radare2/libr/egg

r_egg
===== --pancake

This is a rewrite of rarc2, a relocatable code compiler for radare.

Syntax of the language
======================
The code of r_egg is compiled as in a flow. It is a one-pass compiler;
this means that you have to define the proper stackframe size at the
beginning of the function, and you have to define the functions in
order to avoid getting compilation errors.

The compiler generates assembly code for x86-{32,64} and arm. But it aims
to support more platforms. This code is the compiled with r_asm and
injected into a tiny binary with r_bin.

You may like to use r_egg to create standalone binaries, position-
independent raw eggs to be injected on running processes or to patch
on-disk binaries.

The generated code is not yet optimized, but it's safe to be executed
at any place in the code.

Preprocessor
------------
There's no standard preprocessor integrated with it. But if you feel
the need to use one you may use cpp or spp*.

  * hg clone http://hg.youterm.com/spp

Aliases
-------
Sometimes you just need to replace at compile time a single entity on
multiple places. Aliases are translated into 'equ' statements in assembly
language. This is just an assembler-level keyword redefinition.

  AF_INET@alias(2);
  printf@alias(0x8053940);

Includes
--------
Use cat(1) or the preprocessor to concatenate multiple files to be compiled.
It's not a task of a compiler to look for external sources, so it's a
delegated task right now.. but we will probably add native support for
spp (merge into)

TODO: this is not yet implemented

  INCDIR@alias("/usr/include/ragg2");
  sys-osx.r@include(INCDIR);

Hashbang
--------
eggs can use a hashbang to make them executable.

  $ head -n1 hello.r
  #!/usr/bin/ragg2 -X
  $ ./hello.r
  Hello World!

Main
----
The execution of the code is done as in a flow. The first function to be
defined will be the first one to be executed. If you want to run main()
just do like this:

  #!/usr/bin/ragg2 -X
  main();
  ...
  main@global(128,64) {
    ...

Function definition
-------------------
You may like to split up your code into several code blocks. Those blocks
are bound to a label followed by root brackets '{ ... }'

Function signatures
-------------------
name@type(stackframesize,staticframesize) { body }

name : name of the function to define
type : see function types below
stackframesize : get space from stack to store local variables
staticframesize : get space from stack to store static variables (strings)
body : code of the function

Function types
--------------
  alias     ; Used to create aliases
  data      ; the body of the block is defined in .data
  inline    ; the function body is inlined when called
  global    ; make the symbol global
  fastcall  ; function that is called using the fast calling convention
  syscall   ; define syscall calling convention signature

Syscalls
--------
r_egg offers a syntax sugar for defining syscalls. The syntax is like this:

  exit@syscall(1);
  @syscall() {
    : mov eax, `.arg`
    : int 0x80
  }
  main@global() {
    exit (0);
  }

Libraries
---------
At the moment there is no support for linking r_egg programs to system
libraries. but if you inject the code into a program (disk/memory) you
can define the address of each function using the @alias syntax.

Core library
------------
There's a work-in-progress libc-like library written completely in r_egg

Variables
---------
.arg
.arg0
.arg1
.arg2
.var0
.var2
.fix
.ret    ; eax for x86, r0 for arm
.bp
.pc
.sp

Arrays
------
Supported as raw pointers. TODO: enhance this feature

Tracing
-------
Sometimes r_egg programs will break or just not work as expected. Use the
'trace' architecture to get a arch-backend call trace:

  $ ragg2 -a trace -s yourprogram.r

Pointers
--------
TODO: Theorically '*' is used to get contents of a memory pointer.

Virtual registers
-----------------
TODO: a0, a1, a2, a3, sp, fp, bp, pc

Return values
-------------
The return value is stored in the a0 register, this register is set when
calling a function or when typing a variable name without assignment.

   $ cat test.r
   add@global(4) {
      .var0 = .arg0 + .arg1;
      .var0;
   }
   main@global() {
      add (3,4);
   }

   $ ragg2 -F -o test test.r
   $ ./test
   $ echo $?
   7

Traps
-----
Each architecture have a different instruction to break the execution of
the program. REgg language captures calls to 'break()' to run the emit_trap
callback of the selected arch. The 

  break(); --> compiles into 'int3' on x86
  break; --> compiles into 'int3' on x86

Inline assembly
---------------
Lines prefixed with ':' char are just inlined in the output assembly.

   : jmp 0x8048400
   : .byte 33,44

Labels
------
You can define labels using the ':' keyword like this:

   :label_name:
   /* loop forever */
   goto(label_name)

Control flow
------------
  goto (addr) -- branch execution
  while (cond)
  if (cond)
  break () -- executes a trap instruction

Comments
--------
Supported syntax for comments are: 

  /* multiline comment */' 
  // single line comment
  # single line comment