badc (performance)

badc is a cross-platform optimizing C compiler, also usable as a Rust library. From any host it builds native executables, shared libraries and objects for five targets: macOS on ARM64, Linux on ARM64 and x86-64, and Windows on ARM64 and x86-64. It has its own preprocessor, assembler, linker, archiver and DWARF writer, an in-process JIT and an SSA interpreter. CI runs over 80 jobs and over 5,000 tests on every pull request and every push to master, and fuzzing jobs run daily.

• badc was bad when the project started, and the name stuck.
• --dump-ssa prints each function’s SSA IR and the register allocator’s placement of each value to stderr before lowering.

Contents

• Demos
• Lineage
• Documentation
• Disclaimer

Demos

demos/ builds each project below with badc and runs it as a smoke test. demos/README.md says what each one exercises.

• Language interpreters: Python 3.14 on all five targets, Lua, QuickJS, Tcl.
• Systems software: SQLite, curl, QEMU. QEMU is over a thousand units per target, linked by badc’s own linker. The badc-built qemu-system-aarch64 and qemu-system-x86_64 boot Linux through UEFI firmware to a shell under TCG.
• Toolchains: chibicc, TinyCC, and the nasm and yasm assemblers, each run against its own test suite.
• Firmware and kernels:
  • edk2: badc builds the OVMF and AAVMF UEFI firmware from source, and the CI boots run under that firmware.
  • efi_hello: a single-source EFI application; #pragma subsystem selects its PE subsystem.
  • kernel: a freestanding preemptive multitasking kernel for both architectures, with timer interrupts and context switches.
  • Linux: the Linux 7.2.9 kernel; see the kernel page.
• Cryptography and compression: TweetNaCl, Monocypher, BearSSL, miniz, bzip2, and OpenSSL with its make test.
• Graphics and math: stb, raylib with a Lode Runner game, Nuklear, kissfft, and the GUI demos: one windowed program per OS family, each cross-compiled to every target. Nuklear’s demo windows, rendered without a display, give the same frames under badc -O0, badc -O and the host compiler.
• Windows system code: the WDM kernel driver; SimpleVisor, an Intel VT-x hypervisor built as a native-subsystem driver; nt_hello, an IMAGE_SUBSYSTEM_NATIVE program that runs on ntdll alone; and nt_loader, which starts one through NtCreateUserProcess.
• Coroutines: libmill, libdill and coroutines, whose context switches run through inline asm.
• Editors and terminal tools: uemacs, MicroEMACS from Linus Torvalds’ tree; picocom, a serial terminal emulator, tested between two pseudo-terminals; GNU Screen, tested as both halves of its client/server pair; and Vim, tested in ex mode and with keystrokes at a pseudo-terminal.

Lineage

badc started as a Rust port of Robert Swierczek’s c4, a C compiler in four functions. The dialect diverged enough to get its own name, c5, hence the c5 module and the C5Error type. It has since moved from a stack IR through a three-operand IR to SSA with an optimizing backend.

c4.c is a test fixture, and badc compiles it:

badc -O -o c4 tests/fixtures/c/c4.c           # compile c4 to a native binary
./c4 tests/fixtures/c/c4_selfhost_hello.c     # c4 compiles and runs a program

c4 also runs itself. This runs the hello program under c4, under c4, under c4 compiled by badc’s JIT:

badc -O --jit tests/fixtures/c/c4.c tests/fixtures/c/c4.c tests/fixtures/c/c4.c \
    tests/fixtures/c/c4_selfhost_hello.c

Hello 123
exit(0) cycle = 11
exit(0) cycle = 37229
exit(0) cycle = 11152710

c4 accepts a subset of C. For example, it rejects a local declaration with an initializer.

Documentation

• What badc can do: a short survey of the features.
• Getting started: install, first run, flags, debugging, C as a script.
• Native compilation: targets, the instruction-set baseline (x86-64-v3, the Apple M1’s ARMv8.4-A), multiple translation units, the linker, headers and bindings, #pragma build flags, the JIT, optimizations.
• Diagnostics: every warning and error with its code and name, and the -W options and pragmas that select them.
• Standard conformance: implementation-defined choices, divergences from C17, and the C23, POSIX, GCC and MSVC extensions badc implements.
• The Linux kernel: what badc compiles, links and boots of the kernel, and how it is checked.
• --interp and --jit: running C without writing an image, and the interpreter’s pointer checks.
• Library and no_std: using badc from Rust.
• Testing: the suites, fixtures, snapshots, fuzzing, benchmarks and CI.
• Tools: the helper programs under tools/ and scripts/.
• Performance: CI’s benchmark results.
• Contributing: what a pull request needs to be merged.

Disclaimer

This is a personal educational and research project. Nobody sponsored or suggested it. I am not responsible for how you use it or for what follows from that use. See LICENSE for the exact terms.

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