(Ada) New command to stop at start of exception handler.

When using gdb for debugging Ada source code, there are several catchpoint
types you can define in order to stop upon certain conditions.  Let's
use this small example:

procedure Foo is
begin
   begin
      raise Constraint_Error;
   exception
      when Program_Error =>
         null;
      when Constraint_Error =>
         null;
      when others =>
         null;
   end;
end Foo;

One can stop when the exception is being raised by using the exception
catchpoint like below:

(gdb) catch exception
Catchpoint 1: all Ada exceptions
(gdb)

In that case, when running Foo, gdb will stop at the line where the exception
was raised:

   begin
>>>   raise Constraint_Error;
   exception

This patch introduces new type of catchpoint, when the user wants to stop
at the location of the exception handling.
Imagine we want to stop on any exception handled by the program, we can do:

(gdb) catch handlers
Catchpoint 1: all Ada exceptions handlers
(gdb) r
Starting program: /tmp/foo

By doing so, when running Foo, gdb will stop here:

Catchpoint 1, exception at 0x000000000040255a in foo () at foo.adb:25
25          when Constraint_Error =>
(gdb)

It is also possible to stop when the Constraint_Error exception is being
handled in this program.  With this patch, we can use:

(gdb) catch handlers Constraint_Error
Catchpoint 1: `Constraint_Error' Ada exception handlers
(gdb)

Like for other catchpoint, you can set a condition when adding a catchpoint
on exception handlers.
Here the handlers catchpoint checks Global_Var:

(gdb) catch handlers Constraint_Error if Global_Var /= 0

gdb/ChangeLog:

        * ada-lang.h (ada_exception_catchpoint_kind) <ada_catch_handlers>:
        Add field.
        * ada-lang.c (struct exception_support_info) <catch_handlers_sym>:
        Add field.
        (default_exception_support_info) <catch_handlers_sym>: Add field.
        (exception_support_info_fallback) <catch_handlers_sym>: Add field.
        (ada_exception_name_addr_1): Add "catch handlers" handling.
        (ada_exception_catchpoint_cond_string) <ex>: New parameter.
        Update all callers.
        (create_excep_cond_exprs) <ex>: Add parameter.
        (re_set_exception): Update create_excep_cond_exprs call.
        (print_it_exception, print_one_exception, print_mention_exception)
        (print_recreate_exception): Add "catch handler" handling.
        (allocate_location_catch_handlers, re_set_catch_handlers)
        (check_status_catch_handlers, print_it_catch_handlers)
        (print_one_catch_handlers, print_mention_catch_handlers)
        (print_recreate_catch_handlers): New function.
        (catch_handlers_breakpoint_ops): New variable.
        (catch_ada_exception_command_split) <is_catch_handlers_cmd>:
        Add parameter.  Add "catch handler" handling.
        (ada_exception_sym_name, ada_exception_breakpoint_ops):
        Add "catch handler" handling.
        (ada_exception_catchpoint_cond_string): Add "catch handler"
        handling.
        (create_ada_exception_catchpoint): Update create_excep_cond_exprs
        call.
        (catch_ada_handlers_command): New function.
        (initialize_ada_catchpoint_ops): Initialize "catch handlers"
        operations structure.
        (_initialize_ada_language): Add "catch handlers" command entry.
        * NEWS: Document "catch handlers" feature.

gdb/doc/ChangeLog:

        * gdb.texinfo (Set Catchpoints): Add documentation for new
        "catch handlers" action.

gdb/testsuite/ChangeLog:

        * gdb.ada/excep_handle.exp: New testcase.
        * gdb.ada/excep_handle/foo.adb: New file.
        * gdb.ada/excep_handle/pck.ads: New file.

Tested on x86_64-linux.

1 files changed, 184 insertions, 13 deletions

diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
index 851e69a..4ecf7b0 100644
--- a/gdb/ada-lang.c
+++ b/gdb/ada-lang.c
@@ -12024,6 +12024,10 @@ struct exception_support_info
       a catchpoint on failed assertions.  */
    const char *catch_assert_sym;
 
+   /* The name of the symbol to break on in order to insert
+      a catchpoint on exception handling.  */
+   const char *catch_handlers_sym;
+
    /* Assuming that the inferior just triggered an unhandled exception
       catchpoint, this function is responsible for returning the address
       in inferior memory where the name of that exception is stored.
@@ -12043,6 +12047,7 @@ static const struct exception_support_info default_exception_support_info =
   "__gnat_debug_raise_exception", /* catch_exception_sym */
   "__gnat_unhandled_exception", /* catch_exception_unhandled_sym */
   "__gnat_debug_raise_assert_failure", /* catch_assert_sym */
+  "__gnat_begin_handler", /* catch_handlers_sym */
   ada_unhandled_exception_name_addr
 };
 
@@ -12055,6 +12060,7 @@ static const struct exception_support_info exception_support_info_fallback =
   "__gnat_raise_nodefer_with_msg", /* catch_exception_sym */
   "__gnat_unhandled_exception", /* catch_exception_unhandled_sym */
   "system__assertions__raise_assert_failure",  /* catch_assert_sym */
+  "__gnat_begin_handler", /* catch_handlers_sym */
   ada_unhandled_exception_name_addr_from_raise
 };
 
@@ -12323,7 +12329,12 @@ ada_exception_name_addr_1 (enum ada_exception_catchpoint_kind ex,
       case ada_catch_exception_unhandled:
         return data->exception_info->unhandled_exception_name_addr ();
         break;
-      
+
+      case ada_catch_handlers:
+        return 0;  /* The runtimes does not provide access to the exception
+		      name.  */
+        break;
+
       case ada_catch_assert:
         return 0;  /* Exception name is not relevant in this case.  */
         break;
@@ -12429,7 +12440,9 @@ ada_exception_name_addr (enum ada_exception_catchpoint_kind ex,
   return result;
 }
 
-static char *ada_exception_catchpoint_cond_string (const char *excep_string);
+static char *ada_exception_catchpoint_cond_string
+  (const char *excep_string,
+   enum ada_exception_catchpoint_kind ex);
 
 /* Ada catchpoints.
 
@@ -12492,7 +12505,8 @@ struct ada_catchpoint : public breakpoint
    catchpoint's locations, and store them for later evaluation.  */
 
 static void
-create_excep_cond_exprs (struct ada_catchpoint *c)
+create_excep_cond_exprs (struct ada_catchpoint *c,
+                         enum ada_exception_catchpoint_kind ex)
 {
   struct cleanup *old_chain;
   struct bp_location *bl;
@@ -12508,7 +12522,7 @@ create_excep_cond_exprs (struct ada_catchpoint *c)
 
   /* Compute the condition expression in text form, from the specific
      expection we want to catch.  */
-  cond_string = ada_exception_catchpoint_cond_string (c->excep_string);
+  cond_string = ada_exception_catchpoint_cond_string (c->excep_string, ex);
   old_chain = make_cleanup (xfree, cond_string);
 
   /* Iterate over all the catchpoint's locations, and parse an
@@ -12576,7 +12590,7 @@ re_set_exception (enum ada_exception_catchpoint_kind ex, struct breakpoint *b)
 
   /* Reparse the exception conditional expressions.  One for each
      location.  */
-  create_excep_cond_exprs (c);
+  create_excep_cond_exprs (c, ex);
 }
 
 /* Returns true if we should stop for this breakpoint hit.  If the
@@ -12665,6 +12679,7 @@ print_it_exception (enum ada_exception_catchpoint_kind ex, bpstat bs)
     {
       case ada_catch_exception:
       case ada_catch_exception_unhandled:
+      case ada_catch_handlers:
 	{
 	  const CORE_ADDR addr = ada_exception_name_addr (ex, b);
 	  char exception_name[256];
@@ -12762,6 +12777,17 @@ print_one_exception (enum ada_exception_catchpoint_kind ex,
         uiout->field_string ("what", "unhandled Ada exceptions");
         break;
       
+      case ada_catch_handlers:
+        if (c->excep_string != NULL)
+          {
+	    uiout->field_fmt ("what",
+			      _("`%s' Ada exception handlers"),
+			      c->excep_string);
+          }
+        else
+	  uiout->field_string ("what", "all Ada exceptions handlers");
+        break;
+
       case ada_catch_assert:
         uiout->field_string ("what", "failed Ada assertions");
         break;
@@ -12805,7 +12831,19 @@ print_mention_exception (enum ada_exception_catchpoint_kind ex,
       case ada_catch_exception_unhandled:
         uiout->text (_("unhandled Ada exceptions"));
         break;
-      
+
+      case ada_catch_handlers:
+        if (c->excep_string != NULL)
+	  {
+	    std::string info
+	      = string_printf (_("`%s' Ada exception handlers"),
+			       c->excep_string);
+	    uiout->text (info.c_str ());
+	  }
+        else
+          uiout->text (_("all Ada exceptions handlers"));
+        break;
+
       case ada_catch_assert:
         uiout->text (_("failed Ada assertions"));
         break;
@@ -12837,6 +12875,10 @@ print_recreate_exception (enum ada_exception_catchpoint_kind ex,
 	fprintf_filtered (fp, "catch exception unhandled");
 	break;
 
+      case ada_catch_handlers:
+	fprintf_filtered (fp, "catch handlers");
+	break;
+
       case ada_catch_assert:
 	fprintf_filtered (fp, "catch assert");
 	break;
@@ -12987,6 +13029,54 @@ print_recreate_catch_assert (struct breakpoint *b, struct ui_file *fp)
 
 static struct breakpoint_ops catch_assert_breakpoint_ops;
 
+/* Virtual table for "catch handlers" breakpoints.  */
+
+static struct bp_location *
+allocate_location_catch_handlers (struct breakpoint *self)
+{
+  return allocate_location_exception (ada_catch_handlers, self);
+}
+
+static void
+re_set_catch_handlers (struct breakpoint *b)
+{
+  re_set_exception (ada_catch_handlers, b);
+}
+
+static void
+check_status_catch_handlers (bpstat bs)
+{
+  check_status_exception (ada_catch_handlers, bs);
+}
+
+static enum print_stop_action
+print_it_catch_handlers (bpstat bs)
+{
+  return print_it_exception (ada_catch_handlers, bs);
+}
+
+static void
+print_one_catch_handlers (struct breakpoint *b,
+			  struct bp_location **last_loc)
+{
+  print_one_exception (ada_catch_handlers, b, last_loc);
+}
+
+static void
+print_mention_catch_handlers (struct breakpoint *b)
+{
+  print_mention_exception (ada_catch_handlers, b);
+}
+
+static void
+print_recreate_catch_handlers (struct breakpoint *b,
+			       struct ui_file *fp)
+{
+  print_recreate_exception (ada_catch_handlers, b, fp);
+}
+
+static struct breakpoint_ops catch_handlers_breakpoint_ops;
+
 /* Return a newly allocated copy of the first space-separated token
    in ARGSP, and then adjust ARGSP to point immediately after that
    token.
@@ -13025,12 +13115,15 @@ ada_get_next_arg (const char **argsp)
    Set EX to the appropriate catchpoint type.
    Set EXCEP_STRING to the name of the specific exception if
    specified by the user.
+   IS_CATCH_HANDLERS_CMD: True if the arguments are for a
+   "catch handlers" command.  False otherwise.
    If a condition is found at the end of the arguments, the condition
    expression is stored in COND_STRING (memory must be deallocated
    after use).  Otherwise COND_STRING is set to NULL.  */
 
 static void
 catch_ada_exception_command_split (const char *args,
+				   bool is_catch_handlers_cmd,
                                    enum ada_exception_catchpoint_kind *ex,
 				   char **excep_string,
 				   char **cond_string)
@@ -13076,7 +13169,13 @@ catch_ada_exception_command_split (const char *args,
 
   discard_cleanups (old_chain);
 
-  if (exception_name == NULL)
+  if (is_catch_handlers_cmd)
+    {
+      /* Catch handling of exceptions.  */
+      *ex = ada_catch_handlers;
+      *excep_string = exception_name;
+    }
+  else if (exception_name == NULL)
     {
       /* Catch all exceptions.  */
       *ex = ada_catch_exception;
@@ -13118,6 +13217,9 @@ ada_exception_sym_name (enum ada_exception_catchpoint_kind ex)
       case ada_catch_assert:
         return (data->exception_info->catch_assert_sym);
         break;
+      case ada_catch_handlers:
+        return (data->exception_info->catch_handlers_sym);
+        break;
       default:
         internal_error (__FILE__, __LINE__,
                         _("unexpected catchpoint kind (%d)"), ex);
@@ -13141,6 +13243,9 @@ ada_exception_breakpoint_ops (enum ada_exception_catchpoint_kind ex)
       case ada_catch_assert:
         return (&catch_assert_breakpoint_ops);
         break;
+      case ada_catch_handlers:
+        return (&catch_handlers_breakpoint_ops);
+        break;
       default:
         internal_error (__FILE__, __LINE__,
                         _("unexpected catchpoint kind (%d)"), ex);
@@ -13151,14 +13256,29 @@ ada_exception_breakpoint_ops (enum ada_exception_catchpoint_kind ex)
    being raised with the exception that the user wants to catch.  This
    assumes that this condition is used when the inferior just triggered
    an exception catchpoint.
+   EX: the type of catchpoints used for catching Ada exceptions.
    
    The string returned is a newly allocated string that needs to be
    deallocated later.  */
 
 static char *
-ada_exception_catchpoint_cond_string (const char *excep_string)
+ada_exception_catchpoint_cond_string (const char *excep_string,
+                                      enum ada_exception_catchpoint_kind ex)
 {
   int i;
+  bool is_standard_exc = false;
+  const char *actual_exc_expr;
+  char *ref_exc_expr;
+
+  if (ex == ada_catch_handlers)
+    {
+      /* For exception handlers catchpoints, the condition string does
+         not use the same parameter as for the other exceptions.  */
+      actual_exc_expr = ("long_integer (GNAT_GCC_exception_Access"
+			 "(gcc_exception).all.occurrence.id)");
+    }
+  else
+    actual_exc_expr = "long_integer (e)";
 
   /* The standard exceptions are a special case.  They are defined in
      runtime units that have been compiled without debugging info; if
@@ -13183,11 +13303,19 @@ ada_exception_catchpoint_cond_string (const char *excep_string)
     {
       if (strcmp (standard_exc [i], excep_string) == 0)
 	{
-          return xstrprintf ("long_integer (e) = long_integer (&standard.%s)",
-                             excep_string);
+	  is_standard_exc = true;
+	  break;
 	}
     }
-  return xstrprintf ("long_integer (e) = long_integer (&%s)", excep_string);
+
+  if (is_standard_exc)
+    ref_exc_expr = xstrprintf ("long_integer (&standard.%s)", excep_string);
+  else
+    ref_exc_expr = xstrprintf ("long_integer (&%s)", excep_string);
+
+  char *result =  xstrprintf ("%s = %s", actual_exc_expr, ref_exc_expr);
+  xfree (ref_exc_expr);
+  return result;
 }
 
 /* Return the symtab_and_line that should be used to insert an exception
@@ -13270,7 +13398,7 @@ create_ada_exception_catchpoint (struct gdbarch *gdbarch,
   init_ada_exception_breakpoint (c.get (), gdbarch, sal, addr_string,
 				 ops, tempflag, disabled, from_tty);
   c->excep_string = excep_string;
-  create_excep_cond_exprs (c.get ());
+  create_excep_cond_exprs (c.get (), ex_kind);
   if (cond_string != NULL)
     set_breakpoint_condition (c.get (), cond_string, from_tty);
   install_breakpoint (0, std::move (c), 1);
@@ -13293,7 +13421,32 @@ catch_ada_exception_command (const char *arg_entry, int from_tty,
 
   if (!arg)
     arg = "";
-  catch_ada_exception_command_split (arg, &ex_kind, &excep_string,
+  catch_ada_exception_command_split (arg, false, &ex_kind, &excep_string,
+				     &cond_string);
+  create_ada_exception_catchpoint (gdbarch, ex_kind,
+				   excep_string, cond_string,
+				   tempflag, 1 /* enabled */,
+				   from_tty);
+}
+
+/* Implement the "catch handlers" command.  */
+
+static void
+catch_ada_handlers_command (const char *arg_entry, int from_tty,
+			    struct cmd_list_element *command)
+{
+  const char *arg = arg_entry;
+  struct gdbarch *gdbarch = get_current_arch ();
+  int tempflag;
+  enum ada_exception_catchpoint_kind ex_kind;
+  char *excep_string = NULL;
+  char *cond_string = NULL;
+
+  tempflag = get_cmd_context (command) == CATCH_TEMPORARY;
+
+  if (!arg)
+    arg = "";
+  catch_ada_exception_command_split (arg, true, &ex_kind, &excep_string,
 				     &cond_string);
   create_ada_exception_catchpoint (gdbarch, ex_kind,
 				   excep_string, cond_string,
@@ -14408,6 +14561,16 @@ initialize_ada_catchpoint_ops (void)
   ops->print_one = print_one_catch_assert;
   ops->print_mention = print_mention_catch_assert;
   ops->print_recreate = print_recreate_catch_assert;
+
+  ops = &catch_handlers_breakpoint_ops;
+  *ops = bkpt_breakpoint_ops;
+  ops->allocate_location = allocate_location_catch_handlers;
+  ops->re_set = re_set_catch_handlers;
+  ops->check_status = check_status_catch_handlers;
+  ops->print_it = print_it_catch_handlers;
+  ops->print_one = print_one_catch_handlers;
+  ops->print_mention = print_mention_catch_handlers;
+  ops->print_recreate = print_recreate_catch_handlers;
 }
 
 /* This module's 'new_objfile' observer.  */
@@ -14468,6 +14631,14 @@ With an argument, catch only exceptions with the given name."),
                      NULL,
 		     CATCH_PERMANENT,
 		     CATCH_TEMPORARY);
+
+  add_catch_command ("handlers", _("\
+Catch Ada exceptions, when handled.\n\
+With an argument, catch only exceptions with the given name."),
+		     catch_ada_handlers_command,
+                     NULL,
+		     CATCH_PERMANENT,
+		     CATCH_TEMPORARY);
   add_catch_command ("assert", _("\
 Catch failed Ada assertions, when raised.\n\
 With an argument, catch only exceptions with the given name."),