MDEV-14315 -- Reflect use of tcmalloc in a system variable and error log

* The version of tcmalloc is written to the system variable
    'version_malloc_library' if tcmalloc is used, similarly to
    jemalloc
  * Extracted method guess_malloc_library()

include/my_sys.h

@@ -154,6 +154,8 @@ typedef struct my_aio_result {
 /* Extra length needed for filename if one calls my_create_backup_name */
 #define MY_BACKUP_NAME_EXTRA_LENGTH 17
 
+char *guess_malloc_library();
+
 /* If we have our own safemalloc (for debugging) */
 #if defined(SAFEMALLOC)
 void sf_report_leaked_memory(my_thread_id id);

mysys/CMakeLists.txt

@@ -37,6 +37,7 @@ SET(MYSYS_SOURCES  array.c charset-def.c charset.c checksum.c my_default.c
 				thr_rwlock.c thr_timer.c
                                 tree.c typelib.c base64.c my_memmem.c
                                 my_getpagesize.c
+                                guess_malloc_library.c
 				lf_alloc-pin.c lf_dynarray.c lf_hash.c
                                 safemalloc.c my_new.cc
 				my_atomic.c my_getncpus.c my_safehash.c my_chmod.c my_rnd.c

mysys/guess_malloc_library.c

@@ -0,0 +1,63 @@
+/* Copyright (c) 2002, 2015, Oracle and/or its affiliates.
+   Copyright (c) 2012, 2017, MariaDB Corporation.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; version 2 of the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
+
+/* guess_malloc_library() deduces, to the best of its ability,
+   the currently used malloc library and its version */
+
+#include <stddef.h>
+#include <m_string.h>
+
+char *guess_malloc_library()
+{
+#ifndef HAVE_DLOPEN
+  return (char*) MALLOC_LIBRARY;
+#else
+  static char buf[128];
+
+  if (strcmp(MALLOC_LIBRARY, "system") != 0)
+  {
+    return (char*) MALLOC_LIBRARY;
+  }
+
+  /* tcmalloc */
+  typedef const char* (*tc_version_type)(int*, int*, const char**);
+  tc_version_type tc_version_func =
+    (tc_version_type) dlsym(RTLD_DEFAULT, "tc_version");
+  if (tc_version_func)
+  {
+    int major, minor;
+    const char* ver_str = tc_version_func(&major, &minor, NULL);
+    strxnmov(buf, sizeof(buf)-1, "tcmalloc ", ver_str, NULL);
+    return buf;
+  }
+
+  /* jemalloc */
+  typedef int (*mallctl_type)(const char*, void*, size_t*, void*, size_t);
+  mallctl_type mallctl_func =
+    (mallctl_type) dlsym(RTLD_DEFAULT, "mallctl");
+  if (mallctl_func)
+  {
+    char *ver;
+    size_t len = sizeof(ver);
+    mallctl_func("version", &ver, &len, NULL, 0);
+    strxnmov(buf, sizeof(buf)-1, "jemalloc ", ver, NULL);
+    return buf;
+  }
+
+  return (char*) MALLOC_LIBRARY;
+#endif
+}
+

sql/sys_vars.cc

@@ -35,6 +35,7 @@
 #include "sql_priv.h"
 #include "sql_class.h"                          // set_var.h: THD
 #include "sys_vars.ic"
+#include "my_sys.h"
 
 #include "events.h"
 #include <thr_alarm.h>
@@ -3511,27 +3512,6 @@ static Sys_var_charptr Sys_version_source_revision(
        CMD_LINE_HELP_ONLY,
        IN_SYSTEM_CHARSET, DEFAULT(SOURCE_REVISION));
 
-static char *guess_malloc_library()
-{
-  if (strcmp(MALLOC_LIBRARY, "system") == 0)
-  {
-#ifdef HAVE_DLOPEN
-    typedef int (*mallctl_type)(const char*, void*, size_t*, void*, size_t);
-    mallctl_type mallctl_func;
-    mallctl_func= (mallctl_type)dlsym(RTLD_DEFAULT, "mallctl");
-    if (mallctl_func)
-    {
-      static char buf[128];
-      char *ver;
-      size_t len = sizeof(ver);
-      mallctl_func("version", &ver, &len, NULL, 0);
-      strxnmov(buf, sizeof(buf)-1, "jemalloc ", ver, NULL);
-      return buf;
-    }
-#endif
-  }
-  return const_cast<char*>(MALLOC_LIBRARY);
-}
 static char *malloc_library;
 static Sys_var_charptr Sys_malloc_library(
        "version_malloc_library", "Version of the used malloc library",