Summary:
Previously we would say that `lhs <= rhs` (or `lhs |- rhs`) when a
mapping existed between the abstract addresses of `lhs` and `rhs` such
that `mapping(lhs)` was a supergraph of `rhs`. In particular,
we had that `x |-> x' * x' |-> x'' |- x |-> x'`. This is not entirely
great, in particular once we get pairs of state representing footprint +
current state. I'm not sure I have an extremely compelling argument why
though, except that it's not the usual way we do implication in SL, but
there wasn't a compelling argument for the previous state of affairs
either.
This changes `|-` to be true only when `mapping(lhs) = rhs` (modulo only
considering the addresses reachable from the stack variables).
Reviewed By: jberdine
Differential Revision: D14568272
fbshipit-source-id: 1bb83950e
Summary: This helps convergence when `<=` is based on physical equality for example, and widening is implemented as `widen ~prev ~next = join prev next`.
Reviewed By: skcho
Differential Revision: D14568270
fbshipit-source-id: ded5ed296
Summary:
Open fewer sessions by wrapping AI operations together in the same HTML
node session. This allows us to also print more stuff, such as whether
the current loop computation has converged.
Reviewed By: skcho
Differential Revision: D14568274
fbshipit-source-id: d47110cf4
Summary:
This fixes (if in a hackish way) an inherently quadratic behaviour in
the disjunctive domain when analysing loops: If you start with some
disjuncts `D1 \/ ... \/ Dn` and go once around the loop, you will end up
with disjuncts `(D1 \/ ... \/ Dn) \/ (D1' \/ ... \/ Dn')` assuming that
for all `i`, `{ Di } body of loop { Di' }` (in practice there is the
added difficulty that the post of the body of the loop can be a
disjunction too instead of a single abstract state). Assuming this isn't
a fixpoint, we would then go around the loop again from `D1`, ..., `Dn`,
`D1'`, ..., `Dn'`. However we already know what the posts of `D1` to `Dn`
are!
This attempts to curb duplicate work by marking the disjuncts in `prev`
as "visited" and instructing symbolic execution to skip visited states.
Then, once convergence is detected (from within `widen` for now) we mark
again all states as unvisited so that whatever is after the loop gets
symbolically executed.
This is a hack because ideally the AI scheduler would know about
disjunctive domain and schedule individual disjuncts for analysis.
However that would be a much bigger change. Let's see if the hack is
enough for now.
Reviewed By: mbouaziz
Differential Revision: D14258491
fbshipit-source-id: 21454398c
Summary:
When joining two lists of disjuncts we try to ensure there isn't a state
that under-approximates another already in the list. This helps reduce
the number of disjuncts that are generated by conditionals and loops.
Before we would always just add more disjuncts unless they were
physically equal but now we do a subgraph computation to assess
under-approximation.
We only do this half-heartedly for now however, only taking into
consideration the "new" disjuncts vs the "old" ones. It probably makes
sense to do a full quadratic search to minimise the number of disjuncts
from time to time but this isn't done here.
Reviewed By: mbouaziz
Differential Revision: D14258482
fbshipit-source-id: c2dad4889
Summary:
The disjunctive domain shouldn't really be a set in the first place as
comparing abstract states for equality is expensive to do naively
(walking the whole maps representing the abstract heap). Moreover in
practice these sets have a small max size (currently 50 for pulse, the
only client), so switching them to plain lists makes sense.
Reviewed By: mbouaziz
Differential Revision: D14258489
fbshipit-source-id: c512169eb
Summary:
`AnalyzerNodesBasicCost` is just mapping instructions to abstract costs, it doesn't need to use AI.
Also it was keeping a map (node -> cost) for each node, this is completely removed.
Depends on D14028171
Reviewed By: ddino
Differential Revision: D14028249
fbshipit-source-id: 63f39261a
Summary:
- There is no need to use AI to compute a dot product: let's just fold over all nodes, but still do it in order (using the WTO) to report at the right place
- The previous version was computing a dot product on nodes for each node, which was quadratic, the new version is linear
- Report only once, the first time the threshold is reached (if in a loop, report at the loop head)
Reviewed By: ddino
Differential Revision: D14028171
fbshipit-source-id: b4a840c6e
Summary:
This will allow disjunctive analyzers to return sets of states as a
result instead of always returning one state. More precisely, this will
be needed for pulse when it becomes inter-procedural, if we take
summaries of functions to be disjunctive too (like, e.g., biabduction
does with several specs per function).
Reviewed By: mbouaziz
Differential Revision: D13537601
fbshipit-source-id: f54caf802
Summary:
Introduce machinery to do disjunctive HIL domains and use it for pulse,
but only in a mode that preserves the existing behaviour.
The disjunctive domain is a functor that turns any (HIL for now)
transfer function module into one operating on sets of elements of the
original domain. The behaviour of joins (and widenings, which are equal
to joins) can be chosen when instantiating the functor among 3
behaviours:
- `` `JoinAfter n`: when the set of disjuncts gets bigger than `n` the
underlying domain's join is called to collapse them into one state
- `` `UnderApproximateAfter n`: when the sest of disjuncts gets bigger
than `n` then just stop adding new states to it, drop any further states
on the floor. This corresponds to an under-approximation/bounded
approach.
- `` `NeverJoin`
The widening is always of the form ``
`UnderApproximateAfterNumIterations max_iter` for now since the only
user is pulse and I'm not sure what else would be useful.
Picking `` `JoinAfter 0` gives the same results as the non-disjunctive
domain since the underlying `join` will always be called. Make pulse use
this mode for now, and tune it in a next diff.
Reviewed By: mbouaziz
Differential Revision: D13431375
fbshipit-source-id: b93aa50e7
Summary:
A lot of functors that take a `Make{SIL,HIL}` can take a `{SIL,HIL}`
directly instead. This makes my head hurt a bit less.
Reviewed By: mbouaziz
Differential Revision: D13416967
fbshipit-source-id: eb0b33bc4
Summary:
`AccessExpression.t` and `HilExp.t` are about to become mutually
recursive, this will help distinguish the actual changes from the moving
of code around.
This deletes the file left around in the previous commit to preserve
callers of `AccessExpression`.
Reviewed By: mbouaziz
Differential Revision: D13377645
fbshipit-source-id: 71338d1f3
Summary:
It's useful for checkers to know when variables go out of scope to
perform garbage collection in their domains, especially for complex
domains with non-trivial joins. This makes the analyses more precise at
little cost.
This could have been added as a custom function call to a builtin, but I
decided against it because this instruction doesn't have the semantics
of any function call. It's better for each checker to explicitly not
deal with the custom instruction instead.
Reviewed By: jberdine
Differential Revision: D13102951
fbshipit-source-id: 33be22fab
Summary:
I hear that this scheduler is better. I want the best scheduler
possible. Also pulse's join is a bit complex so it might matter one day.
whydididothis
Reviewed By: mbouaziz
Differential Revision: D12958131
fbshipit-source-id: 3bd77ccba
Summary:
This may help running the id map bookkeeping on its own in the future
and makes the code slightly more readable in my opinion.
Reviewed By: mbouaziz
Differential Revision: D12858066
fbshipit-source-id: fea4aea63
Summary:
HIL wanted to do its own HTML printing, causing code duplication and hacks to
avoid double opening/closing files. Instead, pass a hook to print SIL
instructions or not.
This also makes the debug HTML be printed even in case of raised exceptions,
which is invaluable to debug crashes or even just reports in the case of
checkers that can raise `Stop_analysis` (pulse only for now).
This also print intermediate abstract states between instructions instead of
only at the start and end of nodes, for moar debugging.
Reviewed By: mbouaziz
Differential Revision: D12857425
fbshipit-source-id: 4ee6c88d6
Summary: Make the whole type private, introduce constructors for each variant, and deal with the consequences.
Reviewed By: da319
Differential Revision: D12825810
fbshipit-source-id: a01922812
Summary:
Seems useful to know when we're printing one instruction only, but not when we
print lots of them for readability.
Reviewed By: mbouaziz
Differential Revision: D12823481
fbshipit-source-id: 2beb339f2
Summary:
It terminates narrowing when new and old states are not comparable.
Since current narrowing does not use meet operations guaranteeing
termination of narrowing, it tries to terminate narrowing more
conservatively.
Reviewed By: mbouaziz
Differential Revision: D12815419
fbshipit-source-id: e8b45199e
Summary:
Instead of propagating a partial state give up the analysis of the
function entirely on error. The state after an error is mostly
non-sensical so until we know better just giving up makes sure the
analysis remains sensible and produce fewer spurious warnings.
Reviewed By: mbouaziz
Differential Revision: D10483979
fbshipit-source-id: 171ec8469
Summary:
New analysis in foetal form to detect invalid use of C++ objects after their
lifetime has ended. For now it has:
- A domain consisting of a graph of abstract locations representing the heap, a map from program variables to abstract locations representing the stack, and a set of locations known to be invalid (their lifetime has ended)
- The heap graph is unfolded lazily when we resolve accesses to the heap down to an abstract location. When we traverse a memory location we check that it's not known to be invalid.
- A simple transfer function reads and updates the stack and heap in a rudimentary way for now
- C++ `delete` is modeled as adding the location that its argument resolves to to the set of invalid locations
- Also, the domain has a really crappy join and widening for now (see comments in the code)
With this we already pass most of the "use after delete" tests from the
Ownership checker. The ones we don't pass are only because we are missing
models.
Reviewed By: mbouaziz
Differential Revision: D10383249
fbshipit-source-id: f414664cb
Josh Berdine
Jules Villard
Mehdi Bouaziz
Nikos Gorogiannis
Daiva Naudziuniene
Sungkeun Cho
Ezgi Çiçek