[PATCH v2] [RTEMS] Always use atomic builtins for libstdc++

Sebastian Huber sebastian.huber at embedded-brains.de
Thu Sep 22 13:32:19 UTC 2016


On 22/09/16 15:25, Joel Sherrill wrote:
> /The target pattern in the commit message doesn't look right.
> It should be *-*-rtems* I think.

It should be ok since host_os is used:

# It uses the following shell variables as set by config.guess:
#   host                The configuration host (full CPU-vendor-OS triplet)
#   host_cpu            The configuration host CPU
#   host_os             The configuration host OS

>
> Do all BSPs for m68k build with C++ enabled?

Yes, but I face currently some other problems with GCC 7:

https://gcc.gnu.org/ml/gcc/2016-09/msg00114.html

There is also a NULL pointer access in wctob() with the latest Newlib.

>
> What code is used for atomic operations on say a 68000 or
> 68020?

They use the libatomic if the atomic operations are not supported by 
hardware. libatomic uses _Libatomic_Protect_start() and 
_Libatomic_Protect_end() on RTEMS.

>
> Thanks.
>
> --joel
>
> On Thu, Sep 22, 2016 at 3:47 AM, Sebastian Huber 
> <sebastian.huber at embedded-brains.de 
> <mailto:sebastian.huber at embedded-brains.de>> wrote:
>
>     v2: Fix shell script part since shell grouping is expressed by { }.
>
>     libstdc++-v3/
>             * config/cpu/m68k/atomicity.h: Adjust comment.
>             * acinclude.m4 (GLIBCXX_ENABLE_ATOMIC_BUILTINS): Honor
>             explicit atomicity_dir setup via configure.host.
>             * configure.host (rtems-*): Set atomicity_dir.
>             * configure: Regenerate.
>     ---
>      libstdc++-v3/acinclude.m4                |  5 +++--
>      libstdc++-v3/config/cpu/m68k/atomicity.h |  3 +++
>      libstdc++-v3/configure                   | 11 ++++++-----
>      libstdc++-v3/configure.host              |  4 ++++
>      4 files changed, 16 insertions(+), 7 deletions(-)
>
>     diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
>     index 6d897be..d7db435 100644
>     --- a/libstdc++-v3/acinclude.m4
>     +++ b/libstdc++-v3/acinclude.m4
>     @@ -3490,9 +3490,10 @@ EOF
>        AC_LANG_RESTORE
>
>        # Set atomicity_dir to builtins if all but the long long test
>     above passes.
>     -  if test "$glibcxx_cv_atomic_bool" = yes \
>     +  if { test "$glibcxx_cv_atomic_bool" = yes \
>           && test "$glibcxx_cv_atomic_short" = yes \
>     -     && test "$glibcxx_cv_atomic_int" = yes; then
>     +     && test "$glibcxx_cv_atomic_int" = yes } \
>     +     || test "$atomicity_dir" = "cpu/generic/atomicity_builtins";
>     then
>          AC_DEFINE(_GLIBCXX_ATOMIC_BUILTINS, 1,
>          [Define if the compiler supports C++11 atomics.])
>          atomicity_dir=cpu/generic/atomicity_builtins
>     diff --git a/libstdc++-v3/config/cpu/m68k/atomicity.h
>     b/libstdc++-v3/config/cpu/m68k/atomicity.h
>     index f421330..a9ddc6b 100644
>     --- a/libstdc++-v3/config/cpu/m68k/atomicity.h
>     +++ b/libstdc++-v3/config/cpu/m68k/atomicity.h
>     @@ -48,6 +48,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>        }
>
>      #elif defined(__rtems__)
>     +  // This code is only provided for reference.  RTEMS uses now
>     the atomic
>     +  // builtins and libatomic.  See configure.host.
>     +  //
>        // TAS/JBNE is unsafe on systems with strict priority-based
>     scheduling.
>        // Disable interrupts, which we can do only from supervisor mode.
>        _Atomic_word
>     diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
>     index 6332c4d..d09a7e0 100755
>     --- a/libstdc++-v3/configure
>     +++ b/libstdc++-v3/configure
>     @@ -15539,9 +15539,10 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
>
>
>        # Set atomicity_dir to builtins if all but the long long test
>     above passes.
>     -  if test "$glibcxx_cv_atomic_bool" = yes \
>     +  if { test "$glibcxx_cv_atomic_bool" = yes \
>           && test "$glibcxx_cv_atomic_short" = yes \
>     -     && test "$glibcxx_cv_atomic_int" = yes; then
>     +     && test "$glibcxx_cv_atomic_int" = yes } \
>     +     || test "$atomicity_dir" = "cpu/generic/atomicity_builtins";
>     then
>
>      $as_echo "#define _GLIBCXX_ATOMIC_BUILTINS 1" >>confdefs.h
>
>     @@ -15573,7 +15574,7 @@ $as_echo "$as_me: WARNING: Performance of
>     certain classes will degrade as a resu
>        # unnecessary for this test.
>
>          cat > conftest.$ac_ext << EOF
>     -#line 15576 "configure"
>     +#line 15577 "configure"
>      int main()
>      {
>        _Decimal32 d1;
>     @@ -15615,7 +15616,7 @@ ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
>        # unnecessary for this test.
>
>          cat > conftest.$ac_ext << EOF
>     -#line 15618 "configure"
>     +#line 15619 "configure"
>      template<typename T1, typename T2>
>        struct same
>        { typedef T2 type; };
>     @@ -15649,7 +15650,7 @@ $as_echo "$enable_int128" >&6; }
>          rm -f conftest*
>
>          cat > conftest.$ac_ext << EOF
>     -#line 15652 "configure"
>     +#line 15653 "configure"
>      template<typename T1, typename T2>
>        struct same
>        { typedef T2 type; };
>     diff --git a/libstdc++-v3/configure.host b/libstdc++-v3/configure.host
>     index c0cc3ee..eb56ab1 100644
>     --- a/libstdc++-v3/configure.host
>     +++ b/libstdc++-v3/configure.host
>     @@ -296,6 +296,10 @@ case "${host_os}" in
>          os_include_dir="os/qnx/qnx6.1"
>          c_model=c
>          ;;
>     +  rtems*)
>     +    # Use libatomic if necessary and avoid libstdc++ specific
>     atomicity support
>     +    atomicity_dir="cpu/generic/atomicity_builtins"
>     +    ;;
>        solaris2)
>          # This too-vague configuration does not provide enough
>     information
>          # to select a ctype include, and thus os_include_dir is a
>     crap shoot.
>     --
>     1.8.4.5
>
>     _______________________________________________
>     devel mailing list
>     devel at rtems.org <mailto:devel at rtems.org>
>     http://lists.rtems.org/mailman/listinfo/devel
>     <http://lists.rtems.org/mailman/listinfo/devel>
>
>

-- 
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber at embedded-brains.de
PGP     : Public key available on request.

Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.




More information about the devel mailing list