--core-file ; To get a core on SIGSEGV when using Linuxthreads

Docs/manual.texi:
  Documentation for --core-file
sql/mysql_priv.h:
  --core-file
sql/mysqld.cc:
  --core-file

Docs/manual.texi

@@ -5896,9 +5896,9 @@ of function} warnings. These may be ignored.
 @node Linux, Alpha-DEC-Unix, SunOS, Source install system issues
 @subsection Linux notes (all Linux versions)
 
-@strong{MySQL} uses LinuxThreads on Linux.  If you are using an old Linux
-version that doesn't have @code{glibc2}, you must install LinuxThreads before
-trying to compile
+@strong{MySQL} uses LinuxThreads on Linux.  If you are using an old
+Linux version that doesn't have @code{glibc2}, you must install
+LinuxThreads before trying to compile
 @strong{MySQL}. @uref{http://www.mysql.com/Downloads/Linux}
 
 Note that @code{glibc} versions before and including 2.1.1 has a fatal
@@ -5969,6 +5969,11 @@ If you see a dead @code{mysqld} daemon process with @code{ps}, this usually
 means that you have found a bug in @strong{MySQL} or you have got a corrupted
 table. @xref{Crashing}.
 
+If you want to get a core dump on Linux if mysqld dies with a SIGSEGV
+signal, you can start mysqld with the @code{--core-file} option.  Note
+that you also probably need to raise the @code{core file size} with
+@code{ulimit}!
+
 If you are using LinuxThreads and @code{mysqladmin shutdown} doesn't work,
 you must upgrade to LinuxThreads 0.7.1 or newer.
 
@@ -6165,6 +6170,10 @@ until you have installed @code{glibc} 2.0.7-19 from source!
 
 You can check which version of @code{glibc} you have with @code{rpm -q glibc}.
 
+Another reason for the above error is if you try to use more threads
+than your Linux kernel is configured for.  In this case you should rise
+the limits in @file{include/linux/tasks.h} and recompile your kernel!
+
 @node Linux-SPARC, Linux-Alpha, Linux-RedHat51, Linux
 @subsubsection Linux-SPARC notes
 
@@ -35686,6 +35695,9 @@ though, so 3.23 is not released as a stable version yet.
 @appendixsubsec Changes in release 3.23.23
 @itemize @bullet
 @item
+Added option @code{--core-file} to @code{mysqld} to get a core file on
+Linux if mysqld dies on the SIGSEGV signal
+@item
 @strong{MySQL} client 'mysql' now starts with option --no-named-commands
 (-g) by default. This option can be disabled with --enable-named-commands
 (-G). This may cause incompatibility problems in some cases, for example
@@ -40324,6 +40336,9 @@ old threads.  You can avoid this problem by starting @code{mysqld} with
 @code{-O thread_cache_size= 'max_connections +1'}.  In most cases just
 using @code{-O thread_cache_size= 5'} will help a lot!
 
+If you want to get a core dump on Linux if mysqld dies with a SIGSEGV signal,
+you can start mysqld with the @code{--core-file} option.
+
 If you are using gdb 4.17.x or above on Linux, you should install a
 @file{.gdb} file, with the following information, in your current
 directory:

sql/mysql_priv.h

@@ -127,7 +127,7 @@ void sql_element_free(void *ptr);
 #define TEST_NO_THREADS		32	/* For debugging under Linux */
 #define TEST_READCHECK		64	/* Force use of readcheck */
 #define TEST_NO_EXTRA		128
-#define TEST_KILL_ON_DEBUG	256	/* Kill server */
+#define TEST_CORE_ON_SIGNAL	256	/* Give core if signal */
 
 /* options for select set by the yacc parser */
 #define SELECT_DISTINCT		1

sql/mysqld.cc

@@ -1003,6 +1003,20 @@ static void init_signals(void)
 }
 #else
 
+#ifdef HAVE_LINUXTHREADS
+
+/* Produce a core for the thread */
+
+static sig_handler write_core(int sig)
+{
+  fprintf(stderr,"Got signal %s in thread %d\n",sys_siglist[sig],getpid());
+  signal(sig, SIG_DFL);
+  if (fork() != 0) exit(1);			// Abort main program
+  // Core will be written at exit
+}
+#endif
+
+
 static void init_signals(void)
 {
   sigset_t set;
@@ -1012,6 +1026,16 @@ static void init_signals(void)
 
   sigset(THR_KILL_SIGNAL,end_thread_signal);
   sigset(THR_SERVER_ALARM,print_signal_warning); // Should never be called!
+#ifdef HAVE_LINUXTHREADS
+  if (test_flags & TEST_CORE_ON_SIGNAL)
+  {
+    struct sigaction sa; sa.sa_flags = 0;
+    sigemptyset(&sa.sa_mask);
+    sigprocmask(SIG_SETMASK,&sa.sa_mask,NULL);
+    sa.sa_handler=write_core;
+    sigaction(SIGSEGV, &sa, NULL);
+  }
+#endif
   (void) sigemptyset(&set);
 #ifdef THREAD_SPECIFIC_SIGPIPE
   sigset(SIGPIPE,abort_thread);
@@ -2134,7 +2158,7 @@ enum options {OPT_ISAM_LOG=256,OPT_SKIP_NEW,OPT_SKIP_GRANT,
 	      OPT_MASTER_PORT, OPT_MASTER_INFO_FILE, OPT_MASTER_CONNECT_RETRY,
               OPT_SQL_BIN_UPDATE_SAME, OPT_REPLICATE_DO_DB,
 	      OPT_REPLICATE_IGNORE_DB, OPT_LOG_SLAVE_UPDATES,
-              OPT_BINLOG_DO_DB, OPT_BINLOG_IGNORE_DB};
+              OPT_BINLOG_DO_DB, OPT_BINLOG_IGNORE_DB, OPT_WANT_CORE};
 
 static struct option long_options[] =
 {
@@ -2156,6 +2180,7 @@ static struct option long_options[] =
 #ifdef __WIN__
   {"console",		no_argument,	  0,  OPT_CONSOLE},
 #endif
+  {"core-file",		no_argument,	   0, OPT_WANT_CORE},
   {"chroot",		required_argument,0,  'r'},
   {"character-sets-dir",required_argument,0,  OPT_CHARSETS_DIR},
   {"datadir",		required_argument, 0, 'h'},
@@ -2188,8 +2213,10 @@ static struct option long_options[] =
   {"master-connect-retry", required_argument, 0, (int) OPT_MASTER_CONNECT_RETRY},
   {"master-info-file",  required_argument, 0, (int) OPT_MASTER_INFO_FILE},
   {"new",		no_argument,	   0, 'n'},
-  {"old-protocol",	no_argument,	0, 'o'},
+  {"old-protocol",	no_argument,	   0, 'o'},
+#ifndef DBUG_OFF
   {"one-thread",	no_argument,	   0, OPT_ONE_THREAD},
+#endif
   {"pid-file",		required_argument, 0, (int) OPT_PID_FILE},
   {"port",		required_argument, 0, 'P'},
   {"replicate-do-db", required_argument, 0, OPT_REPLICATE_DO_DB},
@@ -2432,6 +2459,7 @@ static void usage(void)
   --character-sets-dir=...\n\
                         Directory where character sets are\n\
   --chroot=path		Chroot mysqld daemon during startup\n\
+  --core-file		Write core on errors\n\
   -h, --datadir=path	Path to the database root");
 #ifndef DBUG_OFF
   printf("\
@@ -2465,9 +2493,11 @@ static void usage(void)
   --pid-file=path	Pid file used by safe_mysqld\n\
   -P, --port=...	Port number to use for connection\n\
   -n, --new		Use very new possible 'unsafe' functions\n\
-  -o, --old-protocol	Use the old (3.20) protocol\n\
+  -o, --old-protocol	Use the old (3.20) protocol\n");
+#ifndef DBUG_OFF
+  puts("\
   --one-thread		Only use one thread (for debugging under Linux)\n");
-  /* We have to break the string here because of VC++ limits */
+#endif
   puts("\
   -O, --set-variable var=option\n\
 			Give a variable an value. --help lists variables\n\
@@ -2729,8 +2759,6 @@ static void get_options(int argc,char **argv)
 	binlog_do_db.push_back(db);
         break;
       }
-
-
     case (int) OPT_SQL_BIN_UPDATE_SAME:
       opt_sql_bin_update  = 1;
       break;
@@ -2785,6 +2813,9 @@ static void get_options(int argc,char **argv)
     case (int) OPT_ONE_THREAD:
       test_flags |= TEST_NO_THREADS;
       break;
+    case (int) OPT_WANT_CORE:
+      test_flags |= TEST_CORE_ON_SIGNAL;
+      break;
     case (int) OPT_BIND_ADDRESS:
       if (optarg && isdigit(optarg[0]))
       {