llvm dev - Dec 2016 - *********How to get during compile time the base class of casted C++ object inside static_cast<> and dynamic_cast<> and the pointer of the casted object

Hi Mehdi,

thanks a lot for your email. Actually I was disappointed by the fact
that I was not able to get a useful answer to my two questions.
As I observed that the questions move down along the list with time
passing I decided to re-post them in the hope that the questions
will have a better visibility.

Could you help me with the two questions? Finding an expert in this area
would be of great help. Do you think the questions are not well stated.

Regards
  Paul

On 12/21/2016 05:31 PM, Mehdi Amini wrote:
> Hi Paul,
>
> It is the 4th time in two weeks that you repost the exact same two
> emails, that’s a bit high repost rate for the mailing-list, especially
> considering that you already got answers that you ignored previously:
>
> - http://lists.llvm.org/pipermail/llvm-dev/2016-December/108060.html
> - http://lists.llvm.org/pipermail/llvm-dev/2016-December/108051.html
>
> Adding an alternate email in case you didn’t receive previous emails.
> Best,
>
>
> — 
> Mehdi
>
>
>
>
>> On Dec 21, 2016, at 2:47 AM, Paul Muntean via llvm-dev
>> <llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>> wrote:
>>
>> I want to detect bad casts in C++ code by using the Clang
>> compiler. The approach is similar to what Caver and TypeSan do but
>> without using the compiler-rt.
>>
>> Caver and TypeSan:
>>
https://www.usenix.org/system/files/conference/usenixsecurity15/sec15-paper-lee.pdf
>> https://nebelwelt.net/publications/files/16CCS2.pdf
>>
>> For example if I have the following C++ code snippet where I want to
>> cast object b into
>> object D.
>>
>> D* obj = static_cast<D*>(b);
>>
>> from where (inside Clang, LTO, thinLTO, etc.) can I get the base class
>> of D and the base class ob b. Is this
>> available in the Clang compiler or LTO?
>>
>> Also, if b is an object of a virtual Class (class with inherited or its
>> own virtual functions) can I get its virtual pointer at compile time
>> by using the LTO?
>>
>> I found out that in CodeGen/CGExpr.cpp the explicit case
>> "BaseToDerived" is
>> handled and you can retrieve TypeSourceInfo using the function
>> getTypeInfoAsWritten(). It seems that this information is enough to get
>> the exact type of this cast at compile-time and should also work for
>> Template programming, as my, understanding is that Clang should have
>> abstracted the code into, specific types at this point.
>>
>> Am I wrong here?
>>
>> Is there any case where the type of the objects used inside the cast
>> not known at compile time? Can the,
>> 'real' type be hidden behind a pointer?
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
-- 
Paul Muntean
Lehrstuhl für Sicherheit in der Informatik, I20
Prof. Dr. Claudia Eckert
Institut für Informatik TU-München
Boltzmannstr. 3, 85748 Garching, Germany
Tel.: ++49 (89) 289 - 18566
Fax : ++49 (89) 289 - 18579
Room: 01.08.055
E-Mail: paul at sec.in.tum.de 
https://www.sec.in.tum.de

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> On Dec 21, 2016, at 8:38 AM, Paul <paul at sec.in.tum.de> wrote:
> 
> Hi Mehdi,
> 
> thanks a lot for your email. Actually I was disappointed by the fact that I
was not able to get a useful answer to my two questions.
> As I observed that the questions move down along the list with time passing
I decided to re-post them in the hope that the questions
> will have a better visibility.
I don’t think we have a guideline on this, but reposting more than once a week
seems too much.
> Could you help me with the two questions? Finding an expert in this area
would be of great help. Do you think the questions are not well stated.
As mentioned in my previous email, you got two answers to your previous
questions that went apparently ignored. A good starting point would be to
iterate from there. Reposting the same question means that someone may spend
time answering the same thing as the answer you already got because your repost
does not maintain the threading / history of the discussion.

— 
Mehdi


> 
> Regards
>   Paul
> 
> On 12/21/2016 05:31 PM, Mehdi Amini wrote:
>> Hi Paul,
>> 
>> It is the 4th time in two weeks that you repost the exact same two
emails, that’s a bit high repost rate for the mailing-list, especially
considering that you already got answers that you ignored previously:
>> 
>> - 
<http://lists.llvm.org/pipermail/llvm-dev/2016-December/108060.html>http://lists.llvm.org/pipermail/llvm-dev/2016-December/108060.html
<http://lists.llvm.org/pipermail/llvm-dev/2016-December/108060.html>
>> - 
<http://lists.llvm.org/pipermail/llvm-dev/2016-December/108051.html>http://lists.llvm.org/pipermail/llvm-dev/2016-December/108051.html
<http://lists.llvm.org/pipermail/llvm-dev/2016-December/108051.html>
>> 
>> Adding an alternate email in case you didn’t receive previous emails.
>> Best,
>> 
>> — 
>> Mehdi
>> 
>> 
>> 
>> 
>>> On Dec 21, 2016, at 2:47 AM, Paul Muntean via llvm-dev <llvm-dev
at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>>> 
>>> I want to detect bad casts in C++ code by using the Clang
>>> compiler. The approach is similar to what Caver and TypeSan do but
>>> without using the compiler-rt.
>>> 
>>> Caver and TypeSan:
>>>
https://www.usenix.org/system/files/conference/usenixsecurity15/sec15-paper-lee.pdf
<https://www.usenix.org/system/files/conference/usenixsecurity15/sec15-paper-lee.pdf>
>>> https://nebelwelt.net/publications/files/16CCS2.pdf
<https://nebelwelt.net/publications/files/16CCS2.pdf>
>>> 
>>> For example if I have the following C++ code snippet where I want
to
>>> cast object b into
>>> object D.
>>> 
>>> D* obj = static_cast<D*>(b);
>>> 
>>> from where (inside Clang, LTO, thinLTO, etc.) can I get the base
class
>>> of D and the base class ob b. Is this
>>> available in the Clang compiler or LTO?
>>> 
>>> Also, if b is an object of a virtual Class (class with inherited or
its
>>> own virtual functions) can I get its virtual pointer at compile
time
>>> by using the LTO?
>>> 
>>> I found out that in CodeGen/CGExpr.cpp the explicit case
"BaseToDerived" is
>>> handled and you can retrieve TypeSourceInfo using the function
>>> getTypeInfoAsWritten(). It seems that this information is enough to
get
>>> the exact type of this cast at compile-time and should also work
for
>>> Template programming, as my, understanding is that Clang should
have
>>> abstracted the code into, specific types at this point.
>>> 
>>> Am I wrong here?
>>> 
>>> Is there any case where the type of the objects used inside the
cast
>>> not known at compile time? Can the,
>>> 'real' type be hidden behind a pointer?
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
<http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
>> 
> 
> -- 
> Paul Muntean
> Lehrstuhl für Sicherheit in der Informatik, I20
> Prof. Dr. Claudia Eckert
> Institut für Informatik TU-München
> Boltzmannstr. 3, 85748 Garching, Germany
> Tel.: ++49 (89) 289 - 18566
> Fax : ++49 (89) 289 - 18579
> Room: 01.08.055
> E-Mail: paul at sec.in.tum.de <mailto:paul at sec.in.tum.de> 
> https://www.sec.in.tum.de <https://www.sec.in.tum.de/>
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Hi Mehdi,

Ok. I see. I will keep this in mind and agree with your suggestions. I
will try to start a thread from the currently posted questions.

Regards
Paul

On 12/21/2016 05:43 PM, Mehdi Amini wrote:
>
>> On Dec 21, 2016, at 8:38 AM, Paul <paul at sec.in.tum.de
>> <mailto:paul at sec.in.tum.de>> wrote:
>>
>> Hi Mehdi,
>>
>> thanks a lot for your email. Actually I was disappointed by the fact
>> that I was not able to get a useful answer to my two questions.
>> As I observed that the questions move down along the list with time
>> passing I decided to re-post them in the hope that the questions
>> will have a better visibility.
>
> I don’t think we have a guideline on this, but reposting more than
> once a week seems too much.
>
>> Could you help me with the two questions? Finding an expert in this
>> area would be of great help. Do you think the questions are not well
>> stated.
>
> As mentioned in my previous email, you got two answers to your
> previous questions that went apparently ignored. A good starting point
> would be to iterate from there. Reposting the same question means that
> someone may spend time answering the same thing as the answer you
> already got because your repost does not maintain the threading /
> history of the discussion.
>
> — 
> Mehdi
>
>
>
>>
>> Regards
>>   Paul
>>
>> On 12/21/2016 05:31 PM, Mehdi Amini wrote:
>>> Hi Paul,
>>>
>>> It is the 4th time in two weeks that you repost the exact same two
>>> emails, that’s a bit high repost rate for the mailing-list,
>>> especially considering that you already got answers that you
ignored
>>> previously:
>>>
>>> -
http://lists.llvm.org/pipermail/llvm-dev/2016-December/108060.html
>>> -
http://lists.llvm.org/pipermail/llvm-dev/2016-December/108051.html
>>>
>>> Adding an alternate email in case you didn’t receive previous
emails.
>>> Best,
>>>
>>>
>>> — 
>>> Mehdi
>>>
>>>
>>>
>>>
>>>> On Dec 21, 2016, at 2:47 AM, Paul Muntean via llvm-dev
>>>> <llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>> wrote:
>>>>
>>>> I want to detect bad casts in C++ code by using the Clang
>>>> compiler. The approach is similar to what Caver and TypeSan do
but
>>>> without using the compiler-rt.
>>>>
>>>> Caver and TypeSan:
>>>>
https://www.usenix.org/system/files/conference/usenixsecurity15/sec15-paper-lee.pdf
>>>> https://nebelwelt.net/publications/files/16CCS2.pdf
>>>>
>>>> For example if I have the following C++ code snippet where I
want to
>>>> cast object b into
>>>> object D.
>>>>
>>>> D* obj = static_cast<D*>(b);
>>>>
>>>> from where (inside Clang, LTO, thinLTO, etc.) can I get the
base class
>>>> of D and the base class ob b. Is this
>>>> available in the Clang compiler or LTO?
>>>>
>>>> Also, if b is an object of a virtual Class (class with
inherited or its
>>>> own virtual functions) can I get its virtual pointer at compile
time
>>>> by using the LTO?
>>>>
>>>> I found out that in CodeGen/CGExpr.cpp the explicit case
>>>> "BaseToDerived" is
>>>> handled and you can retrieve TypeSourceInfo using the function
>>>> getTypeInfoAsWritten(). It seems that this information is
enough to get
>>>> the exact type of this cast at compile-time and should also
work for
>>>> Template programming, as my, understanding is that Clang should
have
>>>> abstracted the code into, specific types at this point.
>>>>
>>>> Am I wrong here?
>>>>
>>>> Is there any case where the type of the objects used inside the
cast
>>>> not known at compile time? Can the,
>>>> 'real' type be hidden behind a pointer?
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>
>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>
>> -- 
>> Paul Muntean
>> Lehrstuhl für Sicherheit in der Informatik, I20
>> Prof. Dr. Claudia Eckert
>> Institut für Informatik TU-München
>> Boltzmannstr. 3, 85748 Garching, Germany
>> Tel.: ++49 (89) 289 - 18566
>> Fax : ++49 (89) 289 - 18579
>> Room: 01.08.055
>> E-Mail: paul at sec.in.tum.de 
>> https://www.sec.in.tum.de
>
-- 
Viele Grüße,
Paul Muntean
Lehrstuhl für Sicherheit in der Informatik, I20
Prof. Dr. Claudia Eckert
Institut für Informatik TU-München
Boltzmannstr. 3, 85748 Garching, Germany
Tel.: ++49 (89) 289 - 18566
Fax : ++49 (89) 289 - 18579
Room: 01.08.055
E-Mail: paul at sec.in.tum.de 
https://www.sec.in.tum.de

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On Wed, Dec 21, 2016 at 05:38:58PM +0100, Paul via llvm-dev
wrote:
> thanks a lot for your email. Actually I was disappointed by the fact
> that I was not able to get a useful answer to my two questions.
> As I observed that the questions move down along the list with time
> passing I decided to re-post them in the hope that the questions
> will have a better visibility.
If the answers don't match your expected direction, it is often a sign
that your question was misunderstood and needs clarification. A good
starting point would be to reply to your original mail and restate the
question or add more context.

Joerg