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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.
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);`
Use `cat(1)` or the preprocessor to concatenate multiple files to be compiled.
` INCDIR@alias("/usr/include/ragg2");`
` sys-osx.r@include(INCDIR);`
eggs can use a hashbang to make them executable.
`$ head -n1 hello.r`
` #!/usr/bin/ragg2 -X`
` $ ./hello.r`
` Hello World!`
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) {`
` ...`
You may like to split up your code into several code blocks. Those blocks
are bound to a label followed by root brackets '{ ... }'
`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
`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
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);`
` }`
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.
There's a work-in-progress libc-like library written completely in r\_egg
`.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.
Supported as raw pointers. TODO: enhance this feature
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`
TODO: Theorically '\*' is used to get contents of a memory pointer.
TODO: a0, a1, a2, a3, sp, fp, bp, pc
Ragg2 supports local variables assignment by math operating, including
the following operators:
`+` `-` `*` `/` `&` `|` `^`
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)`
` if (cond) { body } else { body }`
` break ()` -- executes a trap instruction
### Comments
Supported syntax for comments are:
` /* multiline comment */'`
` // single line comment`
` # single line comment`