package lintcstubs-gen

Lintcstubs — Static analyzer for OCaml C primitives

These are a suite of tools for finding bugs in OCaml C stubs.

• lintcstubs_genwrap generates __wrap_ wrappers all C primitives with assertion checks for the type of arguments and return values.
• lintcstubs_genmain generates a main function that spawns threads and calls all C primitives.
• lintcstubs a tool containing a static analysis pass for detecting race conditions from the incorrect use of the OCaml runtime lock

Currently they require OCaml 4.13+.

Installation

Using opam

opam install lintcstubs

Why?

Static analyzers built for C won't know about the special rules for OCaml GC safety, and they won't know how the OCaml values are laid out in memory.

The wrapper generated by genwrap can be used at runtime (to validate that the returned value have the right "shape"), by using binutils's -wrap feature. It can also be used by a static analyzer to detect issues at build time (e.g. returning an integer, but forgetting to wrap it with Val_int).

Static analyzers work better when given an entire program, thus lintcstubs_genmain is useful to generate an entrypoint. This avoids false positives about NULL dereferences (OCaml values are never NULL, the runtime will raise an exception instead). The generated main function also makes it explicit that these functions are invoked in a multi-threaded environment.

Caveats

• only some very basic shapes are supported currently (primitive types, arrays, tuples). When the shape is unknown no assertion check is done for that parameter/field.
• Is_block() tracking isn't precise for allocated values
• write some examples
• show example on how to use with GobPie

Usage:

Consult the official manual on how to implement C primitives correctly.

For static analysis

lintcstubs_arity_cmt ocamlfile.cmt >primitives.h
lintcstubs_genwrap ocamlfile.cmt >test_analyze.c
lintcstubs_genmain ocamlfile.cmt >>test_analyze.c

ocamlfile.cmt is a -bin-annot file for ocamlfile.ml. Your build system should've produced one, check that it is using the -bin-annot flag if not. You can also create one manually (add include and ocamlfind flags as necessary):

ocamlc -bin-annot -c ocamlfile.ml

Then run your static analyzer (in this case the goblint based lintcstubs):

lintcstubs --disable warn.integer --disable warn.info --disable warn.deadcode test_analyze.c ocamlfile_stubs.c

Where ocamlfile_stubs.c is your C primitives implementation corresponding to ocamlfile.ml.

For runtime checking

This requires the binutils linker:

lintcstubs_genwrap ocamlfile.cmt >test_wrap.c
ocamlc -c test_wrap.c
ocamlopt ocamlfile.ml test_wrap.o test_stubs.o -ccopt -Wl,-wrap,stub1,-wrap,stub2

Where stub1, stub2, etc. are the names of your C primitive implementations.

This mode is still under development.

How it works

This is part of a suite of static analysis tools for C stubs described in a paper submitted to the ICFP 2023 OCaml workshop.