riscv/qemu: QEMU main repository: Please see https://www.qemu.org/docs/master/devel/submitting-a-patch.html for how to submit changes to QEMU. Pull Requests are ignored. Please only use release tarballs from the QEMU website. http://www.qemu.org - qemu

QEMU main repository: Please see https://www.qemu.org/docs/master/devel/submitting-a-patch.html for how to submit changes to QEMU. Pull Requests are ignored. Please only use release tarballs from the QEMU website. http://www.qemu.org

emulation kvm qemu virtualization

History

Paolo Bonzini 648fe157d3 rust: add "bits", a custom bitflags implementation 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>		10 months ago
..
src	rust: add "bits", a custom bitflags implementation	10 months ago
Cargo.toml	rust: add "bits", a custom bitflags implementation	10 months ago
meson.build	rust: add "bits", a custom bitflags implementation	10 months ago