[lttng-dev] [PATCH] Force static_alloc setup to be written into memory

[paul_woegerer@mentor.com (Paul Woegerer)]

As explained by Alexander Monakov, dlsym() is defined to be pure, thus the
compiler is allowed to assume that there is no need to write the changes
performed by setup_static_allocator() into memory prior to calling dlsym().
The added cmm_barrier() forces the compiler to write the changes into memory.

For more details refer to:
http://lists.lttng.org/pipermail/lttng-dev/2014-February/022389.html

Signed-off-by: Paul Woegerer <paul_woegerer at mentor.com>
---
 liblttng-ust-libc-wrapper/lttng-ust-malloc.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/liblttng-ust-libc-wrapper/lttng-ust-malloc.c b/liblttng-ust-libc-wrapper/lttng-ust-malloc.c
index 8296ae2..7dd647f 100644
--- a/liblttng-ust-libc-wrapper/lttng-ust-malloc.c
+++ b/liblttng-ust-libc-wrapper/lttng-ust-malloc.c
@@ -198,6 +198,9 @@ void lookup_all_symbols(void)
 	 */
 	setup_static_allocator();
 
+	/* Dlsym is defined pure -> force static alloc into memory */
+	cmm_barrier();
+
 	/* Perform the actual lookups */
 	af.calloc = dlsym(RTLD_NEXT, "calloc");
 	af.malloc = dlsym(RTLD_NEXT, "malloc");
@@ -207,7 +210,7 @@ void lookup_all_symbols(void)
 	af.posix_memalign = dlsym(RTLD_NEXT, "posix_memalign");
 
 	/* Populate the new allocator functions */
-	memcpy(&cur_alloc, &af, sizeof(cur_alloc));
+	cur_alloc = af;
 }
 
 void *malloc(size_t size)
-- 
1.8.5.2