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Added explanation of verifast.

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Tobias Reinhard 2022-12-28 20:52:48 -05:00
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Test/VeriFast/tasks/vTaskSwitchContext/README.md
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This directory contains an unbounded memory safety and thread safety proof
for the core of the task scheduler: `vTaskSwitchContext`
## VeriFast
[VeriFast](https://github.com/verifast/verifast)
is a deductive program verifier for C based on separation logic.
It supports verifying concurrent code and reasoning about complex data structures.
VeriFast proofs are *unbounded*.
That is, until explicitly specified, it does not assume any bound on the size of the involved data structures.
Hence, proofs give us unbounded guarantees.
In our case, this means that our proof holds for any number of tasks and any size of the involved data structures.
Reasoning about concurrent code can be tricky because of all the interleavings that can occur.
VeriFast does not assume anything about the occuring interleavings.
Therefore, the proven guarantees hold for every possible interleaving that might occur during runtime.
Being a deductive verifier, VeriFast requires us to manually write a proof.
In particular, we have to specify what well-formed data structures look like and to annotate the code with proof steps.
It then symbolically executes the annotated code and queries an SMT solver to check the validity of proof steps.
This directory contains all the specifications and proof steps necessary to check that the scheduler is memory and thread safe.
## Key Result
Informally, the proof guarantees the following:
```
Proof Assumptions: