adding freezero and quick tests

Author: devnexen

src/override/malloc.cc

@@ -71,6 +71,22 @@ extern "C"
     }
     return ThreadAlloc::get().alloc<ZeroMem::YesZero, CoreDumpMem::NoDump>(sz);
   }
+
+  SNMALLOC_EXPORT void SNMALLOC_NAME_MANGLE(freezero)(void* p, size_t size)
+  {
+    if (SNMALLOC_UNLIKELY(p == nullptr))
+    {
+      return;
+    }
+
+    size_t sz = bits::min(size, ThreadAlloc::get().alloc_size(p));
+    /* we are not trying to be fast, here but disallowing to potentially
+     * optimize away the memset call */
+    void* (*volatile memset_fn)(void*, int, size_t) = memset;
+    memset_fn(p, 0, sz);
+
+    ThreadAlloc::get().dealloc(p);
+  }
 #endif
 
   SNMALLOC_EXPORT

src/test/func/malloc/malloc.cc

@@ -229,6 +229,17 @@ int main(int argc, char** argv)
     check_result(size + 1, 1, our_malloc_conceal(size + 1), SUCCESS, false);
   }
 
+  our_freezero(nullptr, 1024);
+  void* p = our_malloc_conceal(64);
+  our_freezero(p, 128);
+  if (((uint8_t*)p)[63] != 0)
+  {
+    abort();
+  }
+
+  p = our_malloc_conceal(16);
+  our_freezero(p, 0);
+
   for (smallsizeclass_t sc = 0; sc < NUM_SMALL_SIZECLASSES; sc++)
   {
     const size_t size = sizeclass_to_size(sc);