[lttng-dev] [PATCH lttng-ust] Fix: Check g++ version before compiling 'hello.cxx' test

[Christian Babeux]

Hi Zifei,

Checking specific version numbers might be a bit counterproductive
(e.g. what if some embedded platform as a GCC 4.7 with designated
initializer explicitly patched out?).

Going forward, I think checking for the designated initializer feature
via a small C++ testfile is more in line with the Autoconf philosophy.
Also, we should conditionally disable the compilation of the
tracepoint probes requiring designated initializers if not supported.

Thanks,

Christian

On Sat, Jun 15, 2013 at 2:08 PM, Zifei Tong <soariez at gmail.com> wrote:
> Designated initializer support that is required to compile c++
> tracepoint probes is only available since g++ 4.7.
>
> Fixes #557
>
> Signed-off-by: Zifei Tong <soariez at gmail.com>
> ---
>  README       |  3 ++-
>  configure.ac | 16 ++++++++++++++--
>  2 files changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/README b/README
> index 1f6b9d2..1c7a2f8 100644
> --- a/README
> +++ b/README
> @@ -111,7 +111,8 @@ USAGE:
>    - Enable instrumentation and control tracing with the "lttng" command
>      from lttng-tools. See lttng-tools doc/quickstart.txt.
>    - Note for C++ support: since LTTng-UST 2.3, both tracepoints and
> -    tracepoint probes can be compiled with g++.
> +    tracepoint probes can be compiled with g++. To compile tracepoint probes
> +    in g++, you need version 4.7 or above.
>
>
>  ENVIRONMENT VARIABLES:
> diff --git a/configure.ac b/configure.ac
> index 802ccaa..85a64a1 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -83,9 +83,21 @@ AC_CACHE_CHECK([whether the C++ compiler works],
>                 [rw_cv_prog_cxx_works],
>                 [AC_LANG_PUSH([C++])
>                 AC_LINK_IFELSE([AC_LANG_PROGRAM([], [])],
> -                               [rw_cv_prog_cxx_works=yes],
> +                               [check_gcc_cxx_version=yes],
>                                 [rw_cv_prog_cxx_works=no])
> -               AC_LANG_POP([C++])])
> +               AC_LANG_POP([C++])
> +               if test "$check_gcc_cxx_version" = "yes"; then
> +                       gcc_cxx_version=`$CXX -dumpversion`
> +                       gcc_cxx_major_version=$(echo $gcc_cxx_version | sed
> 's/^\([[0-9]]*\)\.[[0-9]]*.*$/\1/')
> +                       gcc_cxx_minor_version=$(echo $gcc_cxx_version | sed
> 's/^[[0-9]]*\.\([[0-9]]*\).*$/\1/')
> +                       if test "$gcc_cxx_major_version" -gt 4; then
> +                               rw_cv_prog_cxx_works="yes"
> +                       elif test "$gcc_cxx_major_version" -eq 4 -a
> "$gcc_cxx_minor_version" -ge 7; then
> +                               rw_cv_prog_cxx_works="yes"
> +                       else
> +                               rw_cv_prog_cxx_works="no"
> +                       fi
> +               fi])
>
>  AM_CONDITIONAL([CXX_WORKS], [test "x$rw_cv_prog_cxx_works" = "xyes"])
>
> --
> 1.8.3.1
>
> --
> Best Regards,
> 仝子飞 (Zifei Tong)
>
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