[cfe-dev] [analyzer] Alpha checker statuses.
Artem Dergachev via cfe-dev
cfe-dev at lists.llvm.org
Wed May 22 14:04:19 PDT 2019
Mmm, i still don't understand what's the *purpose* of the beta package.
I can understand the idea of "here's a new checker, we addressed all
issues we know about but there may be other issues that we might have
missed, so please try it out if you're into this sort of stuff". For now
such checkers are usually outright turned on by default.
But you're proposing to put checkers into beta when they have known
classes of false positives that are relatively easy to fix. So it's not
for gathering feedback (we already have enough) and there's no plan on
addressing feedback rapidly either (because if you have the capability
to address feedback rapidly, there's no reason to start with feedback
not addressed). It sounds as if we'll still bounce back all the bug
reports against beta checkers with "hey, this is beta, we know it's
broken, right?". If that's the case, then they're not really different
from alpha checkers and i wouldn't be comfortable providing them to the
users.
On 5/22/19 10:57 AM, Kristóf Umann wrote:
> I implemented what we discussed here in the following manner: Each
> checker or checker option must either be in:
>
> * Alpha: Unfinished, users are strongly discouraged from using it.
> * Beta: Stable but might produce more false positives and the emitted
> reports might lack proper explanation
> * Released: Production ready, very few false positives with easy to
> understand bug reports.
>
> Any checker or checker option in addition can be marked as hidden,
> meaning that it's a developer feature.
>
> On Thu, 16 May 2019 at 01:24, Artem Dergachev <noqnoqneo at gmail.com
> <mailto:noqnoqneo at gmail.com>> wrote:
>
> Just wanted to also point out that help is very welcome with
> implementing the missing functionality in the checkers that we've
> been discussing here.
>
> (more replies inline)
>
> On 5/15/19 5:26 AM, Kristóf Umann wrote:
>> How about this:
>>
>> -analyzer-checker-help: Displays production ready (non-modeling)
>> checkers, and beta checkers with a disclaimer for each
>> description. Don't forget to patch clang-tidy!
>> -analyzer-checker-help-developer: Displays only developer
>> (modeling, debug) checkers (renamed from *-hidden).
>> -analyzer-checker-help-alpha: Displays only alpha (non-modeling)
>> checkers with very scary disclaimers both around the list and for
>> each checker description.
>>
>> Note how each of these is mutually exclusive. I think we
>> shouldn't make a flag that displays all checkers, but should
>> allow the following invocation to do so:
>>
>> clang -cc1 -analyzer-checker-help -analyzer-checker-help-alpha
>> -analyzer-checker-help-hidden
>
> This makes sense to me and i think this is how it should have
> always been done.
>
>
> Note that hidden checkers may only show up in
> -analyzer-checker-help-developer. Options for implicit checkers are
> NOT implicitly hidden, but options for alpha checkers are implicitly
> marked alpha.
>
>> On Wed, 15 May 2019 at 12:39, Kristóf Umann
>> <dkszelethus at gmail.com <mailto:dkszelethus at gmail.com>> wrote:
>>
>> + György Orbán
>>
>> On Wed, 15 May 2019 at 00:41, Artem Dergachev
>> <noqnoqneo at gmail.com <mailto:noqnoqneo at gmail.com>> wrote:
>>
>> I wanted to give more visibility to the discussion on the
>> status of
>> different Static Analyzer "alpha" (unfinished) checkers
>> that's going on
>> on Phabricator (https://reviews.llvm.org/D57858). Story
>> so far: We're
>> trying to figure out how many of them can be finished
>> with relatively
>> little effort (and therefore we should probably ask
>> around to gather
>> feedback) and how many are clearly not ready for any sort
>> of use and
>> should be hidden until the most glaring bugs are fixed.
>> For now we
>> officially treat all alpha checkers as the latter - so
>> don't use them!
>>
>> Just to add to the summary: despite our "disapproval" of
>> using alpha checkers, we always made them very visible, since
>> if you wanted to list the available checkers, you inevitable
>> came across them (and they are also lexicographically greater
>> than the rest of them).
>>
>> Due to the lack of branches in our SVN repository, we used
>> the alpha package to make development incremental, which
>> inevitable resulted in some checkers in there being
>> unfinished and unstable, while others merely need some
>> finishing touches, and could be used despite being rough
>> around the patches.
>>
>> rough around the edges*
>>
>> The discussion came up in a patch that plans to expose
>> checker options, that always existed but were never listable,
>> unless you read the source code. However, just like alpha
>> checkers, many of these also hide features under development,
>> while other would genuinely be useful to fine tune the
>> analyzer for a specific project.
>>
>> This discussion is important because different people's
>> codebases are
>> ridiculously different, so it's almost impossible to
>> estimate the
>> quality and usefulness of static analysis unless as many
>> varied
>> codebases as possible are involved.
>>
>> >>! In D57858#1500668, @Szelethus wrote:
>> > `IteratorChecker` is a prime example that still
>> suffers from not
>> ideal FP/TP ratio, but users at Ericsson value it plenty
>> enough not to
>> be bothered by it. Many of the changes here and in
>> private directly
>> address user bug reports (That's just one, but I do
>> remember having
>> others around too!).
>>
>> Once it has visitor path notes about where did it get its
>> iterators
>> from, some of the iterator checks should definitely be
>> considered for
>> being turned on by default. Especially the mismatched
>> iterator check
>> that doesn't rely on hardcore constraint solving. The
>> current upstream
>> version is not in good shape though; i just tried it on
>> LLVM and it
>> currently crashes all over the place with "Symbol
>> comparison must be a
>> `SymIntExpr`" assertion (pls ask me for repros if they
>> aren't obvious).
>> Also it has false mismatched iterator positives on
>> `A.insert(B.begin(),
>> B.end())`.
>>
>>
>> >> In https://reviews.llvm.org/D57858#1501065, @dkrupp
>> wrote:
>> > These are the alpha checkers that we are testing in
>> Ericsson:
>>
>> Let me undig my last year's attempt to take a look at
>> alpha checkers.
>> The most common "limb" to "miss" in the alpha checkers is
>> the "bug
>> visitor" functionality that'd add checker-specific path
>> notes to the
>> report, which is almost inevitably necessary for any
>> path-sensitive
>> checker. Bug reports without path notes are hard to
>> understand, but
>> that's one thing that your users won't tell you: they
>> often just don't
>> have their good taste to realize that bug reports
>> shouldn't be so hard
>> to understand. The users often take it for granted that
>> they have to
>> figure out themselves where do these values come from,
>> but it's still
>> our job to not force them to.
>>
>>
>> The fundamental problem here is, in my opinion, that "alpha"
>> doesn't describe many of these checkers too well. I think
>> once a checker is stable and has a "reasonable" true
>> positive/false positive ratio, we should move them out of
>> alpha status: not only would we be able to gather invaluable
>> feedback for these, but users might appreciate the feature
>> even with a couple shortcomings. However, just because they
>> are not falling apart on their own, these aren't always
>> production ready -- how about we introduce a "beta" package?
>>
>> Alpha checkers would be incomplete, incorrect and unstable by
>> definition, and would be hidden from non-developers. Beta
>> checkers would receive a disclaimer that they might emit too
>> much false positives to be production ready and don't emit
>> ideal bug reports in terms of readability, but are considered
>> stable and usable.
>>
>>
>> > alpha.core.BoolAssignment
>>
>> Yes, i agree that this one's pretty useful. It's
>> currently missing a
>> visitor that explains why does the analyzer think that
>> the value is
>> non-true/false, which is often necessary to understand
>> the warning.
>>
>> This would be an ideal candidate to be moved to a beta package.
>>
>
> I'll be comfy to move it straight to core as long as someone
> stuffs a `bugreporter::trackExpressionValue()` into it and we both
> test it and see no obvious FP patterns specific to this checker.
> Unless we do this, i probably won't be comfy putting it into beta :)
>
>>
>> > alpha.core.CastSize
>>
>> This one's indeed relatively quiet, but i'm seeing ~50
>> false positives
>> caused by stuffing metadata at the beginning of a
>> dynamically allocated
>> buffer. I.e., allocate a buffer that's 4 bytes larger
>> than necessary,
>> use these 4 bytes for our own bookkeeping and provide a
>> pointer to the
>> rest of the buffer to be used for the actual value. I
>> don't see an easy
>> way to fix these false positives, so i don't see how to
>> move this out of
>> alpha.
>>
>>
>> > alpha.core.Conversion
>>
>> Interestingly, i haven't seen this one trigger on our
>> codebases. So i
>> don't have an opinion here. There's a chance it might be
>> a good opt-in
>> check. Do you have an open-source project in mind on
>> which this check is
>> actually useful?
>>
>>
>> > alpha.core.DynamicTypeChecker
>>
>> I really root for enabling this checker (and generally
>> improving our
>> dynamic type-checking), but for now i'm seeing ~600 false
>> positives in
>> projects that use custom RTTI (something like `dyn_cast`)
>> and ~300 more
>> Objective-C-specific false positives. I can take a look
>> and try to
>> reduce some of the custom RTTI ones if you're interested
>> in figuring out
>> how to fix them; i don't remember if they are easy to fix.
>>
>>
>> > alpha.core.SizeofPtr
>>
>> This checker does indeed find interesting bugs sometimes,
>> but i'm
>> overwhelmed by ~300 false positives in which the sizeof
>> of a pointer is
>> taken intentionally. This is especially annoying when the
>> pointer is
>> hidden behind a typedef and the user doesn't need to know
>> whether it's a
>> pointer or not.
>>
>>
>> > alpha.core.TestAfterDivZero
>>
>> I don't see any positives of this checker, but this
>> checker is crazy and
>> shouldn't have been done this way. It's a "must-problem"
>> check and we
>> don't have any sort of infrastructure to even display
>> this kind of bug
>> report properly after we find it, let alone to properly
>> find it. We need
>> a more-or-less full-featured data flow analysis engine
>> before we make an
>> attempt on such checker.
>>
>>
>> > alpha.cplusplus.DeleteWithNonVirtualDtor
>>
>> I don't see any positives of this checker. Is it any
>> better than the
>> compiler warning that we have for all polymorphic classes
>> that have no
>> virtual destructors?
>>
>> Maybe this one too.
>>
>
> Dunno, why duplicate a compiler warning that's already on by
> default and more aggressive than the checker?
>
>>
>> > alpha.security.MallocOverflow
>>
>> This one's extremely loud for me (~1500 false positives).
>> It looks as if
>> it warns on every `malloc(x * sizeof(int))` (due to
>> potential integer
>> overflow during multiplication) so i just don't see it
>> working as an
>> AST-based check. We should probably rewrite it on top of
>> taint analysis
>> and then it'll need a constraint solver that knows how to
>> multiply things.
>>
>> Like, this is the point where i'd like to ask how does
>> this happen that
>> you don't see these false positives. Is this checker
>> actually quiet for
>> you? Or are your users addressing these warnings somehow?
>>
>>
>> > alpha.security.MmapWriteExec
>>
>> I don't see any positives of this checker. It probably
>> needs a visitor
>> (which is trivial) and it definitely needs a solution for
>> different
>> values of macros on different platforms that'd be better
>> than just
>> setting them as a config flag.
>>
>>
>> > alpha.security.ReturnPtrRange
>>
>> I don't see any positives of this checker. It definitely
>> needs a visitor
>> and we might as well join it with the generic array bound
>> checker. Also
>> need to figure out how to deal with, say, vector::end()
>> which is
>> supposed to return an out-of-bound pointer.
>>
>>
>> > alpha.security.taint.TaintPropagation
>>
>> I believe that the generic taint engine is currently very
>> solid, but
>> specific checks that we have on top of it are very much
>> unfinished: they
>> simply don't react on any sort of validation that can be
>> used to remove
>> the taint. Normally that'll involve consulting the
>> constraint manager
>> (in case of tainted integers) or modeling validation
>> routines (in case
>> of more complicated objects).
>>
>>
>> > alpha.unix.BlockInCriticalSection
>>
>> I have ~10 positives and i didn't have a look at them
>> back then; might
>> be good. This checker needs a visitor to explain why do
>> we think we're
>> in a critical section.
>>
>>
>> > alpha.unix.Chroot
>>
>> I don't see any positives of this checker. This checker
>> needs a visitor
>> to highlight chroot.
>>
>>
>> > alpha.unix.PthreadLock
>>
>> Uhm, i have a few patches on this checker that i never
>> committed:
>> - https://reviews.llvm.org/D37806
>> - https://reviews.llvm.org/D37807
>> - https://reviews.llvm.org/D37809
>> - https://reviews.llvm.org/D37812
>> - https://reviews.llvm.org/D37963
>> And it still needs a visitor. And support for more APIs,
>> 'cause there
>> are still false positives caused by unobvious POSIX APIs
>> that release
>> the mutex (sometimes conditionally). And once it's done,
>> i'll be seeing
>> no positives of this checker; it sounds like a good
>> checker to have, but
>> it doesn't seem to find mistakes that are *easy to make*.
>>
>>
>> > alpha.unix.SimpleStream
>> > alpha.unix.Stream
>>
>> Those need, at least:
>> - A bug visitor.
>> - A suppress-on-sink behavior. Otherwise they warn on
>> every assert
>> between open and close (~200 false positives for me).
>> - Pointer escape support.
>> Also i vaguely remember that the non-simple checker is
>> known to cause
>> more state splits than necessary.
>>
>>
>> > alpha.unix.cstring.NotNullTerminated
>>
>> Hmm, this check looks like a walking .addTransition() bug
>> (unintended
>> state split) when invoked from getCStringLength(). Also
>> it doesn't seem
>> to be disabled when the checker is disabled, so i guess
>> we're kinda
>> "using" it too. But it's also too quiet to matter, as it
>> pretty much
>> only warns when you're trying to compute a strlen() of a
>> function pointer.
>>
>>
>> > alpha.unix.cstring.OutOfBounds
>>
>> https://bugs.llvm.org/show_bug.cgi?id=41729 and it also
>> needs a visitor
>> for the index.
>>
>
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