[PATCH 3/3 v4] Demangler crash handler

[Gary Benson <gbenson at redhat dot com>]

This patch wraps calls to the demangler with a segmentation fault
handler.  The first time a segmentation fault is caught a core file
is generated and the user is prompted to file a bug and offered the
choice to exit or to continue their GDB session.  A maintainence
option is provided to allow the user to disable the crash handler
if required.


gdb/
2014-06-05  Gary Benson  <gbenson@redhat.com>

	* configure.ac [AC_CHECK_FUNCS] <sigaltstack>: New check.
	* configure: Regenerate.
	* config.in: Likewise.
	* main.c (signal.h): New include.
	(setup_alternate_signal_stack): New function.
	(captured_main): Call the above.
	* cp-support.c (signal.h): New include.
	(catch_demangler_crashes): New flag.
	(SIGJMP_BUF): New define.
	(SIGSETJMP): Likewise.
	(SIGLONGJMP): Likewise.
	(gdb_demangle_jmp_buf): New static global.
	(gdb_demangle_attempt_core_dump): Likewise.
	(gdb_demangle_signal_handler): New function.
	(gdb_demangle): If catch_demangler_crashes is set, install the
	above signal handler before calling bfd_demangle, and restore
	the original signal handler afterwards.  Display the offending
	symbol and call demangler_warning the first time a segmentation
	fault is caught.
	(_initialize_cp_support): New maint set/show command.

gdb/doc/
2014-06-05  Gary Benson  <gbenson@redhat.com>

	* gdb.texinfo (Maintenance Commands): Document new
	"maint set/show catch-demangler-crashes" option.

diff --git a/gdb/configure.ac b/gdb/configure.ac
index 903f378..f41ba2f 100644
--- a/gdb/configure.ac
+++ b/gdb/configure.ac
@@ -1328,7 +1328,7 @@ AC_CHECK_FUNCS([canonicalize_file_name realpath getrusage getuid getgid \
 		sigaction sigprocmask sigsetmask socketpair \
 		ttrace wborder wresize setlocale iconvlist libiconvlist btowc \
 		setrlimit getrlimit posix_madvise waitpid lstat \
-		ptrace64])
+		ptrace64 sigaltstack])
 AM_LANGINFO_CODESET
 GDB_AC_COMMON
 
diff --git a/gdb/configure b/gdb/configure
index 56c92d3..e23a58f 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -10507,7 +10507,7 @@ for ac_func in canonicalize_file_name realpath getrusage getuid getgid \
 		sigaction sigprocmask sigsetmask socketpair \
 		ttrace wborder wresize setlocale iconvlist libiconvlist btowc \
 		setrlimit getrlimit posix_madvise waitpid lstat \
-		ptrace64
+		ptrace64 sigaltstack
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
diff --git a/gdb/config.in b/gdb/config.in
index cd4ce92..8585b49 100644
--- a/gdb/config.in
+++ b/gdb/config.in
@@ -366,6 +366,9 @@
 /* Define to 1 if you have the `sigaction' function. */
 #undef HAVE_SIGACTION
 
+/* Define to 1 if you have the `sigaltstack' function. */
+#undef HAVE_SIGALTSTACK
+
 /* Define to 1 if you have the <signal.h> header file. */
 #undef HAVE_SIGNAL_H
 
diff --git a/gdb/main.c b/gdb/main.c
index a9fc378..7031cc3 100644
--- a/gdb/main.c
+++ b/gdb/main.c
@@ -45,6 +45,7 @@
 
 #include "filenames.h"
 #include "filestuff.h"
+#include <signal.h>
 
 /* The selected interpreter.  This will be used as a set command
    variable, so it should always be malloc'ed - since
@@ -288,6 +289,27 @@ get_init_files (const char **system_gdbinit,
   *local_gdbinit = localinit;
 }
 
+/* Try to set up an alternate signal stack for SIGSEGV handlers.
+   This allows us to handle SIGSEGV signals generated when the
+   normal process stack is exhausted.  If this stack is not set
+   up (sigaltstack is unavailable or fails) and a SIGSEGV is
+   generated when the normal stack is exhausted then the program
+   will behave as though no SIGSEGV handler was installed.  */
+
+static void
+setup_alternate_signal_stack (void)
+{
+#ifdef HAVE_SIGALTSTACK
+  stack_t ss;
+
+  ss.ss_sp = xmalloc (SIGSTKSZ);
+  ss.ss_size = SIGSTKSZ;
+  ss.ss_flags = 0;
+
+  sigaltstack(&ss, NULL);
+#endif
+}
+
 /* Call command_loop.  If it happens to return, pass that through as a
    non-zero return status.  */
 
@@ -785,6 +807,9 @@ captured_main (void *data)
       quiet = 1;
   }
 
+  /* Try to set up an alternate signal stack for SIGSEGV handlers.  */
+  setup_alternate_signal_stack ();
+
   /* Initialize all files.  Give the interpreter a chance to take
      control of the console via the deprecated_init_ui_hook ().  */
   gdb_init (gdb_program_name);
diff --git a/gdb/cp-support.c b/gdb/cp-support.c
index 91533e8..f4dde70 100644
--- a/gdb/cp-support.c
+++ b/gdb/cp-support.c
@@ -36,6 +36,7 @@
 #include "value.h"
 #include "cp-abi.h"
 #include "language.h"
+#include <signal.h>
 
 #include "safe-ctype.h"
 
@@ -1505,12 +1506,140 @@ cp_lookup_rtti_type (const char *name, struct block *block)
   return rtti_type;
 }
 
+#ifdef HAVE_WORKING_FORK
+
+/* If nonzero, attempt to catch crashes in the demangler and print
+   useful debugging information.  */
+
+static int catch_demangler_crashes = 1;
+
+/* Wrap set/long jmp so that it's more portable.  */
+
+#if defined(HAVE_SIGSETJMP)
+#define SIGJMP_BUF		sigjmp_buf
+#define SIGSETJMP(buf)		sigsetjmp((buf), 1)
+#define SIGLONGJMP(buf,val)	siglongjmp((buf), (val))
+#else
+#define SIGJMP_BUF		jmp_buf
+#define SIGSETJMP(buf)		setjmp(buf)
+#define SIGLONGJMP(buf,val)	longjmp((buf), (val))
+#endif
+
+/* Stack context and environment for demangler crash recovery.  */
+
+static SIGJMP_BUF gdb_demangle_jmp_buf;
+
+/* If nonzero, attempt to dump core from the signal handler.  */
+
+static int gdb_demangle_attempt_core_dump = 1;
+
+/* Signal handler for gdb_demangle.  */
+
+static void
+gdb_demangle_signal_handler (int signo)
+{
+  if (gdb_demangle_attempt_core_dump)
+    {
+      if (fork () == 0)
+	dump_core ();
+
+      gdb_demangle_attempt_core_dump = 0;
+    }
+
+  SIGLONGJMP (gdb_demangle_jmp_buf, signo);
+}
+
+#endif
+
 /* A wrapper for bfd_demangle.  */
 
 char *
 gdb_demangle (const char *name, int options)
 {
-  return bfd_demangle (NULL, name, options);
+  char *result = NULL;
+  int crash_signal = 0;
+
+#ifdef HAVE_WORKING_FORK
+#if defined (HAVE_SIGACTION) && defined (SA_RESTART)
+  struct sigaction sa, old_sa;
+#else
+  void (*ofunc) ();
+#endif
+  static int can_dump_core = -1;
+
+  if (can_dump_core == -1)
+    {
+      can_dump_core = check_can_dump_core ();
+
+      if (!can_dump_core)
+	gdb_demangle_attempt_core_dump = 0;
+    }
+
+  if (catch_demangler_crashes)
+    {
+#if defined (HAVE_SIGACTION) && defined (SA_RESTART)
+      sa.sa_handler = gdb_demangle_signal_handler;
+      sigemptyset (&sa.sa_mask);
+      sa.sa_flags = SA_ONSTACK;
+      sigaction (SIGSEGV, &sa, &old_sa);
+#else
+      ofunc = (void (*)()) signal (SIGSEGV, gdb_demangle_signal_handler);
+#endif
+
+      crash_signal = SIGSETJMP (gdb_demangle_jmp_buf);
+    }
+#endif
+
+  if (crash_signal == 0)
+    result = bfd_demangle (NULL, name, options);
+
+#ifdef HAVE_WORKING_FORK
+  if (catch_demangler_crashes)
+    {
+#if defined (HAVE_SIGACTION) && defined (SA_RESTART)
+      sigaction (SIGSEGV, &old_sa, NULL);
+#else
+      signal (SIGSEGV, ofunc);
+#endif
+
+      if (crash_signal != 0)
+	{
+	  static int error_reported = 0;
+
+	  if (!error_reported)
+	    {
+	      char *dmw_msg;
+	      struct cleanup *back_to;
+
+	      dmw_msg = xstrprintf (_("unable to demangle '%s' "
+				      "(demangler failed with signal %d)"),
+				    name, crash_signal);
+	      back_to = make_cleanup (xfree, dmw_msg);
+
+	      if (!can_dump_core)
+		{
+		  char *cdc_msg = xstrprintf ("%s:%d: %s: %s",
+					      __FILE__, __LINE__,
+					      "demangler-warning",
+					      dmw_msg);
+
+		  make_cleanup (xfree, cdc_msg);
+		  warn_cant_dump_core (cdc_msg);
+		}
+
+	      demangler_warning (__FILE__, __LINE__, "%s", dmw_msg);
+
+	      do_cleanups (back_to);
+
+	      error_reported = 1;
+	    }
+
+	  result = NULL;
+	}
+    }
+#endif
+
+  return result;
 }
 
 /* Don't allow just "maintenance cplus".  */
@@ -1585,4 +1714,17 @@ _initialize_cp_support (void)
 Usage: info vtbl EXPRESSION\n\
 Evaluate EXPRESSION and display the virtual function table for the\n\
 resulting object."));
+
+#ifdef HAVE_WORKING_FORK
+  add_setshow_boolean_cmd ("catch-demangler-crashes", class_maintenance,
+			   &catch_demangler_crashes, _("\
+Set whether to attempt to catch demangler crashes."), _("\
+Show whether to attempt to catch demangler crashes."), _("\
+If enabled GDB will attempt to catch demangler crashes and\n\
+display the offending symbol."),
+			   NULL,
+			   NULL,
+			   &maintenance_set_cmdlist,
+			   &maintenance_show_cmdlist);
+#endif
 }
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 9f7fa18..242117b 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -33235,6 +33235,17 @@ Expand symbol tables.
 If @var{regexp} is specified, only expand symbol tables for file
 names matching @var{regexp}.
 
+@kindex maint set catch-demangler-crashes
+@kindex maint show catch-demangler-crashes
+@cindex demangler crashes
+@item maint set catch-demangler-crashes [on|off]
+@itemx maint show catch-demangler-crashes
+Control whether @value{GDBN} should attempt to catch crashes in the
+symbol name demangler.  The default is to attempt to catch crashes.
+If enabled, the first time a crash is caught, a core file is created,
+the offending symbol is displayed and the user is presented with the
+option to terminate the current session.
+
 @kindex maint cplus first_component
 @item maint cplus first_component @var{name}
 Print the first C@t{++} class/namespace component of @var{name}.