[PATCH][Review request] unix.Malloc checker improvement: +handling new/delete, +memory.MismatchedFree, +memory.MismatchedDelete, +improved display names for allocators/deallocators

[Anna Zaks]

On Feb 21, 2013, at 6:26 PM, Anna Zaks <ganna at apple.com> wrote:

> 
> On Feb 21, 2013, at 6:00 PM, Anton Yartsev <anton.yartsev at gmail.com> wrote:
> 
>>> 
>>> On Feb 19, 2013, at 10:18 PM, Anton Yartsev <anton.yartsev at gmail.com> wrote:
>>> 
>>>> Hi, Jordan. Thanx for the review!
>>>> 
>>>> Attached is the new version of the patch with all the comments addressed. Also added support for directly called operator new()/new[]() and operator delete()
>>>> 
>>>> There is currently one problem with handling of operator delete(). The following test
>>>> 
>>>> void testDeleteOp1() {
>>>>  int *p = (int *)malloc(sizeof(int));
>>>>  operator delete(p); // FIXME: should complain "Argument to operator delete() was allocated by malloc(), not operator new"
>>>> }
>>>> 
>>>> produce no warnings as attached RefState seem to be missing at the point when checkPostStmt(const CallExpr *CE, CheckerContext &C) callback is called for operator delete(p).
>>>> I haven't investigated the problem deeply yet, intend to address it parallel with the review.
>>>> 
>>>>> +  if (NE->getNumPlacementArgs())
>>>>> +    return;
>>>>> +  // skip placement new operators as they may not allocate memory
>>>>> 
>>>>> Two comments here:
>>>>> - Please make sure all comments are complete, capitalized, and punctuated sentences. (This has the important one, "complete"....just missing capitalization and punctuation.)
>>>> I'll try. Unfortunately I am not as good in English as I want to be, so sorry for my grammar, syntax, and punctuation.
>>>> 
>>>> -- 
>>>> Anton
>>>> 
>>>> <MallocChecker_v2.patch>
>>> 
>> 
>> Hi Anna. Thanks for your comments! Attached is the new patch.
>> 
>>> Just adding another kind as extra enumeration values does not seem right. Another option is to make Kind be a pointer to a static array, which contains objects recording all necessary info about each kind (MacOSKeychainAPIChecker uses this approach). This is probably an overkill for now, but is another option.
>> Not sure that I have got an idea.
>> The memory and deallocator kind are both set for a RefState. Do you mean creating a static array with 'memory kinds' * 'deallocator kind' elements for all possible combinations? Also there is no necessary info other then the kind itself.
>> Left for now.
> 
> I think of ToBeReleasedWith* as being different types of Allocate; I don't think they should be separate values in the same enum. It's also unfortunate to have to copy the constant values in both places - DeallocatorKind and RefState::Kind. Maybe you could restructure this similarly to how this is done in SVals.h?
> 
>> 
>>> +  const FunctionDecl *getCalleeDecl() const { return CalleeDecl; }
>>> Do we only store the name of the allocator declaration here?
> 
> If the Decl is always an allocator Decl, we should change the name of the method to be more descriptive.
>>> Do we need to store this in the state? (Growing states implies memory overhead.) Can't this be easily implied from the kind?
>> Kind can't give us information about the name of an allocator that can be malloc(), realloc(), a user function with ownership_takes attribute, etc.
>> One solution to avoid keeping a CalleeDecl in RefState is to rollback to CallExpr::getDirectCallee() from CheckerContext::getCalleeDec() and to print "malloc()" in case of indirect calls.
> 
> Ok, I see.

After thinking about it some more, I do not think we should add an extra pointer to the state to differentiate between few allocator functions. In the case when we do not have ownership attributes, we only have few possible allocators, whose names we know ahead of time. In case we support ownership attributes, we are likely to have few allocator functions whose names we could just store in the checker state on the first encounter (like we store the IdentifierInfo).  

In addition, we could change the ownership attributes in such a way that each allocator would have a corresponding deallocator; for example, if we wanted to check matching allocators and deallocators. Annotated deallocators won't necessarily be one of the functions you know at compile time, so the DeallocatorKind enum would not cover it. I think, it's best if we kept a table on a side that would store this info (allocation function name, deallocator) and refer to the entries in the table from the state. (Take a look at MacOSKeychainAPIChecker - it's very similar to malloc, but it handles different allocator/deallocator pairs. I think a similar solution could work in this case as well. Other solutions that address these issues are welcome as well!)

>> Jordan, what do you think about this?
>> 
>>> +void MallocChecker::checkPostStmt(const CXXNewExpr *NE, 
>>> +                                  CheckerContext &C) const {NE
>>> +
>>> +  FunctionDecl *OperatorNew = NE->getOperatorNew();
>>> +  if (!OperatorNew)
>>> +    return;
>>> +
>>> +  // Skip custom new operators
>>> +  if (!OperatorNew->isImplicit() &&
>>> +      !C.getSourceManager().isInSystemHeader(OperatorNew->getLocStart()) &&
>>> +      !NE->isGlobalNew())
>>> +    return;
>>> +
>>> +  // Skip standard global placement operator new/new[](std::size_t, void * p);
>>> +  // process all other standard new/new[] operators including placement
>>> +  // operators new/new[](std::size_t, const std::nothrow_t&)
>>> +  if (OperatorNew->isReservedGlobalPlacementOperator())
>>> +    return;
>>> 
>>> Is there a reason why we first process each operator new in "checkPostStmt(const callExpr" and finish processing in "checkPostStmt(const CXXNewExpr" ? I think the code would be simpler if everything could be done in a single callback. 
>> Code added to "checkPostStmt(const callExpr" is for processing direct calls to operator new/delete functions, "checkPostStmt(const CXXNewExpr" is for handling new expressions. Either first or second callback is called in each particular case but not both of them. Am I right?
>> 
> 
> I see; makes sense. Please, add a comment in "checkPostStmt(const callExpr*".
> 
>>> 
>>> +void MallocChecker::PrintExpectedAllocName(raw_ostream &os, CheckerContext &C, 
>>> +                                           const Expr *E) const {
>>> +  DeallocatorKind dKind = GetDeallocKind(C, E);
>>> +
>>> +  switch(dKind) {
>>> +    case D_free: os << "malloc()"; return;
>>> +    case D_delete: os << "operator new"; return;
>>> +    case D_deleteArray: os << "operator new[]"; return;
>>> +    case D_unknown: os << "unknown means"; return;
>>> 
>>> This function is used to form user visible warnings. Do we ever expect it to print "unknown means"? Can this be based on the Kind stored inside of RefState, where there is no D_unknown?
>> Right, changed the case to assert. There is actually implicit D_unknown in RefState - case when 2nd and 3rd bits are set to zero.
>> 
>> -- 
>> Anton
>> <MallocChecker_v3.patch>
> 
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