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x86 decoders implemented as part of the yaxpeax project it is a mazing projec.

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++.


  • #[no_std]
  • configurable choice of permitted instruction set extensions
  • very fast
  • pretty small?


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 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, 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 handily beats yaxpeax-x86 out, taking only 10kb in an -O3 build for benchmarking.


the canonical copy of yaxpeax-x86 is at

yaxpeax-x86 is also mirrored on GitHub at

! 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.


a changelog across crate versions is maintained in the CHANGELOG file located in the repo, as well as online.

see also

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, a handy benchmark of several x86_64 decoders, easily extended to compare with yaxpeax-x86 as well.


x86 decoders for the yaxpeax project




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