[cfe-dev] C++11 ABI Compatibility and Static Initialization

[Erik Schnetter]

On Apr 7, 2014, at 18:11 , Kevin Locke <kevin at kevinlocke.name> wrote:

> Hello All,
> 
> I've been trying to track down an EXC_BAD_ACCESS error (Bus error: 10)
> which occurs during static initialization when linking a program using
> boost to a library using boost.  The problem occurred, for me, with
> QuantLib, but it has been reported to occur with mlpack[1] and likely
> affects other boost-using libraries as well.  I have determined that
> the issue occurs when a library is compiled with -std=c++11 and the
> program is not (or vice versa).
> 
> Now that I have identified that the issue is C++11 ABI compatibility,
> I can easily avoid the issue on my systems.  However, I have brought
> it to your attention in the hopes that it can either made easier to
> identify or the compatibility can be improved to save future users the
> effort spent debugging to identify the same issue.
> 
> For reference, the issue occurs when using "Apple LLVM version 5.1
> (clang-503.0.38) (based on LLVM 3.4svn)" on Mac OS X 10.9.2 with Boost
> 1.55.0 using the following example program (please excuse the abuse of
> Boost internals to make a minimal test case):
> 
> -8<--libcrash11.cpp---------------------------------------------------
> #include <boost/math/special_functions/lanczos.hpp>
> 
> double libfunc() {
>    return boost::math::lanczos::lanczos17m64::lanczos_sum(1.0);
> }
> -8<--libcrash11.cpp---------------------------------------------------
> 
> -8<--crash11.cpp------------------------------------------------------
> #include <boost/math/special_functions/lanczos.hpp>
> 
> int main(int,char**) {
>    boost::math::lanczos::lanczos17m64::lanczos_sum(1.0);
>    return 0;
> }
> -8<--crash11.cpp------------------------------------------------------
> 
> Compiled as follows:
> clang++ -dynamiclib -o libcrash11.dylib libcrash11.cpp
> clang++ -std=c++11 -L. -lcrash11 -o crash11 crash11.cpp
> 
> Now the binary compiled in C++11 mode has
> double boost::math::lanczos::lanczos17m64::lanczos_sum<double>(double const&)::num
> inside the .__TEXT.__const segment while the other has this symbol inside
> the .__DATA.__data segment.
> 
> Executing crash11 in a debugger shows that the program stops with
> EXC_BAD_ACCESS when attempting to initialize the copy of
> double boost::math::lanczos::lanczos17m64::lanczos_sum<double>(double const&)::num
> inside the crash11.__TEXT.__const segment (which is presumably mapped
> read-only).
> 
> As a non-expert, I would guess that in C++11 the value of the symbol
> can be determined at compile time and placed in the const segment
> while in C++98 mode it must be initialized at runtime and that when
> linked together the initialization is applied to both occurrences of
> the symbol, causing the crash.  But I may be completely off-base with
> this guess.

From my reading of the Boost sources, it seems that Boost determines at compile time whether constexpr is available, and uses it if so. This means that Boost consists of different C++ code depending on whether -std=c++11 is used or not. I would assume that this means that the resulting object code should not be expected to work.

My initial reaction is that this is an error in Boost (which could make this distinction at configuration time instead of at compile time), or that Boost should at least detect this problem and abort with an error. Of course, if clang could detect this incompatibility, this would also be good.

-erik

> So, my question to you is:  Can the situation be improved?  Either by
> avoiding the crash by applying the initialization only to the symbol
> in .__DATA.__data or could it generate a linker or loader error with a
> message that indicates the C++11 ABI as a potential cause of the
> incompatibility?  Or perhaps something else?
> 
> In either case users would be advised to not link different C++
> dialects together.  But I'm afraid we users are perpetually finding
> ways to screw such things up (or, at least, I am).
> 
> Cheers,
> Kevin
> 
> 
> 1.  http://trac.research.cc.gatech.edu/fastlab/ticket/296
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev

-- 
Erik Schnetter <schnetter at gmail.com>
http://www.perimeterinstitute.ca/personal/eschnetter/

My email is as private as my paper mail. I therefore support encrypting
and signing email messages. Get my PGP key from http://pgp.mit.edu/.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 203 bytes
Desc: Message signed with OpenPGP using GPGMail
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20140408/ecae7308/attachment.sig>