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dnl ----------------------------------------------------------------------

dnl This whole bit snagged from libgomp.

dnl

dnl GCC_LINUX_FUTEX

dnl    (SHELL-CODE_HANDLER)

dnl

AC_DEFUN([GCC_LINUX_FUTEX],[dnl

GCC_ENABLE(linux-futex,default, ,[use the Linux futex system call],

           permit yes|no|default)

case "$target" in

  *-linux*)

    case "$enable_linux_futex" in

      default)

        # If headers don't have gettid/futex syscalls definition, then

        # default to no, otherwise there will be compile time failures.

        # Otherwise, default to yes.  If we don't detect we are

        # compiled/linked against NPTL and not cross-compiling, check

        # if programs are run by default against NPTL and if not, issue

        # a warning.

        enable_linux_futex=no

        AC_LINK_IFELSE(

         [AC_LANG_PROGRAM(

          [#include <sys/syscall.h>

           int lk;],

          [syscall (SYS_gettid); syscall (SYS_futex, &lk, 0, 0, 0);])],

          [save_LIBS="$LIBS"

           LIBS="-lpthread $LIBS"

           AC_LINK_IFELSE(

           [AC_LANG_PROGRAM(

            [#ifndef _GNU_SOURCE

             #define _GNU_SOURCE 1

             #endif

             #include <pthread.h>

             pthread_t th; void *status;],

            [pthread_tryjoin_np (th, &status);])],[enable_linux_futex=yes],

            [if test x$cross_compiling = xno; then

               if getconf GNU_LIBPTHREAD_VERSION 2>/dev/null \

                  | LC_ALL=C grep -i NPTL > /dev/null 2>/dev/null; then :; else

                 AC_MSG_WARN([The kernel might not support futex or gettid syscalls.

If so, please configure with --disable-linux-futex])

               fi

             fi

             enable_linux_futex=yes])

           LIBS="$save_LIBS"])

        ;;

      yes)

        AC_LINK_IFELSE(

         [AC_LANG_PROGRAM(

          [#include <sys/syscall.h>

           int lk;],

          [syscall (SYS_gettid); syscall (SYS_futex, &lk, 0, 0, 0);])],[],

          [AC_MSG_ERROR([SYS_gettid and SYS_futex required for --enable-linux-futex])])

        ;;

    esac

    ;;

  *)

    enable_linux_futex=no

    ;;

esac

if test x$enable_linux_futex = xyes; then

  $1

fi

])