BCause - B compiler for modern systems

BCause is a compiler for the B programming language, developed by Ken Thompson and Dennis Ritchie at Bell Labs in 1969, later getting replaced by C. BCause is written in C99 and relies on a minimal set of dependencies, namely libc and the GNU binutils.

This repository also includes a libb.a implementation, B's standard library. It requires zero dependencies, not even libc.

BCause is implemented as a small single-pass compiler in ~2500 lines of pure C99 code. Therefore, it features small compile times with a very low memory footprint.

This fork also contains a set of reading notes and source annotations for people who want to study BCause as a compact compiler/runtime specimen. If your goal is to understand the implementation, start with READING_ORDER.md.

Reading the implementation

BCause is small enough to read, but it is still easy to enter from the wrong end. The recommended route is:

1. READING_ORDER.md — linear reading order.
2. NOTES.md — high-level learning map.
3. src/README.md — source tree overview.
4. src/compiler/README.md — compiler overview.
5. src/libb/README.md — runtime overview.
6. docs/README.md — long-form documentation index.

The main deep-dive documents are:

• docs/compiler-pipeline.md — source to executable pipeline.
• docs/diagnostics-and-parser.md — character-level parser and diagnostics.
• docs/data-layout.md — B word, scalar/vector layout, strings, character packing.
• docs/expression-lowering.md — lvalue/rvalue and expression code generation.
• docs/statement-lowering.md — labels, jumps, and statement lowering.
• docs/abi-and-stack.md — System V AMD64 ABI and stack frame model.
• docs/libb-runtime.md — freestanding runtime, _start, syscalls, and standard functions.
• docs/known-limitations.md — current limitations and likely improvement points.

The source itself also contains explanatory comments. They are meant for readers already comfortable with C and Unix, so the comments focus on BCause-specific control flow, layout, ownership, ABI boundaries, and historical B behavior rather than basic C syntax.

Current Status

• global variables
• functions
• auto & extrn variables
• control flow statements
• expressions
• libb.a standard library
• optimization
• nicer error messages

Compatibility

Due to BCause's simplicity, only gnu-linux-x86_64-systems are supported.

• If your system can run GNU-make, GNU-ld and GNU-as, BCause itself should be able to work.
• Because of the reliance on system-calls libb.a has to be implemented for each system separately.

Note Feel free to submit pull requests to provide more OS support and fix bugs.

Installation

To install BCause, first clone this repository:

$ git clone https://github.com/spydr06/bcause.git
$ cd ./bcause

Then, build the project:

$ make

To install BCause on your computer globally, use:

# make install

Warning this requires root privileges and modifies system files

Usage

To compile a B source file (.b), use:

$ bcause <your file>

To get help, type:

$ bcause --help

Testing

The tests/ directory contains numerous compiler tests. Please update these tests when adding new features. Tests are based on googletest and require cmake to be run:

$ make test

Licensing

BCause is licensed under the MIT License. See LICENSE in this repository for further information.

References

• Bell Labs User's Reference to B by Ken Thompson (Jan. 7, 1972)

• Wikipedia entry: B (programming language)