[Mesa-dev] [PATCH] util/ralloc: Remove double zero'ing of rzalloc buffers

[Jordan Justen]

Juha-Pekka found this back in May 2015:
<1430915727-28677-1-git-send-email-juhapekka.heikkila at gmail.com>

>From the discussion, obviously it would be preferable to make
ralloc_size no longer return zeroed memory, but Juha-Pekka found that
it would break Mesa.

For now, let's point out the flaw, and stop doing the double zeroing
of rzalloc buffers.

Signed-off-by: Jordan Justen <jordan.l.justen at intel.com>
Cc: Juha-Pekka Heikkila <juhapekka.heikkila at gmail.com>
Cc: Kenneth Graunke <kenneth at whitecape.org>
---

 For a release build, I saw the code size shrink by 64 bytes.

 src/util/ralloc.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/util/ralloc.c b/src/util/ralloc.c
index 6d4032b..24c1eee 100644
--- a/src/util/ralloc.c
+++ b/src/util/ralloc.c
@@ -49,6 +49,14 @@ _CRTIMP int _vscprintf(const char *format, va_list argptr);
 #endif
 #endif
 
+/* ralloc_size has always used calloc to allocate memory. This has allowed
+ * code using ralloc_size to depend on always receiving a cleared buffer.
+ *
+ * FIXME: Clean up the code base to allow this to be set to false, and then
+ * remove it altogether.
+ */
+static const bool always_allocate_zeroed_memory = true;
+
 #define CANARY 0x5A1106
 
 struct ralloc_header
@@ -110,7 +118,10 @@ ralloc_context(const void *ctx)
 void *
 ralloc_size(const void *ctx, size_t size)
 {
-   void *block = calloc(1, size + sizeof(ralloc_header));
+   void *block =
+      always_allocate_zeroed_memory ?
+      calloc(1, size + sizeof(ralloc_header)) :
+      malloc(size + sizeof(ralloc_header));
    ralloc_header *info;
    ralloc_header *parent;
 
@@ -132,7 +143,7 @@ void *
 rzalloc_size(const void *ctx, size_t size)
 {
    void *ptr = ralloc_size(ctx, size);
-   if (likely(ptr != NULL))
+   if (!always_allocate_zeroed_memory && likely(ptr != NULL))
       memset(ptr, 0, size);
    return ptr;
 }
-- 
2.6.2