Re: [2/2] Add AddressSanitizer annotations to std::string.

[Mikhail Kashkarov <m dot kashkarov at partner dot samsung dot com>]

^^ gentle ping.

On 07/16/2018 07:16 PM, Mikhail Kashkarov wrote:
> Rebased and update patch (typos, add missing annotations),
> add ASan teststo verify string annotation.
>
>
> On 06/28/2018 11:09 AM, Mikhail Kashkarov wrote:
>> ^ gentle ping.
>>
>>
>> On 06/08/2018 05:54 PM, Mikhail Kashkarov wrote:
>>> Hello,
>>>
>>> I've updated patches for std::string sanitization and disabling CXX11
>>> string SSO usage for correct sanitization.
>>>
>>>    >>       _M_destroy(_M_allocated_capacity);
>>>    >>+        else
>>>    >>+      __annotate_delete();
>>>    >
>>>    >Do these calls definitely optimize away completely when not
>>>    >sanitizing? Even for -O1, -Os and -Og?
>>>    >
>>>    >For std::vector annotation I used macros to add these 
>>> annotations, so
>>>    >there is no change to the generated code when annotations are
>>>    >disabled. But it makes the code quite ugly.
>>>
>>> I've checked asm code for string-inst.o and it looks like this calls 
>>> are
>>> optimized away, but there are some light changes after patch fir .
>>>
>>>    > Right, I was wondering specifically about the <fstream>
>>>    > instantiations. I could be wrong but I don't think anything in
>>>    > <fstream> creates, destroys or modifies a std::basic_string.
>>>
>>> I was confused by reinterpret_cast's on strings in fstream.tcc, looks
>>> like this is not needed, you are right.
>>>
>>>    >>       // calling 4.0.x+ _S_create.
>>>    >>       __p->_M_set_sharable();
>>>    >>+#if _GLIBCXX_SANITIZER_ANNOTATE_STRING
>>>    >>+      __p->_M_length = 0;
>>>    >>+#endif
>>>    >
>>>    > Why is this needed? I think a comment explaining it would help 
>>> (like
>>>    > the one above explaining why calling _M_set_sharable() is needed).
>>>
>>> Checked current version without this change, looks like now it works,
>>> reverted.
>>>
>>> Short summary:
>>> The reason for changing strings layout under sanitization is to 
>>> place string
>>> char buffer on heap for correct aligning in 32-bit environments,
>>> both pre-CXX11 and CXX11 strings ABI.
>>>
>>> | Sanitize string | string type | ABI is changed? | 32-bit | 64-bit |
>>> |-----------------+-------------+-----------------+--------+--------|
>>> | FULL            | SSO-string  | yes             | +      | +      |
>>> |                 | COW-string  | yes             | +      | +      |
>>> |-----------------+-------------+-----------------+--------+--------|
>>> | PARTIAL         | SSO-string  | no              | -+(*)  | +      |
>>> |                 | COW-string  | no              | -      | +      |
>>> *only longs strings are sanitized for 32-bit
>>>
>>> Some functions with new define looks a bit messy without changing 
>>> internal
>>> functions(operator=), I'm also not sure if disabling string SSO 
>>> usage define
>>> should also affects other parts that relies on basic_string class size
>>> (checks
>>> with static_assert in exceptions/shim-facets).
>>>
>>>
>>> Any thoughts?
>>>
>>> On 05/29/2018 06:55 PM, Jonathan Wakely wrote:
>>>> On 29/05/18 18:18 +0300, Kashkarov Mikhail wrote:
>>>>> Jonathan Wakely <jwakely@redhat.com> writes:
>>>>>>> --- a/libstdc++-v3/include/bits/fstream.tcc
>>>>>>> +++ b/libstdc++-v3/include/bits/fstream.tcc
>>>>>>> @@ -1081,6 +1081,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>>>>>
>>>>>>>     // Inhibit implicit instantiations for required instantiations,
>>>>>>>     // which are defined via explicit instantiations elsewhere.
>>>>>>> +#if !_GLIBCXX_SANITIZE_STRING
>>>>>>> #if _GLIBCXX_EXTERN_TEMPLATE
>>>>>>>     extern template class basic_filebuf<char>;
>>>>>>>     extern template class basic_ifstream<char>;
>>>>>>> @@ -1094,6 +1095,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>>>>>     extern template class basic_fstream<wchar_t>;
>>>>>>> #endif
>>>>>>> #endif
>>>>>>> +#endif // !_GLIBCXX_SANITIZE_STRING
>>>>>> Why do we need to disable these explicit instantiation declarations?
>>>>>> Are they affected by the std::string layout changes? Is that just
>>>>>> because of the constructors taking std::string, or something else?
>>>>> Libstdc++ build is not sanitized, so macroses that requires
>>>>> AddressSanitizer support will not applied and these templates will be
>>>>> instantate without support for ASan annotations.
>>>> Right, I was wondering specifically about the <fstream>
>>>> instantiations. I could be wrong but I don't think anything in
>>>> <fstream> creates, destroys or modifies a std::basic_string.
>>>>
>>>>
>>>>
>>>>
>>>>
>

-- 
Best regards,
Kashkarov Mikhail
Samsung R&D Institute Russia