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Sail RISC-V model
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RISCV Sail Model

This repository contains a model of the RISCV architecture written in Sail. It used to be contained in the Sail repository.

It currently defines enough of RV32IMAC and RV64IMAC to boot a conventional OS with a terminal output device. The model specifies assembly language formats of the instructions, the corresponding encoders and decoders, and the instruction semantics. The current status of its coverage of the prose RISC-V specification is summarized here. A reading guide to the model is provided in the doc/ subdirectory, along with a guide on how to extend the model.

Latex definitions can be generated from the model that are suitable for inclusion in reference documentation. Drafts of the RISC-V unprivileged and privileged specifications that include the Sail formal definitions are available in the sail branch of this risc-v-isa-manual repository.

This is one of several formal models compared within the RISC-V ISA Formal Spec Public Review.

Directory Structure

- model                   // Sail specification modules
- generated_definitions   // files generated by Sail, in RV32 and RV64 subdirectories
  -  c
  -  ocaml
  -  lem
  -  isabelle
  -  coq
  -  hol4
  -  latex
- prover_snapshots        // snapshots of generated theorem prover definitions
- handwritten_support     // prover support files
- c_emulator              // supporting platform files for C emulator
- ocaml_emulator          // supporting platform files for OCaml emulator
- doc                     // documentation, including a reading guide
- test                    // test files
  - riscv-tests           // snapshot of tests from the riscv/riscv-tests github repo
- os-boot                 // information and sample files for booting OS images


The files in the OCaml and C emulator directories implement ELF loading and the platform devices, define the physical memory map, and use command-line options to select implementation-specific ISA choices.


The files under handwritten_support provide library definitions for Coq, Isabelle and HOL4.

Building the model

Install Sail via Opam, or build Sail from source and have SAIL_DIR in your environment pointing to its top-level directory.

$ make

will build the 64-bit OCaml simulator in ocaml_emulator/riscv_ocaml_sim_RV64, the C simulator in c_emulator/riscv_sim_RV64, the Isabelle model in generated_definitions/isabelle/RV64/Riscv.thy, the Coq model in generated_definitions/coq/RV64/riscv.v, and the HOL4 model in generated_definitions/hol4/RV64/riscvScript.sml.

One can build either the RV32 or the RV64 model by specifying ARCH=RV32 or ARCH=RV64 on the make line, and using the matching target suffix. RV64 is built by default, but the RV32 model can be built using:

$ ARCH=RV32 make

which creates the 32-bit OCaml simulator in ocaml_emulator/riscv_ocaml_sim_RV32, and the C simulator in c_emulator/riscv_sim_RV32, and the prover models in the corresponding RV32 subdirectories.

The Makefile targets riscv_isa_build, riscv_coq_build, and riscv_hol_build invoke the respective prover to process the definitions. We have tested Isabelle 2018, Coq 8.8.1, and HOL4 Kananaskis-12. When building these targets, please make sure the corresponding prover libraries in the Sail directory ($SAIL_DIR/lib/$prover) are up-to-date and built, e.g. by running make in those directories.

Executing test binaries

The C and OCaml simulators can be used to execute small test binaries. The OCaml simulator depends on the Device Tree Compiler package, which can be installed in Ubuntu with:

$ sudo apt-get install device-tree-compiler

Then, you can run test binaries:

$ ./ocaml_emulator/riscv_ocaml_sim_<arch>  <elf-file>
$ ./c_emulator/riscv_sim_<arch> <elf-file>

A suite of RV32 and RV64 test programs derived from the riscv-tests test-suite is included under test/riscv-tests/. The test-suite can be run using test/

Configuring platform options

Some information on additional configuration options for each simulator is available from ./ocaml_emulator/riscv_ocaml_sim_<arch> -h and ./c_emulator/riscv_sim_<arch> -h.

Some useful options are: configuring whether misaligned accesses trap (--enable-misaligned for C and -enable-misaligned for OCaml), and whether page-table walks update PTE bits (--enable-dirty-update for C and -enable-dirty-update for OCaml).

Booting OS images

For booting operating system images, see the information under the os-boot/ subdirectory.


This software was developed by SRI International and the University of Cambridge Computer Laboratory (Department of Computer Science and Technology) under DARPA/AFRL contract FA8650-18-C-7809 ("CIFV"), and under DARPA contract HR0011-18-C-0016 ("ECATS") as part of the DARPA SSITH research programme. This software was developed within the Rigorous Engineering of Mainstream Systems (REMS) project, partly funded by EPSRC grant EP/K008528/1, at the Universities of Cambridge and Edinburgh.

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