(mirrored on GitHub and Codeberg)

cproc is a C compiler using QBE as a backend, released under the ISC license. It implements most of C11 as well as many C23 features. Additionally, it implements a few GNU C extensions.

It is currently able to build a lot of C software, though occasionally requires small patches to fix C conformance issues.

It was inspired by several other small C compilers including 8cc, c, lacc, and scc.

Goals

cproc aims to closely follow the C standard, but also to be a practical tool able compile many real-world software packages. Sometimes, these goals can be at ends with each other, since there is a lot of non-conforming C code out there.

The main philosophy regarding C extensions is this:

• If the code could be made portable with some small tweaks that do not affect performance or readability, then the code should be patched accordingly.
• Only when an extension is widely used and cannot be easily transformed into a portable equivalent is it considered for implementation. Ideally, it should also be accompanied with a proposal to WG14 so that its semantics are well specified.

By following these guidelines, hopefully cproc can help shrink the gap between what's required to implement the C specification and what's required to compile real C software.

cproc does not implement multiple versions of C. Instead, code affected by breaking changes in new C versions (such as the new keywords introduced in C23) must be updated or patched to be compatible with the new version.

Requirements

The compiler itself is written in standard C99 and can be built with any conforming C99 compiler.

The POSIX driver depends on POSIX.1-2008 interfaces, and the Makefile requires a POSIX-compatible make(1).

At runtime, you will need QBE, an assembler, and a linker for the target system. Since the preprocessor is not fully implemented, an external one is currently required as well.

Supported targets

All architectures supported by QBE should work (currently x86_64, aarch64, and riscv64).

The following targets are tested by the continuous build and known to bootstrap and pass all tests:

• x86_64-linux-musl
• x86_64-linux-gnu
• x86_64-freebsd
• aarch64-linux-musl
• aarch64-linux-gnu
• riscv64-linux-gnu

Building

Run ./configure to create a config.h and config.mk appropriate for your system. If your system is not supported by the configure script, you can create these files manually. config.h should define several string arrays (static char *[]):

• startfiles: Objects to pass to the linker at the beginning of the link command.
• endfiles: Objects to pass to the linker at the end of the link command (including libc).
• preprocesscmd: The preprocessor command, and any necessary flags for the target system.
• codegencmd: The QBE command, and possibly explicit target flags.
• assemblecmd: The assembler command.
• linkcmd: The linker command.

You may also want to customize your environment or config.mk with the appropriate CC, CFLAGS and LDFLAGS.

Once this is done, you can build with

make

Bootstrap

The Makefile includes several other targets that can be used for bootstrapping. These targets require the ability to run the tools specified in config.h.

• stage2: Build the compiler with the initial (stage1) output.
• stage3: Build the compiler with the stage2 output.
• bootstrap: Build the stage2 and stage3 compilers, and verify that they are byte-wise identical.

What's missing

• Digraph sequences (6.4.6p3, will not be implemented).
• volatile-qualified types (#7, requires qbe support).
• long double type (#3, requires qbe support).
• The preprocessor is not fully implemented (#6).
• Generation of position independent code (i.e. shared libraries, modules, PIEs).

C11

• Complex types (optional).
• Atomic types (optional).

C23

See C23 for a detailed breakdown of the language-level changes from C11 to C23 as well as their current status. Notably, the following are not yet implemented:

• constexpr
• auto
• #embed

GNU C extensions

• Inline assembly (#5, requires qbe support).
• Statement expressions (#20, unlikely to be implemented without specification and WG14 acceptance).

Mailing list

There is a mailing list at ~mcf/cproc@lists.sr.ht. Feel free to use it for general discussion, questions, patches, or bug reports (if you don't have an sr.ht account).

If you don't hear a response, please don't hesitate to bump your thread.

Issue tracker

Please report any issues to ~mcf/cproc@todo.sr.ht.

Contributing

Patches are greatly appreciated. Send them to the mailing list (preferred), or as pull-requests on the Codeberg mirror.