Rustlantis

A Rust Mid-level Intermediate Representation fuzzer

It can generate custom MIR programs containing:

• All primitive integer and floating point types, bool, char, arrays, tuples, references, raw pointers, structs, and enums.
• Functions containing multiple basic blocks
• Terminators: Goto, Return, SwitchInt (match), Call.
• Intrinsic functions: arith_offset (for pointer arithmetics), transmute, bswap, fmaf64.
• Operators: all arithmetic, logical and bitwise operations on integers and floating points, and checked arithmetic (Add, Sub, Mul) on integers
• All primitive literal expressions, as well as tuple, array, and struct aggregate expressions
• Creating references and raw pointers, and dereferencing them
• Casts between integers, floating points, char, and bool

Generated programs are terminating, UB-free, and deterministic. A discrepancy between testing backends always indicate a bug in them (or a bug in Rustlantis).

Requirements

• Rust nightly
• rustup

Config

Install Miri and Cranelift with Rustup rustup component add miri rustc-codegen-cranelift-preview, then copy config.toml.example to config.toml

Usage

To generate and difftest one seed, run

./fuzz-one.sh <seed>

A program will be generated to $TMPDIR and tested. If difftest passes (no bug), it will exit with 0. If difftest spots a difference between testing backends, it will exit with 1 and save the reproduction file to ./repros/.

To generate a program only, run generate

Usage: generate [OPTIONS] <seed>

Arguments:
  <seed>  generation seed

Options:
  -d, --debug                      generate a program where values are printed instead of hashed (slow)
      --call-syntax <call-syntax>  switch between different versions of Call syntaxes [default: v4] [possible values: v1, v2, v3, v4]
  -h, --help                       Print help
  -V, --version                    Print version

To difftest an existing program, run difftest

Usage: difftest <file>

Arguments:
  <file>  

Options:
  -h, --help  Print help

Quirks

• Cranelift not supported on AArch64 macOS: https://github.com/bjorn3/rustc_codegen_cranelift/issues/1248
• rustc_codegen_gcc can be used as a backend, but it doesn't support enough language features yet to be usable

Namesake

The Space Shuttle Atlantis docked with Mir space station seven times: https://en.wikipedia.org/wiki/Shuttle%E2%80%93Mir_program

Trophies

🦀: Root cause in Rust 🐉: Root cause in LLVM 🏗️: Root cause in Cranelift

Crashes & ICEs

• 🦀 RenameReturnPlace is broken: rust-lang/rust#110902
• 🦀 ReferencePropagation prevents partial initialisation: rust-lang/rust#111426
• 🐉 phi nodes assumed to be non-empty: llvm/llvm-project#63013
• 🐉 Assertion failure in RegisterCoalescer: llvm/llvm-project#63033
• 🦀 MIR inlining inserts statements at the wrong place: rust-lang/rust#117355
• 🏗️ Overflowing shift triggers panic in Cranelift: rust-lang/rustc_codegen_cranelift#1455 & bytecodealliance/wasmtime#7865

Silent Miscompilations

• 🦀 ConstProp propagates over mutating borrows: rust-lang/rust#110947
• 🦀 *const T in function parameters annotated with readonly: rust-lang/rust#111502
• 🐉 Aliasing analysis merges loads from different offsets: rust-lang/rust#112061 & llvm/llvm-project#63019
• 🐉 Constant folding produces invalid boolean values: rust-lang/rust#112170 & llvm/llvm-project#63055
• 🐉 Aliasing analysis broken for overflowing pointer offsets: rust-lang/rust#112526 & llvm/llvm-project#63266
• rust-lang/rust#112548
• 🐉 Copy elision corrupts stack arguments with two parts: rust-lang/rust#112767 & llvm/llvm-project#63430
• 🐉 Copy elision reads stack arguments from the wrong offsets: llvm/llvm-project#63475
• 🦀 Subnormal f64 to f32 cast is wrong: rust-lang/rust#113407
• 🐉 AST size merging is wrong: llvm/llvm-project#64897
• 🦀 ConstProp propagates over assignment of unknown values: rust-lang/rust#118328
• 🐉 Bad undef/poison handling in InstCombine: llvm/llvm-project#74890
• 🦀 GVN merges moved function arguments: rust-lang/rust#120613
• 🐉 GVNPass forgets to remove poison generating flags: llvm/llvm-project#82884
• 🏗️ Misoptimization of imul + ireduce: rust-lang/rustc_codegen_cranelift#1460 & bytecodealliance/wasmtime#7999
• 🐉 InstCombine calculates wrong insertelement instructions: rust-lang/rust#121996 & llvm/llvm-project#84025

Previously known bugs

• 🦀 Const eval gives x % x wrong sign when x is a negative float: rust-lang/rust#109567 (first reported rust-lang/rust#102403)
• 🐉 Write to dangling pointer is hoisted outside of condition: rust-lang/rust#112213 (first reported llvm/llvm-project#51838)