Summary:
This diff extends the alias domain, so each variable can have multiple aliases.
It changed `KeyLhs` can be mapped to multiple alias targets in the `AliasMap` domain:
```
before : KeyLhs.t -> KeyRhs.t * AliasTarget.t
after : KeyLhs.t -> KeyRhs.t -> AliasTarget.t
```
Reviewed By: ezgicicek
Differential Revision: D18062178
fbshipit-source-id: b325a6055
Summary:
This diff tries to make less imprecise division by constants results.
For example, the results of the division `[l, u] / c`, where `c` is a positive constant, are:
1. If `l/c` or `u/c` is representable in the bound domain, it uses the precise bounds, i.e., `[l/c, u/c]`.
2. If it is not representable, it tries to make conservative results:
if `0<=l<=u`, it returns `[0, u]` because `0 <= [l/c, u/c] <= u`
if `l<=u<=0`, it returns `[l, 0]` because `l <= [l/c, u/c] <= 0`
if `l<=0<=u`, it returns `[l, u]` because `l <= [l/c, u/c] <= u`
3. otherwise, it returns top, `[-oo, +oo]`
Reviewed By: ezgicicek
Differential Revision: D18270380
fbshipit-source-id: 8fb14c0e4
Summary:
Add precision to analysis by elaborating the thread-status domain. This is done by having unknown (bottom), UI, BG or Any (both/top) elements in the lattice. This way, when we branch on thread-identity (if I am on UI thread do this, otherwise do that), we know that in one branch we are on UI thread and on the other we are *not* on the UI thread (BG thread), where previously the other branch would just go to top.
With this knowledge we can throw away pairs that come from callees which run on a thread that is impossible, given the current caller thread identity. This can happen when annotations are used incorrectly, and since this is the purview of annot-reachability, we just drop those pairs entirely.
Reviewed By: skcho
Differential Revision: D18202175
fbshipit-source-id: be604054e
Summary:
Steal a page from RacerD (and improve interface of) on using certain calls to assert
execution on a particular thread. Reduces FPs and FNs too.
Reviewed By: dulmarod
Differential Revision: D18199843
fbshipit-source-id: 5bdff0dfe
Summary:
The zero cost of node does not make sense especially when the abstract memory is non-bottom. This
resulted in unreasonable zero cost results sometimes, e.g. when the checker could not find
appropriate control varaibles having interval values of iteration. This diff fixes this, so sets
the minimum basic cost as 1, if the abstract memory at the node is non-bottom.
Reviewed By: ezgicicek
Differential Revision: D18199291
fbshipit-source-id: b215d10e5
Summary:
This adds a more interesting value domain to pulse: concrete intervals.
There are still two main limitations:
1. arithmetic operations are all over-approximated: any assignment involving arithmetic operations is replaced by non-determinism
2. abstract values that are discovered to be equal are not merged into one
Reviewed By: skcho
Differential Revision: D18058972
fbshipit-source-id: 0492a590f
Summary:
This does several things because it was hard to split it more:
1. Split most of the arithmetic reasoning to PulseArithmetic.ml. This
doesn't need to be reviewed thoroughly because an upcoming diff
changes the domain from just `EqualTo of Const.t` to an interval domain!
2. When going through a prune node intra-procedurally, abduce arithmetic
facts to the pre (instead of just propagating them). This is the "assume
as assert" trick used by biabduction 1.0 too and allows to propagate
arithmetic constraints to callers.
3. Use 2 when applying summaries by pruning specs whose preconditions
have un-satisfiable arithmetic constraints.
This changes one of the tests! Pulse now does a bit more work to find
the false positive, as can be seen in the longer trace.
Reviewed By: skcho
Differential Revision: D18117160
fbshipit-source-id: af3b2c8c0
Summary:
Primitive types are not annotated. Because of that, we used to implicitly derive
`DeclaredNonnull` type for them. This worked fine, but this leads to errors in Strict mode, which does
not believe DeclaredNonnull type.
Now lets offifically teach nullsafe that primitive types are
non-nullable.
Reviewed By: jvillard
Differential Revision: D18114623
fbshipit-source-id: 227217931
Summary: It is now possible to push the thread status into each critical pair. This leads to higher precision, because when code branches on whether it is on the UI thread, the final abstract state of the procedure will be `AnyThread`, but pairs created in the UI thread branch should know that their status is `UIThread`, not `AnyThread`.
Reviewed By: jvillard
Differential Revision: D18114273
fbshipit-source-id: cbb99b46f
Summary:
This diff avoids making top values on unknown non-static function,
such as abstract function, calls. This is necessary because the
generated top values ruin the precision of the cost checker.
Reviewed By: ezgicicek
Differential Revision: D17418611
fbshipit-source-id: aeb759bdd
Summary:
The wrong function was used when we tried to see if the class is
annotated with NullsafeStrict. This made it work only for non-static
methods.
Now we use the proper way.
Reviewed By: ngorogiannis
Differential Revision: D18113848
fbshipit-source-id: 02b7555be
Summary:
Previously, we considered a function which modifies its parameters to be impure even though it might not be modifying the underlying value. This resulted in FPs like the following program in Java:
```
void fresh_pure(int[] a) {
a = new int[1];
}
```
Similarly, in C++, we considered the following program as impure because it was writing to `s`:
```
Simple* reassign_pure(Simple* s) {
s = new Simple{2};
return s;
}
```
This diff fixes that issue by starting the check for address equivalnce in pre-post not directly from the addresses of the stack variables, but from the addresses pointed to by these stack variables. That means, we only consider things to be impure if the actual values pointed by the parameters change.
Reviewed By: skcho
Differential Revision: D18113846
fbshipit-source-id: 3d7c712f3
Summary: We stop tracking at builder boundaries. Let's tract create methods as well so that trace is more informative.
Reviewed By: skcho
Differential Revision: D18038637
fbshipit-source-id: a99b6431f
Summary:
This is the first take on strict mode semantics.
The main invariant of strict mode is the following:
If the function passes `NullsafeStrict` check and its return value is
NOT annotated as Nullable, then the function does not indeed return
nulls, subject to unsoundness issues (which should either be fixed, or
should rarely happen in practice).
This invariant helps the caller in two ways:
1. Dangerous usages of non strict functions are visible, so the caller is enforced to check them (via assertions or conditions), or strictify them.
2. When the function is strict, the caller does not need to worry about
being defensive.
Biggest known issues so far:
1. Condition redundant and over-annotated warnings don't fully
respect strict mode, and this leads to stupid false positives. (There is
so much more stupid false positives in condition redundant anyway, so
not particularly a big deal for now).
2. Error reporting is not specific to mode. (E.g. we don't distinct real nullables and non-trusted non-nulls, which can be misleading). To be
improved as a follow up.
Reviewed By: artempyanykh
Differential Revision: D17978166
fbshipit-source-id: d6146ad71
Summary:
This is an intermediate nullability type powering future Strict mode.
See the next diff.
Reviewed By: artempyanykh
Differential Revision: D17977909
fbshipit-source-id: 2d5ab66d4
Summary: In preparation for improvements to the arithmetic reasoning.
Reviewed By: dulmarod
Differential Revision: D17977207
fbshipit-source-id: ee98e0772
Summary:
Domain for thread-type. The main goals are
- Track code paths that are explicitly on UI thread (via annotations, or assertions).
- Maintain UI-thread-ness through the call stack (if a callee is on UI thread then the
trace any call site must be on the UI thread too).
- If we are not on the UI thread we assume we are on a background thread.
- Traces with "UI-thread" status cannot interleave but all other combinations can.
- We do not track other annotations (eg WorkerThread or AnyThread) as they can be
erroneously applied -- other checkers should catch those errors (annotation reachability).
- Top is AnyThread, and is used as the initial state for analysis.
Interestingly, by choosing the right strategy for choosing initial state and applying callee summaries gets rid of some false negatives in the tests even though we have not introduced any path sensitivity yet.
Reviewed By: jvillard
Differential Revision: D17929390
fbshipit-source-id: d72871034
Summary:
bigmacro_bender
There are 3 ways pulse tracks history. This is at least one too many. So
far, we have:
1. "histories": a humble list of "events" like "assigned here", "returned from call", ...
2. "interproc actions": a structured nesting of calls with a final "action", eg "f calls g calls h which does blah"
3. "traces", which combine one history with one interproc action
This diff gets rid of interproc actions and makes histories include
"nested" callee histories too. This allows pulse to track and display
how a value got assigned across function calls.
Traces are now more powerful and interleave histories and interproc
actions. This allows pulse to track how a value is fed into an action,
for instance performed in callee, which itself creates some more
(potentially now interprocedural) history before going to the next step
of the action (either another call or the action itself).
This gives much better traces, and some examples are added to showcase
this.
There are a lot of changes when applying summaries to keep track of
histories more accurately than was done before, but also a few
simplifications that give additional evidence that this is the right
concept.
Reviewed By: skcho
Differential Revision: D17908942
fbshipit-source-id: 3b62eaf78
Summary:
Java method annotations are ambiguous in that there is no difference between
annotating the return value of a method, and annotating the method itself.
The disambiguation is done entirely based on the meaning of the annotation.
Here, while `UiThread`/`MainThread` are genuine method/class annotations
and not return annotations, the reverse is true for `ForUiThread`/`ForNonUiThread`.
This means that these latter annotations do not determine the thread status of
the method they are attached to.
Here we fix that misunderstanding.
Reviewed By: jvillard
Differential Revision: D17960994
fbshipit-source-id: 5aecfb124
Summary: As per title. These test pass already because the previous thread domain was sufficient to express them. This won't necessarily be true when the whole-program analysis version comes around, because we may decide to not report on the `Threaded` elements (see domain).
Reviewed By: dulmarod
Differential Revision: D17930653
fbshipit-source-id: 2174f6b22
Summary:
- add the variable being declared so we can report it back in the trace in addition to its location
- distinguish between local vars and formals
Reviewed By: skcho
Differential Revision: D17930348
fbshipit-source-id: a5b863e64
Summary:
Eventually thread status will be stored inside every critical pair so as to allow path sensitivity. That means that the status can no longer be a whole trace, as this will quickly become intractable, because each domain element would have to maintain its own trace as well as its own thread-status trace.
This is not great, as we lose information here, but I don't see any other way around it that is not super complicated/costly (sharing will be limited when moving from callee to caller).
Other diffs up the stack will clean up infrastructure no longer used meaningfully (ie models and domains).
Reviewed By: mityal
Differential Revision: D17908908
fbshipit-source-id: 3bf353e33
Summary:
Starvation is currently path insensitive. Two special cases of sensitivity cover a large range of useful cases:
- sensitivity on whether the current thread is a UI/background thread;
- sensitivity on whether a lock can be acquired (without blocking) or not.
We add a few tests capturing some of the false positives and negatives of the current analysis.
Reviewed By: mityal
Differential Revision: D17907492
fbshipit-source-id: fbce896ac
Summary:
This diff adopts an array length evaluation function that is conservative. It is useful when our
domain cannot express length result precisely.
For example, suppose there is an array pointer `arr_locs` that may point to two arrays `a` and `b`,
and their lengths are `a.length` and `b.length` (symbols), respectively. Using the usual
evaluation, our current domain cannot express `a.length join b.length` (join of two symbolic
values), so it returns top.
In this case, we can use the conservative function intead. It evaluates the length as `[0,
a.length.ub + b.length.ub]`, since we know every array length is positive. The result is not
precise, but better than top.
Reviewed By: ezgicicek
Differential Revision: D17908859
fbshipit-source-id: 7c0b1591b
Summary:
Instead of a string argument named `~str` pass `Formal | Global` and let
`add_to_errlog` figure out how to print it.
Reviewed By: ezgicicek
Differential Revision: D17907657
fbshipit-source-id: ed09aab72
Summary:
When we make the decision to go into a branch "v = N" where some
abstract value is compared to a constant, remember the corresponding
equality. This allows to prune simple infeasible paths
intra-procedurally.
Further work is needed to make this useful interprocedurally, for
instance either or both of these ideas could be explored:
- abduce v=N in the precondition and do not apply summaries when the
equalities in the pre are not satisfied
- prune post-conditions that lead to unsat states where a value has to
be equal to several different constants
Reviewed By: skcho
Differential Revision: D17906166
fbshipit-source-id: 5cc84abc2
Summary:
When we know "x = 3" and we have a condition "x != 3" we know we can
prune the corresponding path.
Reviewed By: skcho
Differential Revision: D17665472
fbshipit-source-id: 988958ea6
Summary:
Let's add basic Java support to impurity checker. Since impurity checker relies on pulse, we need to add Java with Pulse callback as well. Pulse doesn't officially support Java yet, but we can enable it for impurity checker for now.
Many Java primitives/operations are not yet modeled (such as creation of new objects, support for collections etc.). Still, it is good to run impurity checker on the existing tests of the purity checker. Also, it is nice to see that we can identify most of the impure functions correctly in the purity dir. There are a lot of FNs though.
Reviewed By: skcho
Differential Revision: D17906237
fbshipit-source-id: 15308d285
Summary:
This diff introduces inequality for the iterator alias target, as we
did for the size target before.
Reviewed By: ezgicicek
Differential Revision: D17879208
fbshipit-source-id: cc2f6a723
Summary: If we have no pulse summary (most likely caused by pulse finding a legit issue with the code), let's consider the function as impure.
Reviewed By: jvillard
Differential Revision: D17906016
fbshipit-source-id: 671d3e0ba
Summary:
This diff revises the semantics of hasNext model to add the lengths of
arrays, rather than join them to top.
Reviewed By: ezgicicek
Differential Revision: D17882388
fbshipit-source-id: f5edaedb3
Summary:
[androidx.collection.SimpleArrayMap](https://developer.android.com/reference/androidx/collection/SimpleArrayMap.html) also has `keySet` and `entrySet` methods which make them eligible for inefficient keyset checker. Let's add it.
Title
Reviewed By: skcho
Differential Revision: D17831594
fbshipit-source-id: 32e831e18
Summary:
The current usage has several issues reducing code maintainability and
readability:
1. Null_field_access was misleading: it was used for checking accesing
to arrays as well!
2. But actually, when checking access to array via `length`, we sometimes
pretended it is a field access (hence very tricky code in rendering the
error).
3. "Call receiver consistency" is unclear name, was not obvious that it is all about
calling a method in an object.
Let's also consolidate code.
Reviewed By: artempyanykh
Differential Revision: D17789618
fbshipit-source-id: 9b0f58c9c
Summary: Before, we didn't track litho framework callees on client code which was wrong. Now, we replace this with the following: If the callee is `build()` itself or doesn't contain a `build()` in its summary, then we want to track it in the domain. The former makes sense since we always want to track `build()` methods. The latter also makes sense since such a method could be a setter for a prop (as in the case of `prop1` in `buildPropLithoOK` which we were missing before due to the imprecise heuristic that prevented picking up callees in litho).
Reviewed By: ngorogiannis
Differential Revision: D17810704
fbshipit-source-id: 87d88e921
Summary: As a heuristic, litho library calls on non-litho callers are not tracked. This is very imprecise and results in FPs and FNs as exemplified by newly added tests. Instead, we should check to see if the summary contains a `build()` method as will be done in the next diff. This diff adds these tests and refactors the test code.
Reviewed By: skcho
Differential Revision: D17809536
fbshipit-source-id: 6dff1868c
Summary:
Improve the trace by incorporating the callees and their locations in the call chain (i.e. chain of methods starting from `build()` call)
- extend the domain to contain the callee location
- replace the test results with the new traces
This makes our job much easier to debug FPs in a big codebase.
Reviewed By: skcho
Differential Revision: D17788996
fbshipit-source-id: 31938b5fe
Summary: `litho` checker contained two checkers: required-props and graphQL field accesses. Although they use the same domain, their reporting conditions and analysis details are different. However, they were bundled into the same analysis by adding disjunctions to `exec_instr` to handle both cases. Let's separate them into two different checkers, keeping a modular transfer function and analyzer that is reused by these two checkers.
Reviewed By: skcho
Differential Revision: D17788834
fbshipit-source-id: 47d77063b
Summary:
At some point it was thought that we can assume that any annotation starting with "On" means the method is on the UI thread.
That's too imprecise and has led to false positives and negatives. Restrict to a well-known safe set.
Reviewed By: ezgicicek
Differential Revision: D17769376
fbshipit-source-id: 0f8fee059
Summary:
This diff tries to narrowing the fixpoint of outermost loops, so that over-approximated widened values do not flow to the following code.
Problem: There are two phases for finding a fixpoint, widening and narrowing. First, it finds a fixpoint with widening, in function level. After that, it finds a fixpoint with narrowing. A problem is that sometimes an overly-approximated, imprecise, values by widening are flowed to the following loops. They are hard to narrow in the narrowing phase because there is a cycle preventing it.
To mitigate the problem, it tries to do narrowing, in loop level, right after it found a fixpoint of a loop. Thus, it narrows before the widened values are flowed to the following loops. In order to guarantee the termination of the analysis, this eager narrowing is applied only to the outermost loops.
Reviewed By: ezgicicek
Differential Revision: D17740265
fbshipit-source-id: e2d454036
Summary:
This diff extends the alias domain to analyze loop with list comprehensions form in Java precisely.
```
list2 = new List();
for (Element e : list1) {
list2.add(e);
}
```
1. `IteratorOffset` is a relation between a iterator offset and a length of another array. For example, in the above example, after n-times of iterations, the offset of the iterator (if it exists) and the length of `list2` are the same as `n`.
2. `IteratorHasNext` is a relation between iterator and its `hasNext` result.
3. At the conditional nodes, it prunes the alias list length of `list2` by that of `list1`.
* if `hasNext(list1's iterator)` is true, `list2`'s length is pruned by `< list1's length`
* if `hasNext(list1's iterator)` is false, `list2`'s length is pruned by `= list1's length`
Reviewed By: ezgicicek
Differential Revision: D17667128
fbshipit-source-id: 41fb23a45
Ezgi Çiçek
Sungkeun Cho
Dulma Churchill
Nikos Gorogiannis
Jules Villard
Mitya Lyubarskiy