From: jb <jb@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Sun, 2 Dec 2018 15:12:44 +0000 (+0000)
Subject: Use atomic load/store to access static backtrace state pointer
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cfc2cc93c38f91f0f52d428141d5bb0bcfd922d7;p=thirdparty%2Fgcc.git

Use atomic load/store to access static backtrace state pointer

As the static backtrace state pointer can be accessed from multiple
threads, use atomics to access it.

Regtested on x86_64-pc-linux-gnu.

libgfortran/ChangeLog:

2018-12-02  Janne Blomqvist  <jb@gcc.gnu.org>

	PR libfortran/88137
	* runtime/backtrace.c (show_backtrace): Use atomic load/store to
	access the static lbstate pointer.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@266724 138bc75d-0d04-0410-961f-82ee72b054a4
---

diff --git a/libgfortran/ChangeLog b/libgfortran/ChangeLog
index f1f7cbe4effe..42dbc8034430 100644
--- a/libgfortran/ChangeLog
+++ b/libgfortran/ChangeLog
@@ -1,3 +1,9 @@
+2018-12-02  Janne Blomqvist  <jb@gcc.gnu.org>
+
+	PR libfortran/88137
+	* runtime/backtrace.c (show_backtrace): Use atomic load/store to
+	access the static lbstate pointer.
+
 2018-11-30  Janne Blomqvist  <jb@gcc.gnu.org>
 
 	PR libfortran/88137
diff --git a/libgfortran/runtime/backtrace.c b/libgfortran/runtime/backtrace.c
index 3fc973a5e6da..93ea14af19d9 100644
--- a/libgfortran/runtime/backtrace.c
+++ b/libgfortran/runtime/backtrace.c
@@ -149,15 +149,20 @@ show_backtrace (bool in_signal_handler)
   /* Note that libbacktrace allows the state to be accessed from
      multiple threads, so we don't need to use a TLS variable for the
      state here.  */
-  static struct backtrace_state *lbstate;
+  static struct backtrace_state *lbstate_saved;
+  struct backtrace_state *lbstate;
   struct mystate state = { 0, false, in_signal_handler };
 
+  lbstate = __atomic_load_n (&lbstate_saved, __ATOMIC_RELAXED);
   if (!lbstate)
-    lbstate = backtrace_create_state (NULL, __gthread_active_p (),
-				      error_callback, NULL);
-
-  if (lbstate == NULL)
-    return;
+    {
+      lbstate = backtrace_create_state (NULL, __gthread_active_p (),
+					error_callback, NULL);
+      if (lbstate)
+	__atomic_store_n (&lbstate_saved, lbstate, __ATOMIC_RELAXED);
+      else
+	return;
+    }
 
   if (!BACKTRACE_SUPPORTED || (in_signal_handler && BACKTRACE_USES_MALLOC))
     {