From 4a0abd6869710393b39f2cadbbff0dc8c55b883b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20Guidi?= <cguidi@ciena.com>
Date: Fri, 10 Mar 2023 10:03:17 -0500
Subject: [PATCH] configure: Check for membarrier support
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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            |  1 +
 check-deps/Makefile.check      |  4 ++++
 check-deps/__have_membarrier.c | 10 ++++++++++
 configure                      |  3 +++
 4 files changed, 18 insertions(+)
 create mode 100644 check-deps/__have_membarrier.c

diff --git a/check-deps/Makefile b/check-deps/Makefile
index 2ca41b3ee..8f06dfae4 100644
--- a/check-deps/Makefile
+++ b/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
diff --git a/check-deps/Makefile.check b/check-deps/Makefile.check
index 93443e145..85042658d 100644
--- a/check-deps/Makefile.check
+++ b/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
diff --git a/check-deps/__have_membarrier.c b/check-deps/__have_membarrier.c
new file mode 100644
index 000000000..30a7c5a92
--- /dev/null
+++ b/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;
+}
diff --git a/configure b/configure
index 237e5619c..fe7289afd 100755
--- a/configure
+++ b/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