CompCert VS codeql

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"

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.

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.

[1]: https://compcert.org/

CompCert sends its regards

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.

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.

Does anybody know how does this compare to https://compcert.org/ ?

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 .

apologies if this should be a discussion/issue/whatever but:

Do you envision going up against CodeQL and/or <https://www.jetbrains.com/help/qodana/about-qodana.html> by making semantic information available to the ast nodes? OT1H, I can imagine it could be an overwhelming increase in project scope, but OTOH it could also truly lead to some stunning transformation patterns

e.g. https://github.com/github/codeql/blob/v1.27.0/java/ql/exampl... or even more "textual" semantics such as

  var foo = "hello".substring(1); // knowing "foo" is a String

While not trivial because it is not documented, you can create your a database with your own facts. Some of the extractors that create the required files are open source https://github.com/github/codeql/blob/main/ruby/extractor/sr...

Efforts: Dependabot, CodeQL, Coverity, facebook's Infer tool, etc

> But why not for instance use a build system in some "container"?

I am not sure how this helps.

> I think the project could "bother" contributors with something like that, couldn't it?

Which project?

> An embedded C developer I've talked with quite often on some other forum, who imho is quite competent, said that Coverity is a poor tool that generates way too much false negatives and overlooks at the same time glaring issues.

He likely violated a license agreement with Coverity, since no one is allowed to say anything comparing Coverity to anything else.

> Said that's mostly an issue with all OpenSource tools for static C analysis.

I have been filing bug reports.

> OTOH the commercial ones are very expensive usually, with a target market of critical things like aviation of safety systems in cars and military use, places where they spend billions on projects. Nothing there for the average company, and especially not for (frankly often underfunded) OpenSource projects.

So you understand my pain.

> CodeQL? It's mostly an semantic search and replace tool, as I know? Is it that helpful? (I had a look, but the projects I'm working on don't require it. One would just use the IDE. No need for super large-scale refactorings, across projects, in our case).

I have never heard about this function. It is a static analyzer whose checks are written in the CodeQL language. However, it is very immature. When github acquired it, they banished the less reliable checks to the extended-and-security suite, leaving it only with about ~50 checks for C/C++ code. Those catch very little, although in the rare instances that they do catch things, the catches are somewhat amazing. Unfortunately, at least one of those checks provides technically correct, yet difficult to understand, explanations of the problem, so most developers would dismiss its reports as false positives despite it being correct:

https://github.com/github/codeql/issues/11744

There are probably more issues like that, but I have yet to see and report them.

> SonarCloud, hmm… This one I've used (around web development though). But am not a fan of. It bundles other "scanner" tools, with varying quality and utility. At least what they had for the languages I've actively used it was mostly about "style issues". And when it showed real errors, the IDE would do the same… (The question then is how this could be committed in the first place. But OK, some people just don't care. For them you need additional checks like SonarCloud I guess.)

It is supposed to be able to integrate into github's code scanning feature, so any newly detected issues are reported in the PR that generated them. Anyway, it is something that I am considering. I wanted to use it much sooner, but it required authorization to make changes to github on my behalf, which made me cautious about the manner in which I try it. It is basically at the bottom of my todo list right now.

> Wouldn't it be easy to add at least this to the build by using some "build container"?

I do not understand your question. To use it, we need a few things:

1. To be able to show any newly introduced defect reports in the PR that generated them shortly after it was filed.

2. To be able to scan the kernel modules since right now, it cannot due to a bad interaction between the build system and how compiler interposition is done. As of a few days ago, I have a bunch of hacks locally that enable kernel module scans, but this needs more work.

> Well, that's why I think something equivalent to `-Wall -Werror` should be switched on before writing the first line of code, in any language.

OpenZFS has had that in place for more than a decade. I do not know precisely when it was first used (although I could look if anyone is particularly interested), but my guess is 2008 when ZFSOnLinux started. Perhaps it was done at Sun before then, but both events predate me. I became involved in 2012 and it is amazing to think that I am now considered one of the early OpenZFS contributors.

Interestingly, the earliest commits in the OpenZFS repository referencing static analysis are from 2009 (with the oldest commit being from 2008 when ZFSOnLinux started). Those commits are ports of changes from OpenSolaris based on defect reports made by Coverity. There would be no more commits mentioning static analysis until 2014 when I wrote patches fixing things reported by Clang's static analyzer. Coverity was (re)introduced in 2016.

As far as the current OpenZFS repository is concerned, knowledge of static analysis died with OpenSolaris and we lost an entire form of QA until we rediscovered it during attempts to improve QA years later.

> But I guess I will stay with engraving my data into solid rock. Proven for at least hundred thousand years.

That method is no longer reliable due to acid rain. You would need to bury it in a tomb to protect it from acid rain. That has the pesky problem of the pointers being lost over time.

> At least someone needs to preserve the cat pictures and meme of our current human era for the cockroach people of the distant future. I'm not sure they will have a compatible Linux kernel and compiler available to build the ZFS drivers, or even punch card readers…

Github's code vault found a solution for that:

https://github.com/github/archive-program/blob/master/GUIDE....

I vaguely recall another effort trying to include the needed hardware in time capsules, but I could be misremembering.

Exceptions would be systems like CodeQL, but that's a bit out of scope for a game like WoW.