://www.qemu.org/docs/master/devel/style.html>`_ of the Developers Guide. Additional information on submitting patches can be found online via the QEMU website: * `<https://wiki.qemu.org/Contribute/SubmitAPatch>`_ * `<https://wiki.qemu.org/Contribute/TrivialPatches>`_ The QEMU website is also maintained under source control. .. code-block:: shell git clone https://gitlab.com/qemu-project/qemu-web.git * `<https://www.qemu.org/2017/02/04/the-new-qemu-website-is-up/>`_ A 'git-publish' utility was created to make above process less cumbersome, and is highly recommended for making regular contributions, or even just for sending consecutive patch series revisions. It also requires a working 'git send-email' setup, and by default doesn't automate everything, so you may want to go through the above steps manually for once. For installation instructions, please go to: * `<https://github.com/stefanha/git-publish>`_ The workflow with 'git-publish' is: .. code-block:: shell $ git checkout master -b my-feature $ # work on new commits, add your 'Signed-off-by' lines to each $ git publish Your patch series will be sent and tagged as my-feature-v1 if you need to refer back to it in the future. Sending v2: .. code-block:: shell $ git checkout my-feature # same topic branch $ # making changes to the commits (using 'git rebase', for example) $ git publish Your patch series will be sent with 'v2' tag in the subject and the git tip will be tagged as my-feature-v2. Bug reporting ============= The QEMU project uses GitLab issues to track bugs. Bugs found when running code built from QEMU git or upstream released sources should be reported via: * `<https://gitlab.com/qemu-project/qemu/-/issues>`_ If using QEMU via an operating system vendor pre-built binary package, it is preferable to report bugs to the vendor's own bug tracker first. If the bug is also known to affect latest upstream code, it can also be reported via GitLab. For additional information on bug reporting consult: * `<https://wiki.qemu.org/Contribute/ReportABug>`_ ChangeLog ========= For version history and release notes, please visit `<https://wiki.qemu.org/ChangeLog/>`_ or look at the git history for more detailed information. Contact ======= The QEMU community can be contacted in a number of ways, with the two main methods being email and IRC: * `<mailto:qemu-devel@nongnu.org>`_ * `<https://lists.nongnu.org/mailman/listinfo/qemu-devel>`_ * #qemu on irc.oftc.net Information on additional methods of contacting the community can be found online via the QEMU website: * `<https://wiki.qemu.org/Contribute/StartHere>`_