+AC_SUBST(SUBARCHTYPE)
+
+[
+#if test "x$ARCHTYPE" = "xx86" -a "x$host_cpu" != "xi386" -a "x$host_cpu" != "xi486" -a "x$host_cpu" != "xi586"; then
+#For now, using lock; addl compatibility mode even for i686, because the
+#Pentium III is seen as a i686, but lacks mfence instruction.
+#Only using fence for x86_64.
+if test "x$ARCHTYPE" = "xx86" -a "x$host_cpu" != "xi386" -a "x$host_cpu" != "xi486" -a "x$host_cpu" != "xi586" -a "x$host_cpu" != "xi686"; then
+]
+ AC_DEFINE([CONFIG_RCU_HAVE_FENCE], [1])
+[
+fi
+]
+
+AC_MSG_CHECKING([sys_futex()])
+AC_TRY_COMPILE(
+[
+#include <sys/syscall.h>
+],
+[
+#ifndef __NR_futex
+#error "futexes not available"
+#endif
+],
+[
+ AC_MSG_RESULT([yes])
+ AC_DEFINE([CONFIG_RCU_HAVE_FUTEX], [1])
+ compat_futex_test=0
+]
+,
+[
+ AC_MSG_RESULT([no])
+ compat_futex_test=1
+]
+)
+
+AM_CONDITIONAL([COMPAT_FUTEX], [ test "x$compat_futex_test" = "x1" ])
+
+AM_CONDITIONAL([GCC_API], [test "x$ARCHTYPE" != xx86 -a "x$ARCHTYPE" != xppc])
+
+AM_CONDITIONAL([COMPAT_ARCH], [test "x$SUBARCHTYPE" = xx86compat ])
+
+[
+if test "x$SUBARCHTYPE" = xx86compat; then
+]
+ AC_DEFINE([CONFIG_RCU_COMPAT_ARCH], [1])
+[
+fi
+]
+
+AC_ARG_ENABLE([smp-support], [ --disable-smp-support Disable SMP support. Warning: only use this
+ on uniprocessor systems. [[default=enabled]]], [def_smp_support=$enableval], [def_smp_support="yes"])
+
+[
+if test "$def_smp_support" = "no"; then
+ echo "SMP support disabled."
+else
+]
+ AC_DEFINE([CONFIG_RCU_SMP], [1])
+[
+ echo "SMP support enabled."
+fi
+]
+
+# From the sched_setaffinity(2)'s man page:
+# ~~~~
+# The CPU affinity system calls were introduced in Linux kernel 2.5.8.
+# The library interfaces were introduced in glibc 2.3. Initially, the
+# glibc interfaces included a cpusetsize argument. In glibc 2.3.3,
+# the cpuset size argument was removed, but this argument was
+# restored in glibc 2.3.4.
+# ~~~~
+
+# In addition to that, some vendors ported the system call to 2.4
+# kernels.
+
+# Furthermore, when the function first appeared, the MASK argument was
+# an unsigned long pointer, while later it was made into a cpu_set_t
+# pointer. Systems that have the cpu_set_t version also should have
+# the CPU_ZERO, CPU_SET, etc. macros.
+
+# All this mess means we have to cater for at least 3 different
+# sched_setaffinity prototypes:
+
+# ~~~~
+# int sched_setaffinity (pid_t pid, unsigned int len, unsigned long *mask);
+# int sched_setaffinity (pid_t __pid, size_t __cpusetsize, const cpu_set_t *__cpuset);
+# int sched_setaffinity (pid_t __pid, const cpu_set_t *__mask);
+# ~~~~
+
+dnl Since we define _GNU_SOURCE in the sources, must do so too in the
+dnl autoconf tests, as defining _GNU_SOURCE or not exposes
+dnl sched_setaffinity bits differently.
+saved_CFLAGS=$CFLAGS
+CFLAGS="$CFLAGS -D_GNU_SOURCE"
+
+# First check if the function is available at all.
+AC_CHECK_FUNCS(
+ [sched_setaffinity],
+ [ # Okay, we have it. Check if also have cpu_set_t. If we don't,
+ # then we have the first version using unsigned long, and no
+ # CPU_ZERO, etc. macros. If we do have cpu_set_t, we may have the
+ # version with 2 or 3 arguments. In that case, CPU_ZERO, etc.,
+ # should also be present, but we confirm nonetheless.
+
+ AC_CHECK_TYPES(
+ [cpu_set_t],
+ [ # We do have it. Confirm that we have CPU_ZERO, and it actually works.
+ AC_MSG_CHECKING([whether CPU_ZERO works])
+ AH_TEMPLATE([HAVE_CPU_ZERO],
+ [Define to 1 if we have CPU_ZERO and if it works])
+ AC_COMPILE_IFELSE(
+ [AC_LANG_PROGRAM(
+ [#define _GNU_SOURCE
+ #include <sched.h>],
+ [cpu_set_t foo; CPU_ZERO (&foo);])
+ ],
+ [ # Works!
+ AC_DEFINE(HAVE_CPU_ZERO, 1)
+ AC_MSG_RESULT([yes])
+ ],
+ [AC_MSG_RESULT([no])]
+ )