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VIXL: Runtime Code Generation Library Version 1.0

Contents:

  • Requirements
  • Overview
  • Known limitations
  • Usage

Requirements

To build VIXL the following software is required:

  1. Python 2.7
  2. Scons 2.0
  3. GCC 4.4

A 64-bit host machine is required, implementing an LP64 data model. VIXL has only been tested using GCC on Ubuntu systems.

To run the linter stage of the tests, the following software is also required:

  1. Git
  2. Google's cpplint.py

Refer to the 'Usage' section for details.

Overview

VIXL is made of three components.

  1. A programmatic assembler to generate A64 code at runtime. The assembler abstracts some of the constraints of the A64 ISA, for example most instructions support any immediate.
  2. A disassembler which can print any instruction emitted by the assembler.
  3. A simulator which can simulate any instruction emitted by the assembler. The simulator allows generated code to be run on another architecture without the need for a full ISA model.

Known Limitations

VIXL was developed to target JavaScript engines so a number of features from A64 were deemed unnecessary:

  • No Advanced SIMD support.
  • Limited rounding mode support for floating point.
  • No support for synchronisation instructions.
  • Limited support for system instructions.
  • A few miscellaneous integer and floating point instructions are missing.

The VIXL simulator supports only those instructions that the VIXL assembler can generate.

Usage

Running all Tests

The helper script tools/presubmit.py will build and run every test that is provided with VIXL, in both release and debug mode. It is a useful script for verifying that all of VIXL's dependencies are in place and that VIXL is working as it should.

By default, the tools/presubmit.py script runs a linter to check that the source code conforms with the code style guide, and to detect several common errors that the compiler may not warn about. This is most useful for VIXL developers. The linter has the following dependencies:

  1. Git must be installed, and the VIXL project must be in a valid Git repository, such as one produced using git clone.
  2. cpplint.py, as provided by Google, must be available (and executable) on the PATH. Only revision 104 has been tested with VIXL.

It is possible to tell tools/presubmit.py to skip the linter stage by passing --nolint. This removes the dependency on cpplint.py and Git. The --nolint option is implied if the VIXL project is a snapshot (with no .git directory).

Building and Running Specific Tests

The helper script tools/test.py will build and run all the tests for the assembler and disassembler in release mode. Add --mode=debug to build and run in debug mode. The tests can be built separately using SCons: scons target=cctest.

Building and Running the Benchmarks

There are two very basic benchmarks provided with VIXL:

  1. bench_dataop, emitting adds
  2. bench_branch, emitting branches

To build one benchmark: scons target=bench_xxx, then run it as ./bench_xxx_sim <number of iterations>. The benchmarks do not report a figure; they should be timed using the time command.

Getting Started

A short introduction to using VIXL can be found at doc/getting-started.md. Example source code is provided in the examples directory. Build this using scons target=examples from the root directory.