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cproc is a C11 compiler using QBE as a backend. It is released under the ISC license.

Some C23 features and GNU C extensions are also implemented.

There is still much to do, but it currently implements most of the language and is capable of building software including itself, mcpp, gcc 4.7, binutils, and more.

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


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 yet 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


Run ./configure to create a config.h and 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 with the appropriate CC, CFLAGS and LDFLAGS.

Once this is done, you can build with



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).
  • Variable-length arrays (#1).
  • volatile-qualified types (#7).
  • long double type (#3).
  • Inline assembly (#5).
  • Preprocessor (#6).
  • Generation of position independent code (i.e. shared libraries, modules, PIEs).

Mailing list

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

Issue tracker

Please report any issues to ~mcf/


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