This reminds me
https://code.google.com/p/address-sanitizer/issues/detail?id=258
(and also reminds me that I hate exceptions :)
The situation you describe (and my test shows) may lead only to false
negatives (missed bugs),
and not to false positives or crashes (the checks in
__sanitizer_annotate_contiguous_container are disabled due to the above
bug).
At least I don't see how these may happen.
Of course, __sanitizer_verify_contiguous_container will fail on such test,
but that's a test-only routine anyway.
We may eventually fix the problem with RAII, as you suggested, but maybe
it's ok to keep the code as is for a while.
Marshall, your thoughts?
--kcc
On Mon, May 12, 2014 at 8:35 PM, Kostya Serebryany <k...@google.com> wrote:
>
>
>
> On Mon, May 12, 2014 at 7:04 PM, Stephan Tolksdorf <s...@quanttec.com>wrote:
>
>> On 14-05-12 16:27, Kostya Serebryany wrote:
>> > And an unrelated issue: the documentation for
>> > __sanitizer_annotate_contiguous_container states that the
>> > complete buffer should be unpoisened before it is deallocated.
>> > This doesn't seem to be happening in the destructor or in the
>> > deallocate function.
>> >
>> > Here we rely on the fact that vector is using the default allocator,
>> > which immediately calls delete, which itself unpoisons the memory
>> > chunk.
>>
>> Do I understand you correctly, that the global ::operator delete doesn't
>> actually require the complete buffer to be unpoisened? I assume this is
>> also true for ::free then?
>>
>>
>> Reproduced. (we have very little code with exceptions so this has
>>> avoided our testing efforts :)
>>> Any suggestion for the fix?
>>>
>>
>> Using a scope guard object for annotating operations that increase the
>> size would be one possibility, as e.g. in the following pseudo code:
>>
>
> OMG. Yes, I can see how it works, although it looks so heavy. Let me (and
> others) think a bit.
>
>
>>
>> struct AnnotatedAppendScope {
>> Vector& v;
>> const size_t newLength;
>> #if USE_ASAN
>> bool committed;
>> #endif
>>
>> /// \pre vector.length() < newLength <= vector.capacity()
>> AnnotatedAppendScope(Vector& vector, size_t newLength)
>> : v(vector), newLength(newLength)
>> #if USE_ASAN
>> , committed(false)
>> #endif
>> {
>> #if USE_ASAN
>> __sanitizer_annotate_contiguous_container(
>> v.begin(), v.begin() + v.capacity(),
>> v.begin() + v.length(), v.begin() + newLength;
>> );
>> #endif
>> }
>>
>> #if USE_ASAN
>> ~AnnotatedAppendScope() {
>> if (!committed) {
>> __sanitizer_annotate_contiguous_container(
>> v.begin(), v.begin() + v.capacity(),
>> v.begin() + newLength, v.begin() + v.length();
>> );
>> }
>> }
>> #endif
>>
>> void commitLength() {
>> v.setLength(newLength);
>> #if USE_ASAN
>> committed = true;
>> #endif
>> }
>> };
>>
>> void Vector::push_back(const T& value) {
>> reserve(length() + 1);
>> AnnotatedAppendScope scope(*this, length() + 1);
>> new (end()) T(value);
>> scope.commitLength();
>> }
>>
>> There's another comment below.
>>
>>
>>
>>> #include <vector>
>>> #include <assert.h>
>>> #include <iostream>
>>> #include <sanitizer/asan_interface.h>
>>> using namespace std;
>>>
>>> class X {
>>> public:
>>> X(const X &x) {
>>> if (x.a == 42) throw 0;
>>> a = x.a;
>>> }
>>> X(char arg): a(arg){}
>>> char get() const { return a; }
>>> private:
>>> char a;
>>> };
>>>
>>> int main() {
>>> vector<X> v;
>>> v.reserve(2);
>>> v.push_back(X(2));
>>> assert(v.size() == 1);
>>> try {
>>> v.push_back(X(42));
>>> assert(0);
>>> } catch (int e) {
>>> assert(v.size() == 1);
>>> }
>>> assert(v.size() == 1);
>>> assert(v[1].get() != 777);
>>>
>>
>> What does the above line test?
>> It would always fail if the index is assert checked, which currently is
>> the case when _LIBCPP_DEBUG is defined.
>
>
> I just wanted to verify that asan does not catch the bug. This line is
> indeed redundant.
>
>
>>
>>
>> char *p = (char*)v.data();
>>> assert(!__asan_address_is_poisoned(p));
>>> assert(__asan_address_is_poisoned(p+1));
>>> }
>>>
>>>
>> - Stephan
>>
>>
>
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