+AH_TEMPLATE([CONFIG_RCU_TLS], [TLS provided by the compiler.])
+AH_TEMPLATE([CONFIG_RCU_HAVE_CLOCK_GETTIME], [clock_gettime() is detected.])
+AH_TEMPLATE([CONFIG_RCU_FORCE_SYS_MEMBARRIER], [Require the operating system to support the membarrier system call for default and bulletproof flavors.])
+
+# Allow requiring the operating system to support the membarrier system
+# call. Applies to default and bulletproof flavors.
+AC_ARG_ENABLE([sys-membarrier-fallback],
+ AS_HELP_STRING([--disable-sys-membarrier-fallback], [Abort if sys-membarrier is needed but not available rather than using a fallback.]),
+ [def_sys_membarrier_fallback=$enableval],
+ [def_sys_membarrier_fallback="yes"])
+AS_IF([test "x$def_sys_membarrier_fallback" != "xyes"], [AC_DEFINE([CONFIG_RCU_FORCE_SYS_MEMBARRIER], [1])])
+
+# Allow overriding storage used for TLS variables.
+AC_ARG_ENABLE([compiler-tls],
+ AS_HELP_STRING([--disable-compiler-tls], [Use pthread_getspecific() to emulate Thread Local Storage (TLS) variables.]),
+ [def_compiler_tls=$enableval],
+ [def_compiler_tls="yes"])
+
+# If not overridden, use ax_tls.m4 to check if TLS is available.
+AS_IF([test "x$def_compiler_tls" = "xyes"],
+ [AX_TLS([def_tls_detect=$ac_cv_tls], [:])],
+ [:])
+
+AS_IF([test "x$def_tls_detect" = "x"],
+ [:],
+ [AC_DEFINE_UNQUOTED([CONFIG_RCU_TLS], $def_tls_detect)])
+
+# Checks for C compiler
+AC_USE_SYSTEM_EXTENSIONS
+AC_PROG_CC
+AC_PROG_CC_STDC