From eaa94147a822f9c56d5842d6ff601aa39cf05a63 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jean-S=C3=A9bastien=20P=C3=A9dron?=
 <jean-sebastien.pedron@dumbbell.fr>
Date: Wed, 2 Sep 2015 15:21:41 +0200
Subject: [PATCH] ralloc: Use __attribute__((destructor)) instead of atexit(3)

... to free the ralloc context at program exit.

On Linux, atexit(3) handlers are called when the program exits but also
when a library is unloaded. The latter behavior is a Glibc extension.

On systems where this extension is not supported, this causes an
application to crash when, for instance, a library using ralloc is
dlclosed: at program exit, the registered function is no longer in
memory. For example, this happens with OpenCL applications using an ICD
loader on FreeBSD.

__attribute__((destructor)) fixes the problem because such handlers are
called when a library is unloaded and when the program exits.
---
 configure.ac      | 1 +
 src/util/macros.h | 6 ++++++
 src/util/ralloc.c | 5 +++--
 src/util/ralloc.h | 9 ++++++---
 4 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/configure.ac b/configure.ac
index 90ba4fe..f4ab843 100644
--- a/configure.ac
+++ b/configure.ac
@@ -209,6 +209,7 @@ AX_GCC_BUILTIN([__builtin_popcountll])
 AX_GCC_BUILTIN([__builtin_unreachable])
 
 AX_GCC_FUNC_ATTRIBUTE([const])
+AX_GCC_FUNC_ATTRIBUTE([destructor])
 AX_GCC_FUNC_ATTRIBUTE([flatten])
 AX_GCC_FUNC_ATTRIBUTE([format])
 AX_GCC_FUNC_ATTRIBUTE([malloc])
diff --git a/src/util/macros.h b/src/util/macros.h
index 84e4f18..539aba4 100644
--- a/src/util/macros.h
+++ b/src/util/macros.h
@@ -114,6 +114,12 @@ do {                       \
 #define ATTRIBUTE_CONST
 #endif
 
+#ifdef HAVE_FUNC_ATTRIBUTE_DESTRUCTOR
+#define DESTRUCTOR __attribute__((destructor))
+#else
+#define DESTRUCTOR
+#endif
+
 #ifdef HAVE_FUNC_ATTRIBUTE_FLATTEN
 #define FLATTEN __attribute__((__flatten__))
 #else
diff --git a/src/util/ralloc.c b/src/util/ralloc.c
index 01719c8..09b9524 100644
--- a/src/util/ralloc.c
+++ b/src/util/ralloc.c
@@ -311,7 +311,7 @@ ralloc_parent(const void *ptr)
 
 static void *autofree_context = NULL;
 
-static void
+static DESTRUCTOR void
 autofree(void)
 {
    ralloc_free(autofree_context);
@@ -322,7 +322,8 @@ ralloc_autofree_context(void)
 {
    if (unlikely(autofree_context == NULL)) {
       autofree_context = ralloc_context(NULL);
-      atexit(autofree);
+      /* autofree_context is freed at program exit or library unload in
+       * autofree() above. */
    }
    return autofree_context;
 }
diff --git a/src/util/ralloc.h b/src/util/ralloc.h
index 7587e11..d8c6cc0 100644
--- a/src/util/ralloc.h
+++ b/src/util/ralloc.h
@@ -249,9 +249,12 @@ void *ralloc_parent(const void *ptr);
 /**
  * Return a context whose memory will be automatically freed at program exit.
  *
- * The first call to this function creates a context and registers a handler
- * to free it using \c atexit.  This may cause trouble if used in a library
- * loaded with \c dlopen.
+ * The first call to this function creates a context.
+ *
+ * The context is freed in a function registered with
+ * \c __attribute__((destructor)). \c atexit is not used for this
+ * purpose as it would crash when used in a library loaded with
+ * \c dlopen.
  */
 void *ralloc_autofree_context(void);
 
-- 
2.4.6