Fiddle: A Tool For Studying Small Compiled rograms

Fiddle is a tool for studying the compilation and execution of smallish programs written in C or C++. If you want to know what the compiler does to your code and why your code is slow, Fiddle can help.

It makes it easy to ask and answer interesting questions about what happens to programs as they go from source code to running program. Fiddle can run on its own, but it is built to work with Jupyter Notebook/Jupyter Lab to support interactive exploration.

It's features include:

1. Support for compiled languages like C and C++.
2. Control Flow Graph (CFG) generation from compiled code.
3. Easy support for varying build-time and run-time paremeters.
4. Easy, unified parameter and data gathering across building and running code.
5. Works great with Pandas and Jupyter Notebook/Lab.

The best way to learn about Fiddle is to try it. You can run the examples (this can take a while to load).

Or run it locally with Docker:

docker run -it --publish published=8888,target=8888 stevenjswanson/fiddle:latest jupyter lab --LabApp.token=''

and then visit http://localhost:8888/lab/tree/README.ipynb.

You can also read the documentation.

Examples

What Does a for loop look like in assembly?

>>> from fiddle import * 
>>> sample = code(r""" 
...    extern "C"
...    int loop() {
...    int sum = 0;
...	   for(int i = 0; i < 10; i++) {
... 		sum += i;
...    }
...	   return sum;
... }
... """)
>>> asm = build(sample)[0].asm("loop")
>>> print(asm) # doctest: +SKIP
loop:
.LFB0:
    .cfi_startproc
    endbr64
    pushq    %rbp
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    movq    %rsp, %rbp
    .cfi_def_cfa_register 6
    movl    $0, -8(%rbp)
    movl    $0, -4(%rbp)
.L3:
    cmpl    $9, -4(%rbp)
    jg    .L2
    movl    -4(%rbp), %eax
    addl    %eax, -8(%rbp)
    addl    $1, -4(%rbp)
    jmp    .L3
.L2:
    movl    -8(%rbp), %eax
    popq    %rbp
    .cfi_def_cfa 7, 8
    ret
    .cfi_endproc

Or, if you prefer a CFG:

>>> build(sample)[0].cfg("loop", "readme_loop.png") 
'readme_loop.png'

What Does -O3 Do To That Loop?

>>> asm = build(sample, build_parameters=dict(OPTIMIZE="-O3"))[0].asm("loop")
>>> print(asm) # doctest: +SKIP
loop:
.LFB0:
    .cfi_startproc
	endbr64
	movl	$45, %eax
	ret
	.cfi_endproc
	

Local Installation

Fiddle depends on some system packages and python's wheel. Setup a virtual environment:

python -m venv fiddle-venv

Become root, so you can install the systetm packages with apt-get with

sudo bash
. fiddle-venv/bin/activate	
make install-prereqs
exit

Install fiddle:

. fiddle-venv/bin/activate
pip install .

Run the tests:

make test

Common Problems

Fiddle needs LD_LIBRARY_PATH set properly to work, and it can't set it itself reliably. If you get

OSError: libfiddle.so: cannot open shared object file: No such file or directory

You can update LD_LIBRARY_PATH with:

$(set-fiddle-ld-path)

Saving Your Work

If you want to save changes you make to any of the examples, you'll need to run docker something like this:

docker run -it --publish published=8888,target=8888 --mount type=bind,source=$HOME,dst=/home/jovyan -w /home/jovyan/fiddle_work/fiddle  stevenjswanson/fiddle:latest  jupyter lab --LabApp.token=''