MDEV-36542 Remove UNINIT_VAR(x)=x under UBSAN

Clang processes the "int x=x" code from UNINIT_VAR
literally resulting in an uninitialized read and write.
This is something we want to avoid. Gcc does the same
without emitting warnings.

As the UNINIT_VAR was around avoiding compiler false detection,
and clang doesn't false detect, is default action is a
noop.

Static analysers (examined Infer and SonarQube) are
clang based and have the same detection.

Using a __clang__ instead of WITH_UBSAN would acheived
a better result, however reviewer wanted to keep WITH_UBSAN
only.

LINT_INIT_STRUCT is no longer required, even a gcc-4.8.5
doesn't warn with this construct removed which matches
the comment that it was fixed in gcc ~4.7.

mysql.cc - all paths in com_go populate buff before use.

json: Item_func_json_merge::val_str
  LINT_INIT(js2) unneeded as usage in the previous statements
  it is explicitly initialized to NULL.

Item_func_json_contains_path::val_bool n_found is guarded
by an uninitialized read by mode_one and from
gcc-13.3.0 in Ubuntu 24.04 this is detected. As the only
remaining use of LINIT_INIT this usage has been applied
with the expanded macro with the unused _lint define removed.

The LINT_INIT macro is removed.

_ma_ck_delete - org_key only valid under share->now_transactional
likewise with _ma_ck_write_btree_with_log

connect engine never used anything that FORCE_INIT_OF_VARS
would change.

Reviewer: Monty

Author: grooverdan

client/mysql.cc

@@ -3499,8 +3499,6 @@ static int com_go(String *buffer, char *)
     old_buffer.copy();
   }
 
-  /* Remove garbage for nicer messages */
-  LINT_INIT_STRUCT(buff[0]);
   remove_cntrl(*buffer);
 
   if (buffer->is_empty())

include/m_string.h

@@ -79,12 +79,6 @@ extern const char _dig_vec_lower[];
 
 extern char *strmov_overlapp(char *dest, const char *src);
 
-#if defined(_lint) || defined(FORCE_INIT_OF_VARS)
-#define LINT_INIT_STRUCT(var) bzero(&var, sizeof(var)) /* No uninitialize-warning */
-#else
-#define LINT_INIT_STRUCT(var)
-#endif
-
 /* Prototypes for string functions */
 
 extern	void bmove_upp(uchar *dst,const uchar *src,size_t len);

include/my_global.h

@@ -448,22 +448,19 @@ extern "C" int madvise(void *addr, size_t len, int behav);
 /*
    Suppress uninitialized variable warning without generating code.
 */
-#if defined(__GNUC__)
-/* GCC specific self-initialization which inhibits the warning. */
+#if defined(__GNUC__) && !defined(WITH_UBSAN)
+/*
+  GCC specific self-initialization which inhibits the warning.
+  clang and static analysis will complain loudly about this
+  so compile those under WITH_UBSAN.
+*/
 #define UNINIT_VAR(x) x= x
-#elif defined(_lint) || defined(FORCE_INIT_OF_VARS)
+#elif defined(FORCE_INIT_OF_VARS)
 #define UNINIT_VAR(x) x= 0
 #else
 #define UNINIT_VAR(x) x
 #endif
 
-/* This is only to be used when resetting variables in a class constructor */
-#if defined(_lint) || defined(FORCE_INIT_OF_VARS)
-#define LINT_INIT(x) x= 0
-#else
-#define LINT_INIT(x)
-#endif
-
 #if !defined(HAVE_UINT)
 #undef HAVE_UINT
 #define HAVE_UINT

sql/item_jsonfunc.cc

@@ -1728,9 +1728,16 @@ bool Item_func_json_contains_path::val_bool()
   longlong result;
   json_path_t p;
   int n_found;
-  LINT_INIT(n_found);
   int array_sizes[JSON_DEPTH_LIMIT];
   uint has_negative_path= 0;
+#if defined(FORCE_INIT_OF_VARS)
+  /*
+    Initialization force not required after gcc 13.3
+    where it correctly sees that an uninitialized read
+    of n_found doesn't occur with mode_one being true.
+  */
+  n_found= 0; 
+#endif
 
   if ((null_value= args[0]->null_value))
     return 0;
@@ -1770,8 +1777,6 @@ bool Item_func_json_contains_path::val_bool()
     bzero(p_found, (arg_count-2) * sizeof(bool));
     n_found= arg_count - 2;
   }
-  else
-    n_found= 0; /* Just to prevent 'uninitialized value' warnings */
 
   result= 0;
   while (json_get_path_next(&je, &p) == 0)
@@ -2644,7 +2649,6 @@ String *Item_func_json_merge::val_str(String *str)
   String *js1= args[0]->val_json(&tmp_js1), *js2=NULL;
   uint n_arg;
   THD *thd= current_thd;
-  LINT_INIT(js2);
 
   JSON_DO_PAUSE_EXECUTION(thd, 0.0002);
 

storage/connect/CMakeLists.txt

@@ -46,7 +46,7 @@ user_connect.h valblk.h value.h xindex.h xobject.h xtable.h)
 #
 # Definitions that are shared for all OSes
 #
-add_definitions( -DMARIADB -DFORCE_INIT_OF_VARS -Dconnect_EXPORTS)
+add_definitions( -DMARIADB -Dconnect_EXPORTS)
 add_definitions( -DHUGE_SUPPORT -DGZ_SUPPORT )
 
 macro(DISABLE_WARNING W)

storage/maria/ma_delete.c

@@ -165,8 +165,6 @@ my_bool _ma_ck_delete(MARIA_HA *info, MARIA_KEY *key)
   MARIA_KEY org_key;
   DBUG_ENTER("_ma_ck_delete");
 
-  LINT_INIT_STRUCT(org_key);
-
   alloc_on_stack(*info->stack_end_ptr, key_buff, buff_alloced,
                  key->keyinfo->max_store_length);
   if (!key_buff)

storage/maria/ma_write.c

@@ -483,8 +483,6 @@ static my_bool _ma_ck_write_btree_with_log(MARIA_HA *info, MARIA_KEY *key,
   my_bool transactional= share->now_transactional;
   DBUG_ENTER("_ma_ck_write_btree_with_log");
 
-  LINT_INIT_STRUCT(org_key);
-
   if (transactional)
   {
     /* Save original value as the key may change */