configure: Check for membarrier support

Runtime dynamic patching requires cache synchronization. This is best
achieved by using the 'MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE'
memory barrier. However it was introduced in Linux 4.16. We set a flag
indicating whether this membarrier can be used or if libmcount has to
rely on other mechanisms (e.g. signals).

Signed-off-by: Clément Guidi <cguidi@ciena.com>

check-deps/Makefile

@@ -14,6 +14,7 @@ CHECK_LIST += have_libdw
 CHECK_LIST += have_libunwind
 CHECK_LIST += have_libcapstone
 CHECK_LIST += cc_has_minline_all_stringops
+CHECK_LIST += have_membarrier
 
 #
 # This is needed for checking build dependency

check-deps/Makefile.check

@@ -82,3 +82,7 @@ endif
 ifneq ($(wildcard $(objdir)/check-deps/cc_has_minline_all_stringops),)
   LIB_CFLAGS += -minline-all-stringops
 endif
+
+ifneq ($(wildcard $(objdir)/check-deps/have_membarrier),)
+  LIB_CFLAGS += -DHAVE_MEMBARRIER
+endif

check-deps/__have_membarrier.c

@@ -0,0 +1,10 @@
+#include <linux/membarrier.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+int main()
+{
+	syscall(__NR_membarrier, MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE, 0, 0);
+	syscall(__NR_membarrier, MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE, 0, 0);
+	return 0;
+}

configure

@@ -35,6 +35,7 @@ usage() {
   --without-capstone    build without libcapstone            (even if found on the system)
   --without-perf        build without perf event             (even if available)
   --without-schedule    build without scheduler event        (even if available)
+  --without-membarrier  build without membarriers            (even if available)
 
   --arch=<ARCH>         set target architecture              (default: system default arch)
                         e.g. x86_64, aarch64, i386, or arm
@@ -198,6 +199,7 @@ for dep in $IGNORE; do
         capstone)    TARGET=have_libcapstone   ;;
         perf*)       TARGET=perf_clockid       ;;
         sched*)      TARGET=perf_context_switch;;
+        membarrier)  TARGET=have_membarrier    ;;
         *)           ;;
     esac
     if [ ! -z "$TARGET" ]; then
@@ -265,6 +267,7 @@ print_feature "perf_event" "perf_clockid" "perf (PMU) event support"
 print_feature "schedule" "perf_context_switch" "scheduler event support"
 print_feature "capstone" "have_libcapstone" "full dynamic tracing support"
 print_feature "libunwind" "have_libunwind" "stacktrace support (optional for debugging)"
+print_feature "membarrier" "have_membarrier" "membarrier support (requires Linux 4.16)"
 
 cat >$output <<EOF
 # this file is generated automatically