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AMaCC = Arguably Minimalist Arm C Compiler

Introduction

AMaCC is built from scratch, targeted at 32-bit ARM architecture. It is a considerably stripped down version of C and it is meant as pedagogical tool for learning about compilers, linkers, and loaders.

There are 2 execution modes AMaCC implements:

  • Just-in-Time compiler (JITC) for ARM backend
  • Generate valid GNU/Linux executables with Executable and Linkable Format (ELF)

It is worth mentioning that AMaCC is designed to compile the minimal subset of C required to self-host with the above execution modes. For example, global variables and, in particular, global arrays are there.

Intermediate code generation is integrated into the parsing since it is generating code for a stack-based machine and that also follows the sequence of actions performed when parsing.

It mixes classical recursive descent and operator precedence parser. An operator precedence parser is actually quite a bit faster than recursive descent parser (RDP) for expressions when operator precedence is defined using grammar productions that would otherwise get turned into methods.

Compatibility

AMaCC is capable of compiling C source files written in the following syntax:

  • data types: char, int, struct, and pointer
  • condition statements: if, while, for, switch, case, break, return, and general expressions
  • compound assignments: +=, -=, *=, /=, %=
  • global/local variable initializations for supported data types
    • e.g. int i = [expr]
    • New variables are allowed to be declared within functions anywhere.

The architecture support targets armv7hf with Linux ABI, verified on Raspberry Pi 2/3 with GNU/Linux.

Prerequisites

  • Code generator in AMaCC relies on several GNU/Linux behaviors, and it is necessary to have ARM/Linux installed in your build environment.

  • Install GNU Toolchain for the A-profile Architecture

    • Select arm-linux-none-gnueabihf (AArch32 target with hard float)
  • Install QEMU for ARM user emulation

sudo apt-get install qemu-user

Running AMaCC

Run make check and you should see this:

[ C to IR translation          ] Passed
[ JIT compilation + execution  ] Passed
[ ELF generation               ] Passed
[ nested/self compilation      ] Passed
[ Compatibility with GCC/Arm   ] ........................................
----------------------------------------------------------------------
Ran 48 tests in 7.354s

OK

Check the messages generated by make help to learn more.

Benchmark

AMaCC is able to generate machine code really fast and provides 70% of the performance of gcc -O0.

Test environment:

  • Raspberry Pi 3B (SoC: bcm2837, ARMv8-A architecture)
  • Raspbian GNU/Linux, kernel 4.14.98-v7+ (armv7l userland)

Input source file: amacc.c

comiler driver binary size (KiB) compile time (s)
gcc with -O0 -ldl (compile+link) 55 1.3007
gcc with -O0 -c (compile only) 53 1.1686
AMaCC 93 0.0373

Internals

Check Intermediate Representation (IR) for AMaCC Compilation.

Acknowledgements

AMaCC is based on the infrastructure of c4.

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