[cfe-commits] unix.Malloc static checker improvement: memory.LeakPtrValChanged

[Branden Archer]

Anna,

Thanks for committing these!

Who should I contact to have the LeakPtrValChanged section of the following
page updated/removed, as the checker is now in?
http://clang-analyzer.llvm.org/potential_checkers.html

- Branden

On Thu, Feb 7, 2013 at 6:09 PM, Anna Zaks <ganna at apple.com> wrote:

> Branden,
>
> Thanks for working on this and polishing it up! I've committed the changes
> in r174677 and r 174678.
>
> I had to change the tests from the first patch slightly since we've made
> analyzer more pessimistic as a quick fix to a regression in r174468. This
> resulted in the expected leaks not being reported.
>
> Cheers,
> Anna.
> On Feb 3, 2013, at 8:10 PM, Branden Archer <b.m.archer4 at gmail.com> wrote:
>
> Here is the commit message for the first patch:
> [analyzer] Pass pointer escape type to checkPointerEscape checker
>
> The checkPointerEscape checker previously did not specify how a
> pointer escaped. This change includes an enum which describes the
> different ways a pointer may escape. This enum is passed to the
> checkPointerEscape checker when a pointer escapes. If the escape
> is due to a function call, the call is passed. This changes
> previous behavior where the call is passed as NULL if the escape
> was due to indirectly invalidating the region the pointer referenced.
>
> Here is the commit message for the second patch:
> [analyzer] malloc checker reports bugs when freeing memory with offset
> pointer
>
> The malloc checker will now catch the case when a previously malloc'ed
> region is freed, but the pointer passed to free does not point to the
> start of the allocated memory. For example:
>
> int *p1 = malloc(sizeof(int));
> p1++;
> free(p1); // warn
>
> From the "memory.LeakPtrValChanged enhancement to unix.Malloc" entry
> in the list of potential checkers.
>
>
> What I meant is that the tests should not pass before the patch is
>> applied. Then, after you apply the patch, the tests should start passing.
>>
>
> Thanks for the reminder. The other tests for the second patch checked out,
> but what I was trying for the first patch was not. I decided to take a more
> direct approach to testing the first patch. Instead of trying to figure out
> a system header function that would take a struct containing a pointer (or
> for the simple stream checker, a FILE pointer), I decided to 'create my
> own' by adding a fake system header function in the header included in the
> test files. In doing so, I can easily see that previous to the change there
> was a false negative, but after the change a bug was found.
>
> - Branden
>
> On Fri, Feb 1, 2013 at 1:20 PM, Anna Zaks <ganna at apple.com> wrote:
>
>>
>> On Jan 31, 2013, at 7:20 PM, Branden Archer <b.m.archer4 at gmail.com>
>> wrote:
>>
>> Oh, one other thing. I do not know who does the committing when the patch
>> is approved. Should I prove a patch that has my commit message in it and
>> username? Would either of you be pushing the change, or would I be pushing
>> it?
>>
>>
>> One of us will push this and mention that the patch is by you in the
>> commit message. Please do send the commit message!
>>
>> Also, thanks for your comments and discussion on this patch, and for
>> keeping with it for so long! I appreciate your feedback and the opportunity
>> to learn some about the static analyzer of clang.
>>
>> - Branden
>>
>> On Thu, Jan 31, 2013 at 10:10 PM, Branden Archer <b.m.archer4 at gmail.com>wrote:
>>
>>> Have you double checked that the tests did not generate the warnings
>>>> before the patch?
>>>>
>>>
>>> When you mentioned this, I had a moment of doubt. I checked for compiler
>>> warnings and the 'make test' before I emailed my patches, and all came back
>>> clean. Just to be sure I updated my source and compiled again, all still
>>> clean. Did you see something in particular, or just wanted to make sure?
>>>
>>>
>> What I meant is that the tests should not pass before the patch is
>> applied. Then, after you apply the patch, the tests should start passing.
>>
>>
>>> +void testPassConstPointerIndirectly() {
>>>> +  struct HasPtr hp;
>>>> +  hp.p = fopen("myfile.txt", "w");
>>>> +  fputc(0, (FILE *)&hp);
>>>> +  return; // expected-warning {{Opened file is never closed; potential
>>>> resource leak}}
>>>> +}
>>>>
>>>> Heh. Did you really want this test case? It's not actually valid (&hp
>>>> is a FILE**, not a FILE*):
>>>>
>>>
>>> I knew the test was not proper code, but it was the only way I could
>>> think of to pass a structure to a known library function that was known to
>>> not close a file. I replaced it in the attached patches with passing the
>>> HasPtr structure to a function that accepts it as a const parameter. I am
>>> not sure this still tests the same thing (as I do not fully appreciate how
>>> the analyzer knows that a function will not close the stream. I am hoping
>>> that if the parameter is passed as a const that it will assume this).
>>>
>>> - Branden
>>>
>>>
>>> On Thu, Jan 31, 2013 at 8:26 PM, Jordan Rose <jordan_rose at apple.com>wrote:
>>>
>>>>
>>>> On Jan 31, 2013, at 5:21 , Branden Archer <b.m.archer4 at gmail.com>
>>>> wrote:
>>>>
>>>> Basically, you need to pass a pointer which we are tracking to a
>>>>> function call indirectly (ex: as a field in a struct..). You should pass it
>>>>> to a function which is known not to free memory or close stream. Finally,
>>>>> you leak that resource/pointer.
>>>>>
>>>>> Previously, we would have a false negative - no leak would be
>>>>> reported. Now, we should be catching the leak.
>>>>>
>>>>
>>>> Ah, got you. See the first attached patch for these added cases.
>>>>
>>>> - Branden
>>>>
>>>>
>>>> +void testPassConstPointerIndirectly() {
>>>> +  struct HasPtr hp;
>>>> +  hp.p = fopen("myfile.txt", "w");
>>>> +  fputc(0, (FILE *)&hp);
>>>> +  return; // expected-warning {{Opened file is never closed; potential
>>>> resource leak}}
>>>> +}
>>>>
>>>> Heh. Did you really want this test case? It's not actually valid (&hp
>>>> is a FILE**, not a FILE*):
>>>>
>>>>
>>>> A few remaining comments for the MallocChecker patch:
>>>>
>>>> +  if (ExplodedNode *N = C.generateSink()) {
>>>>
>>>> Please use an early return here.
>>>>
>>>>
>>>> +    int offsetBytes =
>>>> Offset.getOffset()/C.getASTContext().getCharWidth();
>>>>
>>>> *Very* nitpicky, but can you put spaces around the /?
>>>>
>>>>
>>>> +       << ((abs(offsetBytes) > 1) ? "bytes" : "byte")
>>>>
>>>> Perfect!
>>>>
>>>> Jordan
>>>>
>>>
>>>
>>
>>
> <01-modify-checkPointerEscape.patch><02-update-malloc-checker.patch>
>
>
>
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