[cfe-dev] exhaustiveness of CSA checkers

[Fernandez, Matthew via cfe-dev]

Hi Gabor,

Thanks for your reply. The checker I’m implementing is similar to PthreadLockChecker. It knows the correct acquire/release patterns for certain primitives and checks for them. If analysis fails to reach the end of a function, the checker cannot warn for e.g. unreleased locks.

This is a somewhat unorthodox case as I know the target code to which this will be applied. All functions are <500LoC and the only loops are statically bounded. It is observable statically that all functions terminate and there are a finite number of paths.

I was hoping to use CSA for this because it handles path enumeration and constructing the exploded graph very nicely. Someone suggested to me I might have to move to KLEE, but that would be a shame because I’d need to introduce some code instrumentation/annotation to achieve what I want. Another option would be to use an AST visitor to enumerate the paths myself, but it would be nice to leverage LLVM’s existing functionality for this.

Thanks,
Matthew

From: Gábor Horváth <xazax at google.com>
Sent: Wednesday, January 15, 2020 08:13
To: Fernandez, Matthew <matthew.fernandez at intel.com>
Cc: cfe-dev at lists.llvm.org
Subject: Re: [cfe-dev] exhaustiveness of CSA checkers

Hi!

The clang static analyzer does not give you any guarantees regarding the coverage/exhaustiveness. There is no way to ensure exhaustive analysis (such analysis is likely to be unbounded for most non-trivial programs, so this is not only about runtime, but also termination). For this reason all the checks have to be implemented with non-exhaustiveness in mind.

Could you share what you are trying to achieve? Maybe symbolic execution is not the right tool for that problem.

Cheers,
Gabor

On Wed, Jan 15, 2020 at 12:58 AM Fernandez, Matthew via cfe-dev <cfe-dev at lists.llvm.org<mailto:cfe-dev at lists.llvm.org>> wrote:
Hello cfe-dev,

In prototyping a custom checker for the Clang Static Analyzer, I’ve found analysis terminates at some complexity limit. That is, when your target function exceeds some complexity bound, CSA stops path traversal and your checker does not receive callbacks for any remaining unvisited nodes. The two specific scenarios where I’ve run into this are high-iteration-count loops and complex conditionals (multiple short circuiting && and || operators). The first I can work around by rephrasing the target loops or something like -analyzer-max-loop, but I can’t find a way to affect the behavior of the second. To compound the situation, I cannot see how the checker can detect that path exploration was incomplete.

Is there a way to control the complexity limit enforced for conditionals? Or, failing that, to detect within the checker when path exploration was incomplete?

To give some more context, my checker is an experiment and not something I am intending to upstream. Runtime is not an issue; I am fine with the analyzer taking multiple hours for a single run. Though I understand why the existing CSA bound choices have been made, as most users do not want their compiler to run for this long.

Please CC me in replies as I’m not subscribed.

Thanks,
Matthew
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