94 Syntax of the language
The code of rz_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 rz_asm and
injected into a tiny binary with rz_bin.
You may like to use rz_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.
94.1 Preprocessor
94.1.1 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);
94.1.2 Includes
Use cat(1) or the preprocessor to concatenate multiple files to be compiled.
INCDIR@alias("/usr/include/rz-gg");
sys-osx.r@include(INCDIR);
94.1.3 Hashbang
eggs can use a hashbang to make them executable.
$ head -n1 hello.r
#!/usr/bin/rz-gg -X
$ ./hello.r
Hello World!
94.1.4 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/rz-gg -X
main();
...
main@global(128,64) {
...
94.1.5 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 ‘{ … }’
94.1.6 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
94.1.7 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
94.1.8 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);
}
94.1.9 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.
94.1.10 Core library
There’s a work-in-progress libc-like library written completely in r_egg
94.1.11 Variables
.arg
.arg0
.arg1
.arg2
.var0
.var2
.fix
.ret ; eax for x86, r0 for arm
.bp
.pc
.sp
Attention: All the numbers after .var and .arg mean the offset with the
top of stack, not variable symbols.
94.1.12 Arrays
Supported as raw pointers. TODO: enhance this feature
94.1.13 Tracing
Sometimes r_egg programs will break or just not work as expected. Use the
‘trace’ architecture to get a arch-backend call trace:
$ rz-gg -a trace -s yourprogram.r
94.1.14 Pointers
TODO: Theoretically ‘*’ is used to get contents of a memory pointer.
94.1.15 Virtual registers
TODO: a0, a1, a2, a3, sp, fp, bp, pc
94.1.16 Math operations
rz-gg supports local variables assignment by math operating, including
the following operators:
+ - * / & | ^
94.1.17 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);
}
$ rz-gg -F -o test test.r
$ ./test
$ echo $?
794.1.18 Traps
Each architecture have a different instruction to break the execution of
the program. RzEgg 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
94.1.19 Inline assembly
Lines prefixed with ‘:’ char are just inlined in the output assembly.
: jmp 0x8048400
: .byte 33,44
94.1.20 Labels
You can define labels using the : keyword like this:
:label_name:
/* loop forever */
goto(label_name)
94.1.21 Control flow
goto (addr) – branch execution
while (cond)
if (cond)
if (cond) { body } else { body }
break () – executes a trap instruction
94.1.22 Comments
Supported syntax for comments are:
/* multiline comment */'// single line comment# single line comment