std::exception_ptr on Cygwin

std::exception_ptr on Cygwin

[Piotr Wyderski]

It is impossible to use std::exception_ptr and related
functionality on Cygwin in C++0x mode, despite the
fact the necessary classes seem to be implemented.
That is because in <exception> there is a conditional
block:

#if (defined(__GXX_EXPERIMENTAL_CXX0X__) \
     && defined(_GLIBCXX_ATOMIC_BUILTINS_4))
#include <exception_ptr.h>
#endif

The macro __GXX_EXPERIMENTAL_CXX0X__ is
defined correctly, as expected, but

_GLIBCXX_ATOMIC_BUILTINS_4

is not, as Cygwin does not use glibc. Its underlying
processor architecture, however, supports the fullest
set of atomic primitives, so is there really a need to
make it glibc-dependent? If I enforce the macro
definition from the command line, then the exception_ptr
-dependent code compiles correctly (but does not link
because of

 undefined reference to `std::__exception_ptr::exception_ptr::~exception_ptr()

and the other non-inline members. I presume
it is not the recommended way.

Best regards
Piotr Wyderski

Re: std::exception_ptr on Cygwin

[Andrew Pinski]

On Thu, May 28, 2009 at 4:00 PM, Piotr Wyderski
<piotr.wyderski@gmail.com> wrote:
> is not, as Cygwin does not use glibc. Its underlying
> processor architecture, however, supports the fullest
> set of atomic primitives, so is there really a need to
> make it glibc-dependent? If I enforce the macro
> definition from the command line, then the exception_ptr
> -dependent code compiles correctly (but does not link
> because of

Actually it is not due not to glibc but the default for i686-linux-gnu
and i686-cygwin is really targeting 386 and tuning for generic cpu.
i386 did not have atomic locks at all but 486 and above does.  This
has come up many times in the past too.

-- Pinski

Re: std::exception_ptr on Cygwin

[Piotr Wyderski]

Andrew Pinski wrote:

> i386 did not have atomic locks at all but 486 and above does.

Thanks, now it is obvious to me. So how should
I configure my GCC-trunk build? It seems that
--with-cpu is not enough:

$ gcc -v
Using built-in specs.
Target: i686-pc-cygwin
Configured with: ../configure --prefix=/opt/gcc-4.5-trunk -v --enable-bootstrap
--enable-version-specific-runtime-libs --enable-static --enable-shared --enable-
shared-libgcc --with-gnu-ld --with-gnu-as --enable-sjlj-exceptions --enable-lang
uages=c,c++ --disable-symvers --enable-libjava --disable-nls --with-cpu=core2 --
enable-threads=posix

Best regards
Piotr Wyderski

Re: std::exception_ptr on Cygwin

[Dave Korn]

Piotr Wyderski wrote:
> Andrew Pinski wrote:
> 
>> i386 did not have atomic locks at all but 486 and above does.
> 
> Thanks, now it is obvious to me. So how should
> I configure my GCC-trunk build? It seems that
> --with-cpu is not enough:

  You need to look closer at the definition of -mcpu, -mtune and -march.  It's
the arch that selects which instructions may be generated, not the tune/cpu
setting which just controls scheduling optimisation and selection of best
instructions between equally available alternatives.  I use "--with-arch=i686
--with-tune=generic".

    cheers,
      DaveK