cmm

Introduction

cmm (C minus minus) is a compiler which compiles the source code written in C-- language(which is a subset of C) into aarch64 assembly code. It's a project of the introductory compiler course in NTU.

Informal Specification of C--

C-- is based on ANSI C standard, thus only the differences are listed below.

Types

C-- only support five types, which are :

• int - signed integer - 4 bytes
• float - single percision floating pointer number - 4 bytes
• string literal - ascii string terminated with NULL byte, 1 byte for each character (Not declarable since it's a literal, should only be used with write(), which will mention later)
• int [] - address of an int array (only for function parameter) - 8 bytes
• float [] - address of an float array (only for function parameter) - 8 bytes

Operators

Only support the following operators: +, -, *, /, !, &&, ||, [](array subscription), ()(function call)

Syntax

• Functions without arguments should keep the parameter list empty instead of placing void.
• Does not support any type qualifier.
• Does not support assignment expression as rvalue.
• Entry point is MAIN instead of main.
• Function declaration and definition should not be seperated.
• All declarations should be placed in the front of the block.
• Does not support array initialization.
• No explicit type conversion, but implicity conversion between int and float is allowed.
• Max dimension of array is 10.
• Only support following control structures : for, while, if, else.

IO functions

There are five functions provided for IO operations:

• void write(int) print the argument (int) to the standard output.
• void write(float) print the argument (float) to the standard output.
• void write(string literal) print the argument (string literal) to the standard output.
• int read() read and return an integer value from standard inupt.
• float fread() read and return a floating point value from standard input.

Application Binary Interface

The cmm ABI is designed roughly based on the Aarch64 ABI, with some slightly diffences:

• Parameter passing using stack instead of register, only write() will use s0, x0, w0.
• Compiler has implement the caller/callee register convention.

Stack frame layout

|  ...                |
|---------------------|
|  old frame pointer  | <- old x29
|  local variables    |
|  callee saved regs  |
|  caller saved regs  |
|  function args      |
|  return address     |
|---------------------|
|  old frame pointer  | <- x29
|  ...                |

Build

Run

$ make

Usage

Run

$ ./parser input_file

The output file we be named output.s, which contains the aarch64 assembly.

output.s isn't self contained, it has to be compiled with main.S, which is a wrapper file provding IO rountines and entry loading for the compiled file.

So, use

$ aarch64-linux-gnu-gcc -static main.S

to compile the program, it will pulled in output.s and produce an aarch64 binary, then you may test the static binary with qemu-aarch64.