The Cog VM source tree
This is the README for the Cog Git source tree: https://github.com/OpenSmalltalk/opensmalltalk-vm
Builds are tested automatically on each commit, for Windows, macOS, and Linux. Windows and Linux also have 32-bit targets. Squeak and Pharo VMs are built with and without JIT, with and without Spur, and with and without Sista, as available per platform. All build artifacts remain accessible for 90 days for each workflow run; the latest artifacts are uploaded to a dedicated release tag (e.g., "latest-build"), overwritten with each successful run. If you wish to commit without triggering a build, for example if you were to only edit this documentation, then if you add [ci skip] somewhere in your commit message, no workflow run will be started for that commit.
Important notice for Developers:
We rely on source file substitutions in the src tree, specifically,
any sq*SCCSVersion.h files anywhere in the tree are processed to replace
$URL$ with the current revision (defined as the
timestamp %Y%m%d%H%M of the latest commit), the human readable date of that
commit, and the url of the origin repository these sources were cloned from.
The first time you clone this repository, you must therefore run this command:
This will install filters, post-commit, and post-merge hooks to update the sq*SCCSVersion.h files anytime you commit or merge.
For easier use, we include the scripts/gitci and scripts/gitciplugins scripts to
commit changes to this branch and changes to the Cross and win32 plugins (which
are shared with the old Squeak interpreter trunk). If you decide not to use
these scripts for checking in sources, you should also run the
updateSCCSVersions script anytime you decide to use
git-checkout to make sure the stamps are updated correctly. Failing to do so
will result in incorrect version stamps in your compiled VMs.
- VM source directories
- Platform build directories
- Other directories
First, opensmalltalk-vm (a.k.a. the Cog VM) is the virtual machine beneath the Cuis, Pharo and Squeak Smalltalk dialects. For issues related to these systems that are unrelated to the VM itself, please use their forums:
Second, the core VM, which comprises the execution engine and garbage collector,
and the core plugins, is developed in Smalltalk, using the VM Simulator. This
repository contains the code generated by the Simulator, and the platform support
code for the entire VM, its CI infrastructure and so on. The core VM should
not be developed by editing the generated code. The core VM should be
developed using Smalltalk. The source code repository for the VM is
You can find scripts to build a Smalltalk image in which to do core VM development in the image directory in this repository. You can read about the Simulator here:
- https://hal.archives-ouvertes.fr/hal-01883380/document Please look at the wiki on this site for a description of on-going projects.
Cog is an evolution of the Squeak Back-to-the-future Smalltalk virtual machine that provides a number of different Smalltalk virtual machines. The VMs are developed in Smalltalk, using all the dynamic and reflective facilities of the Squeak/Pharo Smalltalk system. As such, developing in Cog is a delight. The Smalltalk framework comprising the various Cog VMs is translated into C by its Slang component to produce VM source that is combined with platform-specific support sources and compiled via a C compiler to obtain a fast production VM. This directory tree includes the output of Slang for various configurations of "Cog VM" and the associated platform support code, plus build directories that can be used to produce production VMs.
This directory tree also includes an instance of the Smalltalk Cog development system, suitable for developing the VM in Smalltalk, and for generating new VM sources.
The "Cog VM" comes in a bewildering variety of forms. The first distinction is between Stack, Cog and Sista VMs. Stack VMs are those with context-to-stack mapping that optimise message sending by keeping method activations on a stack instead of in contexts. These are pure interpreters but are significantly faster than the standard context-based Interpreter VM. Cog VMs add a JIT to the mix, compiling methods used more than once to machine code on the fly. Sista VMs, as yet unrealised and in development, add support for adaptive optimization that does speculative inlining at the bytecode-to-bytecode level.
Another distinction is between "v3" VMs and Spur VMs. "v3" is the original object representation for Squeak as described in the back-to-the-future paper. Spur, as described on the www.mirandabanda.org blog, is a faster object representation which uses generation scavenging, lazy forwarding for fast become, a single object header format common to 32 and 64 bit versions, and a segmented heap that can grow and shrink, releasing memory back to the host OS. Squeak 5.0, Cuis 5 and Pharo 5 and subsequent releases use Spur.
Another distinction is between normal single-threaded VMs that schedule "green" Smalltalk light-weight processes above a single-threaded VM, and multi-threaded VMs that share the VM between any number of native threads such that only one native thread owns the VM at any one time, switching between threads on FFI calls and callbacks or on Smalltalk process switches when Smalltalk processes are owned by threads. This architecture offers non-blocking FFI calls and interoperability with multiple native threads, but does /not/ provide true concurrency. This multi-threaded support is as yet experimental.
VM source directories
The Slang output of the various VMs are kept in "vm source" directories. These C sources define the core VM (the Smalltalk execution engine and the memory manager), and a substantial set of "plugins" that provide interfaces to various external facilities via Smalltalk primitive methods. Each vm source directory is specific to a particular VM, be it Squeak Cog Spur, or V3 Stack, etc. The plugins can be shared between VMs, choosing the set of plugins to include in a VM at build time (see plugins.int & plugins.ext in build directories).
The VM source are in directories such as
src/v3.sista - Smalltalk Sista V3 src/spur32.sista - Smalltalk Sista Spur src/spur32.cog - Smalltalk Cog Spur src/spur64.cog - Smalltalk Cog Spur 64-bit src/spur32.stack - Smalltalk Stack Spur src/spur64.stack - Smalltalk Stack Spur 64-bit src/v3.cog - Smalltalk Cog V3 src/v3.stack - Smalltalk Stack V3
All plugins are in the directory
These contain many, but not all, of the plugins available for the VM. Others can be found in Cog, or in various Monticello packages in various repositories.
Each vm source directory contains several files, a subset of the following:
cogit.c - the JIT; a Cogit cooperates with a CoInterpreter. This simply includes a processor-specific JIT file cogitIA32.c et al - relevant processor-specific JIT, selected by cogit.c cogit.h - the Cogit's API, as used by the CoInterpreter cogmethod.h - the structure of a CogMethod, the output of the Cogit cointerp.c - the CoInterpreter's source file cointerp.h - the API of the CoInterpreter, as used by the Cogit cointerpmt.c - the multi-threaded CoInterpreterMT's source file cointerpmt.h - the API of the CoInterpreterMT, as used by the Cogit gcc3x-cointerp.c - cointerp.c massaged to interpret faster if using gcc gcc3x-cointerpmt.c - ditto for cointerpmt.c gcc3x-interp.c - ditto for interp.c interp.c - the StackInterpreter's source file interp.h - defines for the VM configuration, word size, etc vmCallback.h - the structure of the VM's VMCallbackContext
Platform build directories
The current "official" build directories are of the form building/OS_WordSize_Processor, and include
building/linux32x86 - uses autoconf, gcc and make building/macos32x86 - 32-bit Mac OS X using clang and gmake building/macos64x64 - 64-bit Mac OS X using clang and gmake building/win32x86 - uses cygwin, gcc and gmake
More can be added as required. In each there is a HowToBuild that describes the necessary steps to compile a VM.
Within each building/OS_WordSize_Processor directory are a set of build directories for specific configurations of Cog, and for support code and makefiles. For example, there exist
building/macos32x86/squeak.cog.spur - A Cog JIT VM with Squeak branding, using the Spur memory manager. building/macos32x86/squeak.stack.spur - A Stack interpreter VM with Squeak branding, and the Spur memory manager. building/macos32x86/squeak.cog.v3 - A Cog JIT VM with Squeak branding, using the old Squeak memory manager. building/macos32x86/pharo.cog.spur - A Cog JIT VM with Pharo branding and plugins (not yet implemented) using the Spur memory manager.
building/macos64x64/bochsx86 - Support libraries for the BochsIA32Plugin which is used to develop Cog itself. building/macos64x64/bochsx64 - Support libraries for the BochsX64Plugin which is used to develop Cog itself. building/macos64x64/gdbarm32 - Support libraries for the GdbARMPlugin which is used to develop Cog itself. building/macos64x64/gdbarm64 - Support libraries for the GdbARMv8Plugin which is used to develop Cog itself.
and the intention is to add such directories to contain e.g. support code for the Pharo Cairo and Freetype plugins, and anything else needed. By placing support directories in each build directory they can be shared between various branded VM builds, avoiding duplication.
building/macos32x86/common - Gnu Makefiles for building the various branded VMs building/macos64x64/common - Gnu Makefiles for building the various branded VMs building/win32x86/common - Gnu Makefiles for building the various branded VMs building/win64x64/common - Gnu Makefiles for building the various branded VMs
And the intention is to add building/linuxNN????/common as soon as possible to use Gnu Makefiles to build all VMs on all platforms.
The scripts directory contains various scripts for validating and checking-in generated sources, packaging builds into installable artifacts (tar, msi, zip), and so on. The linux builds and the packaging scripts produce outputs in the products directory tree. The packaging scripts may choose to include Smalltalk source files included in the sources directory.
The platforms directory contains the associated platform-specific files that combine with the Slang-generated source to produce complete VMs. The structure is
platforms/Cross/vm platforms/Cross/plugins platforms/iOS/vm platforms/iOS/plugins platforms/unix/vm* platforms/unix/plugins platforms/win32/vm platforms/win32/plugins
Each vm directory contains support for the core VM. Each plugin directory contains run-time and build-time support for various plugins.
The processors directory contains the source for various processor simulators. The JIT is developed in Smalltalk by using one of these processor simulators to execute the code the JIT produces. Currently x86 & x86-64 are derived from Bochs, and ARMv6/v7 & ARMv8 are derived from gdb.
Finally the image directory contains scripts that will build a "VMMaker" image, a Squeak Smalltalk image containing all the packages that comprise the Cog system, suitable for developing the VM and for generating (or updating) the sources in the vm source directories. There is also a script for generating a 64-bit Spur image from a 32-bit Spur image.
Eliot Miranda April 2021