[Clang Static Analyzer] Preliminary patch for checkInitialState
Gabor Kozar
kozargabor at gmail.com
Tue Dec 17 07:39:49 PST 2013
This does look fairly straightforward, and fairly good! But I'm
concerned
about the FunctionDecl parameter: the analyzer also allows
ObjCMethodDecls and BlockDecls to be analyzed as top-level entry
points.
Perhaps a PointerUnion3 would be the best thing to do here, at least
for
now? Or alternately, we allow people to specify which initial state
they're checking, either by having several callbacks or using a
template
parameter. What do you think?
Indeed, I haven't considered these. I personally really don't like the
idea of exposing a PointerUnion3. I think the best solution would be to
use templates, like check::PreStmt, except with Decl, of course.
Also, one nice thing about checkInitialState is that it can be
non-const,
since it is guaranteed to run 0 or 1 times before the checker is used
elsewhere. :-)
True enough. I'll look into it.
I think a NULL initial state means a checker has decided not to analyze
this function. Weird and unlikely, but possible. (For example, it
allows
us to move the -analyze-function option into a checker.)
Allowing a checker to make this decision on behalf of all the other
checkers... I'm not absolutely certain I like that idea.
It would indeed allow -analyze-function to become a checker, but I
would consider that a hack: conceptually, I wouldn't consider this the
job of a checker.
Besides -analyze-function, what would this enable? The only other thing
I can think of is forcing the analyzer off code paths that are somehow
known to the checker to be impossible. (I'm talking about allowing a
checker to set a NULL state in general, not just in checkInitialState).
That might be practical, I can imagine some uses, but it would also
require considerably more effort than this.
I'll think some more about this, but for the time being I would
disallow NULLs from checkInitialState.
Can you explain why you needed to move the getInitialState call
earlier? It seems dangerous to run checkers before we have a block
counter in place, since conjured symbols use the block count.
That was probably a mistake. Initially I thought to call the
checkInitialState callback outside getInitialState, and so I did a bit
of organizing the code around. I did not think this could be the issue.
I'll fix it, thanks!
I'm not sold on this one yet. I mean, I get the idea, but it again
seems
like something where we want a nicer interface than just "FunctionDecl"
(and at the very least need to handle ObjCMethodDecl as well). But we
can
discuss this later.
Also taking ObjCMethodDecl and BlockDecl into consideration, I'd say
lets create an EntryPointInfo class, that would basically just wrap a
PointerUnion3 (as an internal implementation detail), but would provide
more straightforward accessor methods like getDecl, getFunctionDecl,
getBlockDecl, as well as a get<T> and is<T>. This could also be
generalized and put to use in checkInitialState, and even in CallEvent
- I believe all we have right now is a const Decl* getDecl() there.
What do you think?
Finally, style notes (guessing this comes from bouncing between
projects):
Yeah, in general, I tried to use the style I saw in the surrounding
code, but I did not really pay attention to this. Will definitely fix
it, thanks for pointing it out.
At work, we're using clang-format to take care of these issues for us.
I guess I can also set it up for when I'm working on Clang. You're
using the LLVM style, right?
No, sorry. It's not that it's particularly destabilizing so much as
it's just well past the deadline for features and enhancements.
Fair enough. I will not hurry then.
Thanks for the help!
--
Gábor 'ShdNx' Kozár
kozargabor at gmail.com
On Mon, Dec 16, 2013, at 22:10, Jordan Rose wrote:
No, sorry. It's not that it's particularly destabilizing so much as
it's just well past the deadline for features and enhancements.
Jordan
On Dec 16, 2013, at 13:07 , Gabor Kozar <[1]kozargabor at gmail.com>
wrote:
Is there any chance of this making it into 3.4? If so, I can work (and
think) on it tomorrow, otherwise it can wait, obviously.
(Sorry for the short answer, had a long day.)
--
Gábor 'ShdNx' Kozár
[2]kozargabor at gmail.com
On Mon, Dec 16, 2013, at 18:50, Jordan Rose wrote:
This does look fairly straightforward, and fairly good! But I'm
concerned
about the FunctionDecl parameter: the analyzer also allows
ObjCMethodDecls and BlockDecls to be analyzed as top-level entry
points.
Perhaps a PointerUnion3 would be the best thing to do here, at least
for
now? Or alternately, we allow people to specify which initial state
they're checking, either by having several callbacks or using a
template
parameter. What do you think?
Also, one nice thing about checkInitialState is that it can be
non-const,
since it is guaranteed to run 0 or 1 times before the checker is used
elsewhere. :-)
- Handling NULL ProgramStateRef-s. I do not think it is reasonable to
have NULL as the initial state. Probably assert when a
checkInitialState call returns NULL?
I think a NULL initial state means a checker has decided not to analyze
this function. Weird and unlikely, but possible. (For example, it
allows
us to move the -analyze-function option into a checker.)
- Whether to call the checkInitialState callback in
ExprEngine::getInitialState, or where getInitialState is used. I found
one such method: CoreEngine::ExecuteWorkList. Logically - knowing
nothing of the codebase -, I think it makes sense to do this in
getInitialState. It does not appear to belong to CoreEngine, especially
since I cannot find any references to getCheckerManager() in
CoreEngine.
I agree. Can you explain why you needed to move the getInitialState
call
earlier? It seems dangerous to run checkers before we have a block
counter in place, since conjured symbols use the block count.
Do we have any checkers that can use this? Perhaps as proof-of-concept
you can move the check for main's argc and argv into a checker.
Once checkInitialState is working, I also plan to do a void
checkBeginFunction(const FunctionDecl*, CheckerContext&) const, i.e. a
callback that is called whenever a function is entered, either through
a function call (this would be triggered right after checkPreCall) or
when it is the entry point of the analysis.
I'm not sold on this one yet. I mean, I get the idea, but it again
seems
like something where we want a nicer interface than just "FunctionDecl"
(and at the very least need to handle ObjCMethodDecl as well). But we
can
discuss this later.
I think you'd implement this by calling checkBeginFunction right after
checkInitialState and also from ExprEngine::inlineCall (right after
"State->enterStackFrame(...)")
Finally, style notes (guessing this comes from bouncing between
projects):
+ if(!State) return NULL; // exit early in case of unfeasible state
Space after if, consequent statement on a separate line, comments also
on
a separate line (and in the form of a complete sentence, with
capitalization and a period).
Thank you for putting this together!
Jordan
On Dec 13, 2013, at 17:03 , Gabor Kozar <[3]kozargabor at gmail.com>
wrote:
Hi Jordan,
I had an issue recently with the Static Analyzer that I wouldn't be
able to detect when a function was entered - either through a call or
serving as the entry point of the analysis. (I ended up using
checkPreStmt and figuring out if we've been magically transported
inside a function body and check the program state whether the
necessary info was already recorded by checkPreCall. Not something I'd
call nice by any means.)
So I wrote to cfg-dev and you mentioned that you had no such callbacks
currently implemented, although they have been needed before, and that
patches were welcome. Since this is a fairly trivial project, I was
comfortable with doing it in my very limited free time (especially
because I still intend to work on the Static Analyzer open projects at
some point when I'm able).
Find the diff file attached. Since you've pointed me to
ExprEngine::getInitialState, I just modified it to call any checkers
registered for check::InitialState at the end. So the signature for the
callback is:
ProgramStateRef checkInitialState(const FunctionDecl*, ProgramStateRef)
const
There are a few things I'm not sure about:
- Handling NULL ProgramStateRef-s. I do not think it is reasonable to
have NULL as the initial state. Probably assert when a
checkInitialState call returns NULL?
- Whether to call the checkInitialState callback in
ExprEngine::getInitialState, or where getInitialState is used. I found
one such method: CoreEngine::ExecuteWorkList. Logically - knowing
nothing of the codebase -, I think it makes sense to do this in
getInitialState. It does not appear to belong to CoreEngine, especially
since I cannot find any references to getCheckerManager() in
CoreEngine.
Please let me know what you think!
Once checkInitialState is working, I also plan to do a void
checkBeginFunction(const FunctionDecl*, CheckerContext&) const, i.e. a
callback that is called whenever a function is entered, either through
a function call (this would be triggered right after checkPreCall) or
when it is the entry point of the analysis.
I'm not sure about where can I notify the checkers of this though. When
is the point when we can say "okay so let's start analyzing this
function"? If you could point me to the method, that would help a lot.
(Ironically, we also have a code comprehension project running where I
work [at Ericsson], but I do not have access to server where we have
the Clang trunk parsed, since I'm doing this from home in my free
time.)
Thanks!
--
Gábor 'ShdNx' Kozár
[4]kozargabor at gmail.com
Email had 1 attachment:
* patch-checkInitialState.diff
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References
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2. mailto:kozargabor at gmail.com
3. mailto:kozargabor at gmail.com
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