CompCert
acsl-by-example
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CompCert | acsl-by-example | |
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36 | 1 | |
1,757 | 94 | |
1.6% | - | |
7.3 | 1.8 | |
19 days ago | almost 3 years ago | |
Coq | TeX | |
GNU General Public License v3.0 or later | MIT License |
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CompCert
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Differ: Tool for testing and validating transformed programs
A big problem is that proving that transformations preserve semantics is very hard. Formal methods has huge potential and I believe it will be a big part of the future, but it hasn't become mainstream yet. Probably a big reason why is that right now it's simply not practical: the things you can prove are much more limited than the things you can do, and it's a lot less work to just create a large testsuite.
Example: CompCert (https://compcert.org/), a formally-verified compiler AKA formally-verified sequence of semantics-preserving transformations from C code to Assembly. It's a great accomplishment, but few people are actually compiling their code with CompCert. Because GCC and LLVM are much faster[1], and have been used so widely that >99.9% of code is going to be compiled correctly, especially code which isn't doing anything extremely weird.
But as articles like this show, no matter how large a testsuite there may always be bugs, tests will never provide the kind of guarantees formal verification does.
[1] From CompCert, "Performance of the generated code is decent but not outstanding: on PowerPC, about 90% of the performance of GCC version 4 at optimization level 1"
- So you think you know C?
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Can the language of proof assistants be used for general purpose programming?
Also a C compiler (https://compcert.org/). I did exaggerate bit in saying that anything non-trivial is "nearly impossible".
However, both CompCert and sel4 took a few years to develop, whereas it would only take months if not weeks to make versions of both which aren't formally verified but heavily tested.
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A Guide to Undefined Behavior in C and C++
From my experience, while many MCUs have settled for the big compilers (GCC and Clang), DSPs and some FPGAs (not Intel and Xilinx, those have lately settled for Clang and a combination of Clang and GCC respectively) use some pretty bespoke compilers (just running ./ --version is enough to verify this, if the compiler even offers that option). That's not necessarily bad, since many of them offer some really useful features, but error messages can be really cryptic in some cases. Also some industries require use of verified compilers, like CompCert[1], and in such cases GCC and Clang just don't cut it.
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Recently I am having too much friction with the borrow checker... Would you recommend I rewrite the compiler in another language, or keep trying to implement it in rust?
CompCert sends its regards
- Rosenpass – formally verified post-quantum WireGuard
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OpenAI might be training its AI technology to replace some software engineers, report says
But that's fine, because we can do even better with things like the CompCert C compiler, which is formally proven to produce correct asm output for ISO C 2011 source. It's designed for high-reliability, safety-critical applications; it's used for things like Airbus A380 avionics software, or control software for emergency generators at nuclear power plants. Software that's probably not overly sophisticated and doesn't need to be highly optimized, but does need to work ~100% correctly, ~100% of the time.
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There is such thing called bugfree code.
For context, CompCert is a formally verified compiler. My former advisor helped with a fuzzer called CSmith which found plenty of bugs in GCC and LLVM but not in CompCert.
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Checked C
Does anybody know how does this compare to https://compcert.org/ ?
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Proofs about Programs
This is a common property for proof-oriented languages. Coq shares this property for instance, and you can write an optimizing C compiler in Coq: https://github.com/AbsInt/CompCert .
acsl-by-example
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Why the C Language Will Never Stop You from Making Mistakes
Yes, Frama-C uses a plugin architecture, and there are plugins to verify all kinds of things, including functional correctness. The Frama-C tutorials page,
https://frama-c.com/html/tutorials.html
Has a link to the ACSL-by-example PDF which gives examples of creating in C various C++ STL inspired data structures and routines:
https://github.com/fraunhoferfokus/acsl-by-example/blob/mast...
Also, it is less effort to write bug-free code in OCaml than C. The Coq/Gallina proof assistant even has an OCaml-extraction (and also Haskell-extraction) feature where you extract runnable code from a formally verified algorithm in the Gallina specification language. (It's generally easier to proof theorems about code in the theorem prover itself, go figure.) Most of these C verification tools are written in OCaml, not C, with varying levels of assistance from Coq/Gallina.
The main reason the functional languages make it easier is because you generally execute side-effect free functions on data structures to give them the mathematical property you want. For example, you execute a lexicographical sort function on a list of strings and then the strings in the list all satisfy the mathematical property of a total ordering. You don't have to do any reasoning about the "in-between state" where pointers under the hood are being manipulated, and you don't have to add pre-conditions and post-conditions about the global environment if the code is side effect free and does not access non-local memory.
What are some alternatives?
seL4 - The seL4 microkernel
sol2 - Sol3 (sol2 v3.0) - a C++ <-> Lua API wrapper with advanced features and top notch performance - is here, and it's great! Documentation:
coq - Coq is a formal proof management system. It provides a formal language to write mathematical definitions, executable algorithms and theorems together with an environment for semi-interactive development of machine-checked proofs.
hacl-star - HACL*, a formally verified cryptographic library written in F*
unbound - Replib: generic programming & Unbound: generic treatment of binders
RecordFlux - Formal specification and generation of verifiable binary parsers, message generators and protocol state machines
gcc
spark-by-example - SPARK by Example is an adaptation of ACSL by Example for SPARK 2014, a programming language which is a formally verified subset of Ada
vericert - A formally verified high-level synthesis tool based on CompCert and written in Coq.
corn - Coq Repository at Nijmegen [maintainers=@spitters,@VincentSe]
koika - A core language for rule-based hardware design 🦑