randr: ProcRRGetProviders(): use stack for tiny temporary buffer

The reply payload buffer is very small and short-lived, so we can easily
use a local dynamic array for that, thus saving an extra heap alloc/free.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

randr/rrprovider.c

@@ -60,7 +60,6 @@ ProcRRGetProviders (ClientPtr client)
     ScreenPtr pScreen;
     rrScrPrivPtr pScrPriv;
     int rc;
-    CARD8 *extra;
     unsigned int extraLen;
     RRProvider *providers;
     int total_providers = 0, count_providers = 0;
@@ -96,6 +95,7 @@ ProcRRGetProviders (ClientPtr client)
     }
 
     extraLen = total_providers * sizeof(CARD32);
+    char extra[extraLen];
 
     xRRGetProvidersReply rep = {
         .type = X_Reply,
@@ -105,13 +105,6 @@ ProcRRGetProviders (ClientPtr client)
         .length = bytes_to_int32(extraLen),
     };
 
-    if (extraLen) {
-        extra = malloc(extraLen);
-        if (!extra)
-            return BadAlloc;
-    } else
-        extra = NULL;
-
     providers = (RRProvider *)extra;
     ADD_PROVIDER(pScreen);
     xorg_list_for_each_entry(iter, &pScreen->secondary_list, secondary_head) {
@@ -125,11 +118,7 @@ ProcRRGetProviders (ClientPtr client)
         swaps(&rep.nProviders);
     }
     WriteToClient(client, sizeof(xRRGetProvidersReply), (char *)&rep);
-    if (extraLen)
-    {
-        WriteToClient (client, extraLen, (char *) extra);
-        free(extra);
-    }
+    WriteToClient(client, extraLen, extra);
     return Success;
 }