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Documentation Updates: reorder README and combine with STATUS.md #602

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193 changes: 109 additions & 84 deletions README.md
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Expand Up @@ -2,31 +2,19 @@ RISCV Sail Model
================

This repository contains a formal specification of the RISC-V architecture, written in
[Sail](https://github.com/rems-project/sail). It has been adopted by the RISC-V Foundation. As of 2021-08-24, the repo has been moved from <https://github.com/rems-project/sail-riscv> to <https://github.com/riscv/sail-riscv>.
[Sail](https://github.com/rems-project/sail). It has been adopted by the RISC-V Foundation.

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](doc/Status.md).
A [reading guide](doc/ReadingGuide.md) to the model is provided in the
[doc/](doc/) subdirectory, along with a guide on [how to
extend](doc/ExtendingGuide.md) the model.


Latex or AsciiDoc definitions can be generated from the model that are suitable
for inclusion in reference documentation. Drafts of the RISC-V
[unprivileged](https://github.com/rems-project/riscv-isa-manual/blob/sail/release/riscv-spec-sail-draft.pdf)
and [privileged](https://github.com/rems-project/riscv-isa-manual/blob/sail/release/riscv-privileged-sail-draft.pdf)
specifications that include the Sail formal definitions are available
in the sail branch of this [risc-v-isa-manual repository](https://github.com/rems-project/riscv-isa-manual/tree/sail).
The process to perform this inclusion is explained [here](https://github.com/rems-project/riscv-isa-manual/blob/sail/README.SAIL).
Latex or AsciiDoc definitions can be generated from the model that are suitable for inclusion in reference documentation.
There is also the newer [Sail AsciiDoctor documentation support for RISC-V](https://github.com/Alasdair/asciidoctor-sail/blob/master/doc/built/sail_to_asciidoc.pdf).

This is one of [several formal models](https://github.com/riscv/ISA_Formal_Spec_Public_Review/blob/master/comparison_table.md) that were compared within the 2019
[RISC-V ISA Formal Spec Public Review](https://github.com/riscv/ISA_Formal_Spec_Public_Review).


What is Sail?
-------------
Expand All @@ -51,12 +39,118 @@ permission), RISC-V, CHERI-RISC-V, CHERIoT, MIPS, and CHERI-MIPS; all these are
enough to boot various operating systems. There are also Sail models
for smaller fragments of IBM POWER and x86, including a version of the ACL2 x86 model automatically translated from that.

Getting started
---------------

### Building the model

Install [Sail](https://github.com/rems-project/sail/). On Linux you can download a [binary release](https://github.com/rems-project/sail/releases) (strongly recommended), or you can install from source [using opam](https://github.com/rems-project/sail/blob/sail2/INSTALL.md). Then:

```
$ make
```

will build the simulator in `c_emulator/riscv_sim_RV64`.

If you get an error message saying `sail: unknown option '--require-version'.` it's because your Sail compiler is too old. You need version 0.18 or later.

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 simulator in `c_emulator/riscv_sim_RV32`.

The Makefile targets `riscv_isa_build`, `riscv_coq_build`, and
`riscv_hol_build` invoke the respective prover to process the
definitions and produce the Isabelle model in
`generated_definitions/isabelle/RV64/Riscv.thy`, the Coq model in
`generated_definitions/coq/RV64/riscv.v`, or the HOL4 model in
`generated_definitions/hol4/RV64/riscvScript.sml` respectively.
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 simulator can be used to execute small test binaries.

```
$ ./c_emulator/riscv_sim_<arch> <elf-file>
```

A suite of RV32 and RV64 test programs derived from the
[`riscv-tests`](https://github.com/riscv/riscv-tests) test-suite is
included under [test/riscv-tests/](test/riscv-tests/). The test-suite
can be run using `test/run_tests.sh`.

### Configuring platform options

Information on configuration options for the simulator is available from
`./c_emulator/riscv_sim_<arch> -h`.

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

### Booting OS images

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

### Using development versions of Sail

Rarely, the release version of Sail may not meet your needs. This could happen if you need a bug fix or new feature not yet in the released Sail version, or you are actively working on Sail. In this case you can tell the `sail-riscv` `Makefile` to use a local copy of Sail by setting `SAIL_DIR` to the root of a checkout of the Sail repo when you invoke `make`. Alternatively, you can use `opam pin` to install Sail from a local checkout of the Sail repo as described in the Sail installation instructions.

Supported RISC-V ISA features
-----------------------------
#### The Sail specification currently captures the following ISA extensions and features:

- RV32I and RV64I base ISAs, v2.1
- Zifencei extension for instruction-fetch fence, v2.0
- Zicsr extension for CSR instructions, v2.0
- Zicntr and Zihpm extensions for counters, v2.0
- Zicond extension for integer conditional operations, v1.0
- Zicbom and Zicboz extensions for cache-block management (Zicbop not currently supported), v1.0
- M extension for integer multiplication and division, v2.0
- Zmmul extension for integer multiplication only, v1.0
- A extension for atomic instructions, v2.1
- Zalrsc extension for load-reserved and store-conditional operations, v1.0
- Zaamo extension for atomic memory operations, v1.0
- Zabha extension for byte and halfword atomic memory operations, v1.0
- F and D extensions for single and double-precision floating-point, v2.2
- Zfh extension half-precision floating-point, v1.0
- Zfa extension for additional floating-point instructions, v1.0
- Zfinx, Zdinx, and Zhinx extensions for floating-point in integer registers, v1.0
- C extension for compressed instructions, v2.0
- Zca, Zcf, Zcd, and Zcb extensions for code size reduction, v1.0
- B (Zba, Zbb, Zbs) and Zbc extensions for bit manipulation, v1.0
- Zbkb, Zbkc, and Zbkx extensions for bit manipulation for cryptography, v1.0
- Zkn (Zknd, Zkne, Zknh) and Zks (Zksed, Zksh) extensions for scalar cryptography, v1.0.1
- Zkr extension for entropy source, v1.0
- V extension for vector operations, v1.0
- Machine, Supervisor, and User modes
- Svinval extension for fine-grained address-translation cache invalidation, v1.0
- Sv32, Sv39, and Sv48 page-based virtual-memory systems
- Physical Memory Protection (PMP)

#### The following features are not currently supported:
- The Hypervisor Extension.
- RV32E and RV64E base ISAs
- Mutable XLEN (UXLEN/SXLEN always equal MXLEN)
- Big endian
- Physical Memory Attributes (PMAs)

Example RISC-V instruction specifications
----------------------------------

These are verbatim excerpts from the model file containing the base instructions, [riscv_insts_base.sail](https://github.com/riscv/sail-riscv/blob/master/model/riscv_insts_base.sail), with a few comments added.
These are verbatim excerpts from the model file containing the base instructions, [riscv_insts_base.sail](model/riscv_insts_base.sail), with a few comments added.

### ITYPE (or ADDI)
~~~~~
Expand Down Expand Up @@ -251,75 +345,6 @@ sail-riscv
- os-boot // information and sample files for booting OS images
```

Getting started
---------------

### Building the model

Install [Sail](https://github.com/rems-project/sail/). On Linux you can download a [binary release](https://github.com/rems-project/sail/releases) (strongly recommended), or you can install from source [using opam](https://github.com/rems-project/sail/blob/sail2/INSTALL.md). Then:

```
$ make
```

will build the simulator in `c_emulator/riscv_sim_RV64`.

If you get an error message saying `sail: unknown option '--require-version'.` it's because your Sail compiler is too old. You need version 0.18 or later.

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 simulator in `c_emulator/riscv_sim_RV32`.

The Makefile targets `riscv_isa_build`, `riscv_coq_build`, and
`riscv_hol_build` invoke the respective prover to process the
definitions and produce the Isabelle model in
`generated_definitions/isabelle/RV64/Riscv.thy`, the Coq model in
`generated_definitions/coq/RV64/riscv.v`, or the HOL4 model in
`generated_definitions/hol4/RV64/riscvScript.sml` respectively.
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 simulator can be used to execute small test binaries.

```
$ ./c_emulator/riscv_sim_<arch> <elf-file>
```

A suite of RV32 and RV64 test programs derived from the
[`riscv-tests`](https://github.com/riscv/riscv-tests) test-suite is
included under [test/riscv-tests/](test/riscv-tests/). The test-suite
can be run using `test/run_tests.sh`.

### Configuring platform options

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

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

### Booting OS images

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

### Using development versions of Sail

Rarely, the version of Sail packaged in opam may not meet your needs. This could happen if you need a bug fix or new feature not yet in the released Sail version, or you are actively working on Sail. In this case you can tell the `sail-riscv` `Makefile` to use a local copy of Sail by setting `SAIL_DIR` to the root of a checkout of the Sail repo when you invoke `make`. Alternatively, you can use `opam pin` to install Sail from a local checkout of the Sail repo as described in the Sail installation instructions.

Licence
-------

Expand Down
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