Re: [RFC] Patch for gnats pr 2495

[Phil Muldoon <pmuldoon at redhat dot com>]

Tom Tromey wrote:
> > > > > > "Phil" == Phil Muldoon <pmuldoon@redhat.com> writes:
> > > > > >             
>
> Phil> This patch addresses that by gating access to std::terminate in an
> Phil> inferior function call.
>
> Sounds good.  The patch looks nice!  In fact the majority of my
> comments are on the string constants :-

I've attached an updated patch. I think I caught all of your suggestions.

gdb/doc/ChangeLog
2008-10-22  Phil Muldoon  <pmuldoon@redhat.com>

       * gdb.texinfo (Calling): Add unwind-on-terminating-exception
       flag descriptions.

gdb/ChangeLog
2008-10-22  Phil Muldoon  <pmuldoon@redhat.com>

  * infcall.c (show_unwind_on_terminating_exception_p): New
  function.
  (call_function_by_hand): Create breakpoint and clean-up call for
  std::terminate.breakpoint. Add unwind_on_terminating_exception_p
  gate. Pop frame on breakpoint hit.
  (_initialize_infcall): Add add_setshow_boolean_cmd for
  unwind-on-terminating-exception.

gdb/testsuite/ChangeLog
2008-10-22  Phil Muldoon  <pmuldoon@redhat.com>

  * gdb.cp/gdb2495.cc: New file.
  * gdb.cp/gdb2495.exp: New file.



diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 67b5fac..1703c27 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -12169,6 +12169,12 @@ It is possible for the function you call via the @code{print} or
 the function, or if you passed it incorrect arguments).  What happens
 in that case is controlled by the @code{set unwindonsignal} command.
 
+Similarly, with a C++ program  it is possible for the function you
+call via the @code{print} or @code{call} command to generate an
+exception that is not handled due to the constraints of the dummy
+frame. What happens in that case is controlled by the  
+@code{set unwind-on-terminating-exception} command.
+
 @table @code
 @item set unwindonsignal
 @kindex set unwindonsignal
@@ -12185,6 +12191,23 @@ received.
 @kindex show unwindonsignal
 Show the current setting of stack unwinding in the functions called by
 @value{GDBN}.
+
+@item set unwind-on-terminating-exception
+@kindex set unwind-on-terminating-exception
+@cindex unwind stack in called functions
+@cindex call dummy stack unwinding on unhandled exception.
+Set unwinding of the stack if a C++ exception is raised but unhandled  
+while in a function that @value{GDBN} called in the program being
+debugged.  If set to on (the default), @value{GDBN} unwinds the stack
+it created for the call and restores the context to what it was before
+the call.  If set to off, @value{GDBN} the exception is delivered to
+the default C++ exception handler.
+
+@item show unwind-on-terminating-exception
+@kindex show unwind-on-terminating-exception
+Show the current setting of stack unwinding in the functions called by
+@value{GDBN}.
+
 @end table
 
 @cindex weak alias functions
diff --git a/gdb/infcall.c b/gdb/infcall.c
index 5cc068a..5749d20 100644
--- a/gdb/infcall.c
+++ b/gdb/infcall.c
@@ -91,6 +91,28 @@ Unwinding of stack if a signal is received while in a call dummy is %s.\n"),
 		    value);
 }
 
+/* This boolean tells what gdb should do if a std::terminate call is
+   made while in a function called from gdb (call dummy).  
+   As the confines of a single dummy stack prohibit out-of-frame
+   handlers from handling a raised exception, and as out-of-frame
+   handlers are common in C++, this can lead to no handler being found
+   by the unwinder, and a std::terminate call. This is a false positive.
+   If set, gdb unwinds the stack and restores the context to what it 
+   was before the call.
+
+   The default is to unwind the frame if a std::terminate call is made.. */
+
+static int unwind_on_terminating_exception_p = 1;
+static void
+show_unwind_on_terminating_exception_p (struct ui_file *file, int from_tty,
+					struct cmd_list_element *c,
+					const char *value)
+
+{
+  fprintf_filtered (file, _("\
+Unwind stack if a C++ exception is unhandled while in a call dummy is %s.\n"),
+		    value);
+}
 
 /* Perform the standard coercions that are specified
    for arguments to be passed to C or Ada functions.
@@ -328,6 +350,8 @@ call_function_by_hand (struct value *function, int nargs, struct value **args)
   struct cleanup *args_cleanup;
   struct frame_info *frame;
   struct gdbarch *gdbarch;
+  struct breakpoint *terminate_bp = 0;
+  struct minimal_symbol *tm;
 
   if (TYPE_CODE (ftype) == TYPE_CODE_PTR)
     ftype = check_typedef (TYPE_TARGET_TYPE (ftype));
@@ -652,6 +676,27 @@ call_function_by_hand (struct value *function, int nargs, struct value **args)
   /* Now proceed, having reached the desired place.  */
   clear_proceed_status ();
     
+  /* Create a breakpoint in std::terminate. 
+     If a C++ exception is raised in the dummy-frame, and the 
+     exception handler is (normally, and expected to be) out-of-frame, 
+     the default C++ handler will (wrongly) be called in an inferior
+     function call.  This is wrong, as an exception can be  normally
+     and legally handled out-of-frame. The confines of the dummy frame
+     prevent the unwinder from finding the correct handler (or any
+     handler, unless it is in-frame). The default handler calls
+     std::terminate. This will kill the inferior. Assert that
+     terminate should never be called in an inferior function
+     call. Place a momentary breakpoint in the std::terminate function
+     and if triggered in the call, rewind */
+  if (unwind_on_terminating_exception_p)
+    {
+      tm = lookup_minimal_symbol ("std::terminate()", NULL, NULL); 
+      if (tm != NULL)
+	terminate_bp = set_momentary_breakpoint_at_pc
+	  (SYMBOL_VALUE_ADDRESS (tm),  bp_breakpoint);
+      make_cleanup_delete_breakpoint (terminate_bp);
+    }
+  
   /* Execute a "stack dummy", a piece of code stored in the stack by
      the debugger to be executed in the inferior.
 
@@ -778,6 +823,30 @@ Evaluation of the expression containing the function (%s) will be abandoned."),
 	     previously selected frame), would write the registers
 	     from the inf_status (which is wrong), and would do other
 	     wrong things.  */
+
+	  /* Check if unwind on terminating exception behaviour is on */
+	  if (unwind_on_terminating_exception_p)
+	    {
+	      /* Check that the breakpoint is our special std::terminate
+	     breakpoint. If it is, we do not want to kill the inferior
+	     in an inferior function call. Rewind, and warn the user */
+
+	      if ((terminate_bp != NULL) &&
+		  (inferior_thread()->stop_bpstat->breakpoint_at->address
+		   == terminate_bp->loc->address)) 
+		
+		
+		{
+		  frame_pop (get_current_frame ());
+		  error (_("\
+The program being debugged entered a std::terminate call which would\n\
+have terminated the program being debugged.  GDB has restored the\n\
+context to what it was before the call.\n\
+To change this behaviour use \"set unwind-on-terminating-exception off\"\n\
+Evaluation of the expression containing the function (%s) will be abandoned."), 
+			 name);
+		}
+	    } 
 	  discard_cleanups (inf_status_cleanup);
 	  discard_inferior_status (inf_status);
 	  /* The following error message used to say "The expression
@@ -878,4 +947,19 @@ The default is to stop in the frame where the signal was received."),
 			   NULL,
 			   show_unwind_on_signal_p,
 			   &setlist, &showlist);
+
+  add_setshow_boolean_cmd ("unwind-on-terminating-exception", no_class,
+			   &unwind_on_terminating_exception_p, _("\
+Set unwinding of stack if a std::terminate() call originates from\n\
+the default C++ exception handler."), _("\
+Show unwinding of stack if a std::terminate() call originates from\n\
+the default C++ exception handler."), _("\
+The unwind on terminating exception flag lets the user determine\n\
+what gdb should do if a std::terminate() call is made from the\n\
+default exception handler.\n\
+The default is to unwind the frame."),
+			   NULL,
+			   show_unwind_on_terminating_exception_p,
+			   &setlist, &showlist);
+
 }
diff --git a/gdb/testsuite/gdb.cp/Makefile.in b/gdb/testsuite/gdb.cp/Makefile.in
index f4a989c..6d0f809 100644
--- a/gdb/testsuite/gdb.cp/Makefile.in
+++ b/gdb/testsuite/gdb.cp/Makefile.in
@@ -4,7 +4,7 @@ srcdir = @srcdir@
 EXECUTABLES = ambiguous annota2 anon-union cplusfuncs cttiadd \
 	derivation inherit local member-ptr method misc \
         overload ovldbreak ref-typ ref-typ2 templates userdef virtfunc namespace \
-	ref-types ref-params method2
+	ref-types ref-params method2 gdb2495
 
 all info install-info dvi install uninstall installcheck check:
 	@echo "Nothing to be done for $@..."
diff --git a/gdb/testsuite/gdb.cp/gdb2495.cc b/gdb/testsuite/gdb.cp/gdb2495.cc
new file mode 100644
index 0000000..4df265f
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/gdb2495.cc
@@ -0,0 +1,90 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2008 Free Software Foundation, Inc.
+
+   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; either version 3 of the License, or
+   (at your option) any later version.
+
+   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, see <http://www.gnu.org/licenses/>.
+   */
+
+#include <iostream>
+#include <signal.h>
+
+using namespace std;
+
+class SimpleException 
+{
+
+public:
+
+  void raise_signal (int dummy) 
+  {
+    if (dummy > 0)
+      raise(SIGABRT);
+  }
+
+  int  no_throw_function () 
+  {
+    return 1;
+  }
+  
+  void throw_function () 
+  {
+    throw 1;
+  }
+  
+  int throw_function_with_handler () 
+  {
+    try
+      {
+	throw 1;
+      }
+    catch (...)
+      {
+	cout << "Handled" << endl;
+      } 
+    
+    return 2;
+  }
+  
+  void call_throw_function_no_handler () 
+  {
+    throw_function ();
+  }
+  
+  void call_throw_function_handler () 
+  {
+    throw_function_with_handler ();
+  }
+};
+SimpleException exceptions;
+
+int 
+main()
+{
+  // Have to call all these functions
+  // so not optimized away.
+  exceptions.raise_signal (-1);
+  exceptions.no_throw_function ();
+  exceptions.throw_function_with_handler ();
+  exceptions.call_throw_function_handler ();
+  try 
+    {
+      exceptions.throw_function ();
+      exceptions.call_throw_function_no_handler ();
+    }
+  catch (...)
+    {
+    }
+  return 0;
+}
+
diff --git a/gdb/testsuite/gdb.cp/gdb2495.exp b/gdb/testsuite/gdb.cp/gdb2495.exp
new file mode 100644
index 0000000..5afeb1b
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/gdb2495.exp
@@ -0,0 +1,160 @@
+# Copyright 2008 Free Software Foundation, Inc.
+
+# 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; either version 3 of the License, or
+# (at your option) any later version.
+#
+# 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, see <http://www.gnu.org/licenses/>.
+
+
+# In gdb inferior function calls, if a C++ exception is raised in the
+# dummy-frame, and the exception handler is (normally, and expected to
+# be) out-of-frame, the default C++ handler will (wrongly) be called
+# in an inferior function call.  
+# This is incorrect as an exception can normally and legally be handled
+# out-of-frame. The confines of the dummy frame prevent the unwinder
+# from finding the correct handler (or any handler, unless it is
+# in-frame). The default handler calls std::terminate. This will kill
+# the inferior. Assert that terminate should never be called in an
+# inferior function call. These tests test the functionality around
+# unwinding that sequence and also tests the flag behaviour gating this
+# functionality.
+
+# This test is largley based off gdb.base/callfuncs.exp.
+
+if $tracelevel then {
+    strace $tracelevel
+}
+
+if { [skip_cplus_tests] } { continue }
+
+set prms_id 2495
+set bug_id 0
+
+set testfile "gdb2495"
+set srcfile ${testfile}.cc
+set binfile $objdir/$subdir/$testfile
+
+# Create and source the file that provides information about the compiler
+# used to compile the test case.
+if [get_compiler_info ${binfile} "c++"] {
+    return -1
+}
+
+if { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug c++}] != "" } {
+     untested gdb2495.exp
+     return -1
+}
+
+# Some targets can't do function calls, so don't even bother with this
+# test.
+if [target_info exists gdb,cannot_call_functions] {
+    setup_xfail "*-*-*" 2416
+    fail "This target can not call functions"
+    continue
+}
+
+gdb_exit
+gdb_start
+gdb_reinitialize_dir $srcdir/$subdir
+gdb_load ${binfile}
+
+if ![runto_main] then {
+    perror "couldn't run to main"
+    continue
+} 
+
+# See http://sources.redhat.com/gdb/bugs/2495
+
+# Test normal baseline behaviour. Call a function that
+# does not raise an exception ...
+gdb_test "p exceptions.no_throw_function()" " = 1"
+# And one that does but handles it in-frame ...
+gdb_test "p exceptions.throw_function_with_handler()" " = 2"
+# Both should return normally.
+
+# Test basic unwind. Call a function that raises an exception but
+# does not handle it. It should be rewound ...
+gdb_test "p exceptions.throw_function()" \
+    "The program being debugged entered a std::terminate call .*" \
+    "Call a function that raises an exception without a handler."
+
+# Make sure that after rewinding we are back at the call parent.
+gdb_test "bt" \
+    "#0  main.*" \
+    "bt after returning from a popped frame"
+
+# Make sure the only breakpoint is the one set via the runto_main
+# call and that the std::terminate breakpoint has evaporated and
+# cleaned-up.
+gdb_test "info breakpoints" \
+    "gdb.cp/gdb2495\.cc.*"
+
+# Turn off this new behaviour ...
+send_gdb "set unwind-on-terminating-exception off\n" 
+gdb_expect {
+    -re "$gdb_prompt $" {pass "set unwind-on-terminating-exception"}
+    timeout {fail "(timeout) set  unwind-on-terminating-exception"}
+}
+
+# Check that it is turned off ...
+gdb_test "show unwind-on-terminating-exception" \
+    "exception is unhandled while in a call dummy is off.*" \
+    "Turn off unwind on terminating exception flag"
+
+# Check that the old behaviour is restored.
+gdb_test "p exceptions.throw_function()" \
+    "The program being debugged was signaled while in a function .*" \
+    "Call a function that raises an exception with unwinding off.."
+
+
+# Restart back at main
+if ![runto_main] then {
+    perror "couldn't run to main"
+    continue
+} 
+
+
+# Check to see if our new behaviour alters the unwind signal
+# behaviour. It should not. Test both on and off states.
+
+# Turn on unwind on signal  behaviour ...
+send_gdb "set unwindonsignal on\n" 
+gdb_expect {
+    -re "$gdb_prompt $" {pass "set unwindonsignal on"}
+    timeout {fail "(timeout) set  unwindonsignal on"}
+}
+
+# Check that it is turned on ...
+gdb_test "show unwindonsignal" \
+    "signal is received while in a call dummy is on.*" \
+    "Turn on unwind on signal"
+
+# Check to see if new behaviour interferes with
+# normal signal handling in inferior function calls.
+gdb_test "p exceptions.raise_signal(1)" \
+    "To change this behavior use \"set unwindonsignal off\".*"
+
+# And reverse. Turn off
+send_gdb "set unwindonsignal off\n" 
+gdb_expect {
+    -re "$gdb_prompt $" {pass "set unwindonsignal off"}
+    timeout {fail "(timeout) set  unwindonsignal off"}
+}
+
+# Check that it is turned off ...
+gdb_test "show unwindonsignal" \
+    "signal is received while in a call dummy is off.*" \
+    "Turn off unwind on signal"
+
+# Check to see if new behaviour interferes with
+# normal signal handling in inferior function calls.
+gdb_test "p exceptions.raise_signal(1)" \
+    "To change this behavior use \"set unwindonsignal on\".*"