Skip to content
x86 decoders for the yaxpeax project
Branch: master
Clone or download
Latest commit 114d3fe Jan 19, 2020
Type Name Latest commit message Commit time
Failed to load latest commit information.
ffi avoid needing to dynamically allocate in yaxpeax-x86 ffi Jan 16, 2020
src support "int imm8" instructions Jan 16, 2020
Cargo.toml bump yaxpeax-arch Jan 18, 2020
LICENSE add explicit license also Jan 13, 2020 update readme with no-std information, feature description, and some … Jan 16, 2020 only try to link capstone if we're using capstone Jan 13, 2020


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++.


  • #[no_std]
  • configurable choice of permitted instruction set extensions
  • seems to be pretty 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 yaxpeax_x86::InstDecoder takes 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.

pretty 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 disasm-bench, yaxpeax_x86::long_mode has shown roughly 150mb/s decode throughput.

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 this 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 !

  • while the decoder has the option to select instruction set extensions, it is entirely likely that some extensions are not yet properly rejected when the corresponding flag is disabled. user beware!
  • yaxpeax-x86 likely has many corners where it does not reject instructions it should. particularly likely is accepting a register operand where the corresponding instruction specifically only allows memory encodings - lea is a good example of this. user beware!
  • yaxpeax-x86 will, but does not yet, have decoders for protected-mode and real-mode x86. currently, yaxpeax-x86 assumes that it is decoding long mode x86_64 instructions. it is strongly recommended to use <yaxpeax_x86::x86_64 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!
  • ring-0 instructions have questionable support. user beware!
  • the only unsafe code in yaxpeax_x86 is instances of unsafe { unreachable_unchecked(); }. while these are, currently, all unreachable, this code should default to a fail-safe assertion fail, with unreachable_unchecked being an opt-in feature. user beware!

see also

iced looks to be another very good x86_64 decoder, with an in-progress translation to rust

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

You can’t perform that action at this time.