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## yaxpeax-x86
x86 decoders implemented as part of the yaxpeax project.
`yaxpeax-x86` implements traits provided by `yaxpeax-arch`, which are likely how you want to use this library from Rust. included in the `ffi/` directory is a repackaging of `yaxpeax-x86` suitable for use by non-Rust callers, such as C or C++.
### features
* `#[no_std]`
* configurable choice of permitted instruction set extensions
* very fast
* pretty small?
### `#[no_std]`
the decoders provided by `yaxpeax-x86` are designed to be usable in a `no_std` setting, and does so by default. to build `yaxpeax_x86` decoders in `no_std` you'll want to set `default-features = false` as with many other `no_std` Rust crates. serde currently (though it doesn't seem _necessarily_?) relies on `std`, as well as the `colors` feature to render instructions with default (eg terminal-friendly) syntax highlighting.
### instruction set extensions
`yaxpeax-x86` decoders provide the option to specify what [instruction set extensions](http://git.iximeow.net/yaxpeax-x86/tree/src/long_mode/mod.rs#n1297) are eligible when decoding, to support decoding x86 instructions as understood by a particular microarchitecture. the default impls of decoders in `yaxpeax_x86` take an optimistsic approach to decoding and assumes all feature sets are available, as well as accepting both intel-specific and amd-specific quirks around undefined encodings.
### very fast
by the in-repo benchmark, `yaxpeax_x86::long_mode` decodes `x86_64` instructions at anywhere between 60 million instructions per second to just shy of 100 million instructions per second, depending on hardware and distribution of instructions being decoded.
when hooked up to [`disas-bench`](https://github.com/iximeow/disas-bench#results), `yaxpeax_x86::long_mode` has shown roughly 175mb/s decode throughput and on most hardware is the fastest software x86 decoder available.
### pretty small?
`yaxpeax_x86::long_mode` is expected to be around 20kb of code and data. currently a stripped static build of `ffi/` takes a bit more space - around 130kb. instruction rendering is currently non-optional, and is a significant amount of `.text` size. data tables are larger than anticipated, and it's currently an open question if they can be reduced down, or the size target of `yaxpeax_x86::long_mode` should be raised.
this, however, does not by any means make this library the smallest `x86_64` decoder; [`zydis`](https://github.com/zyantific/zydis) handily beats `yaxpeax-x86` out, taking only 10kb in an -O3 build for benchmarking.
### mirrors
the canonical copy of `yaxpeax-x86` is at [https://git.iximeow.net/yaxpeax-x86/](https://git.iximeow.net/yaxpeax-x86/).
`yaxpeax-x86` is also mirrored on GitHub at [https://www.github.com/iximeow/yaxpeax-x86](https://www.github.com/iximeow/yaxpeax-x86).
### ! user beware !
* `yaxpeax-x86` will, but does not yet, have a decoder for real-mode `x86`. it is strongly recommended to use `<yaxpeax_x86::protected_mode::Arch as Arch>::Instruction` and similar type aliases, rather than using struct and operand types directly. user beware!
* avx512 is not yet supported. user beware!
* avx256 support is questionable. user beware!
* `ffi/` exists, and is enough to get a bare minimum decoding and string representation of an instruction, but is not as fully populated as a non-rust caller might like. user beware!
* `yaxpeax_x86` makes regular use of `unsafe { unreachable_unchecked(); }` and occasional use of `unsafe { _.get_unchecked() }`. while these are, to the author's knowledge, unreachable, this is audited and updated on a best-effort basis. eventually, `yaxpeax-x86` should grow a fuzzing suite that build with these cases checked and panicking.
### changelog
a changelog across crate versions is maintained in the `CHANGELOG` file located in the repo, as well as [online](https://git.iximeow.net/yaxpeax-x86/tree/CHANGELOG).
### see also
[`iced`](https://github.com/0xd4d/iced) is another very good `x86_64` decoder, also written in rust. it provides additional information about instruction semantics as part of the crate, as well as the ability to re-encode instructions.
[`disas-bench`](https://github.com/athre0z/disas-bench), a handy benchmark of several `x86_64` decoders, easily extended to compare with `yaxpeax-x86` as well.
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