From d7907a557876fb0e28f1d708591ad9f2797362f6 Mon Sep 17 00:00:00 2001
From: Ivan Maidanski <ivmai@mail.ru>
Date: Tue, 6 Dec 2016 00:49:33 +0300
Subject: [PATCH] Fix potential data race in GC_SysVGetDataStart (SPARC)

* os_dep.c [SVR4 || AUX || DGUX || LINUX && SPARC]
(GC_SysVGetDataStart): Use AO_fetch_and_add(p,0) if available instead
of non-atomic read/write in *p = *p statement (thus, to avoid data race
though it is highly unlikely).
---
 os_dep.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/os_dep.c b/os_dep.c
index ae9c338..b78943a 100644
--- a/os_dep.c
+++ b/os_dep.c
@@ -1872,11 +1872,17 @@ void GC_register_data_segments(void)
     GC_setup_temporary_fault_handler();
     if (SETJMP(GC_jmp_buf) == 0) {
         /* Try writing to the address.  */
-        char v = *result;
-#       if defined(CPPCHECK)
-          GC_noop1((word)&v);
+#       ifdef AO_HAVE_fetch_and_add
+          volatile AO_t zero = 0;
+          (void)AO_fetch_and_add((volatile AO_t *)result, zero);
+#       else
+          /* Fallback to non-atomic fetch-and-store.    */
+          char v = *result;
+#         if defined(CPPCHECK)
+            GC_noop1((word)&v);
+#         endif
+          *result = v;
 #       endif
-        *result = v;
         GC_reset_fault_handler();
     } else {
         GC_reset_fault_handler();
-- 
2.7.4