Re: [RFA/doco] (Ada) provide the exception message when hitting an exception catchpoint

[Joel Brobecker <brobecker at adacore dot com>]

Hi Eli,

Would you have some time to review the doc changes in the patches
below?

Thanks!

On Fri, Nov 17, 2017 at 04:20:46PM -0500, Joel Brobecker wrote:
> Hello,
> 
> This patch enhances the debugger to print the exception message, when
> available, as part of an exception catchpoint hit notification (both
> GDB/CLI and GDB/MI). For instance, with the following code...
> 
>     procedure A is
>     begin
>        raise Constraint_Error with "hello world";
>     end A;
> 
> ... instead of printing...
> 
>     Catchpoint 1, CONSTRAINT_ERROR at 0x000000000040245c in a () at a.adb:3
> 
> ... it now prints:
> 
>     Catchpoint 1, CONSTRAINT_ERROR (hello world) at 0x000000000040245c in a ()
>                                    ^^^^^^^^^^^^^
> 
> This enhancement requires runtime support. If not present, the debugger
> just behaves as before.
> 
> In GDB/MI mode, if the exception message is available, it is provided
> as an extra field named "exception-message" in the catchpoint notification:
> 
>     *stopped,bkptno="1",[...],exception-name="CONSTRAINT_ERROR",
>        exception-message="hello world",[...]
> 
> gdb/ChangeLog:
> 
>         * ada-lang.c (ada_exception_message_1, ada_exception_message):
>         New functions.
>         (print_it_exception): If available, display the exception
>         message as well.
>         NEWS: Document new feature.
> 
> gdb/doc/ChangeLog:
> 
>         * gdb.texinfo (GDB/MI Ada Exception Information): Document
>         new "exception-message" field.
> 
> gdb/testsuite/ChangeLog:
> 
>         * gdb.ada/catch_ex.exp, gdb.ada/mi_catch_ex.exp,
>         gdb.ada/mi_ex_cond.exp: Accept optional exception message in
>         when hitting an exception catchpoint.
> 
> Tested on x86_64-linux, no regression.
> 
> Are the NEWS and doc/gdb.texinfo changes OK to commit?
> 
> Thank you,
> -- 
> Joel
> 
> ---
>  gdb/NEWS                              |  5 +++
>  gdb/ada-lang.c                        | 81 +++++++++++++++++++++++++++++++++++
>  gdb/doc/gdb.texinfo                   |  4 +-
>  gdb/testsuite/gdb.ada/catch_ex.exp    |  8 ++--
>  gdb/testsuite/gdb.ada/mi_catch_ex.exp | 10 ++---
>  gdb/testsuite/gdb.ada/mi_ex_cond.exp  |  2 +-
>  6 files changed, 99 insertions(+), 11 deletions(-)
> 
> diff --git a/gdb/NEWS b/gdb/NEWS
> index dc070fa..5928bd6 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -52,6 +52,11 @@
>       variables that are to be set or unset from GDB.  These variables
>       will affect the environment to be passed to the inferior.
>  
> +* When catching an Ada exception raised with a message, GDB now prints
> +  the message in the catchpoint hit notification. In GDB/MI mode, that
> +  information is provided as an extra field named "exception-message"
> +  in the *stopped notification.
> +
>  * New remote packets
>  
>  QEnvironmentHexEncoded
> diff --git a/gdb/ada-lang.c b/gdb/ada-lang.c
> index 33c4e8e..3265c21 100644
> --- a/gdb/ada-lang.c
> +++ b/gdb/ada-lang.c
> @@ -12105,6 +12105,73 @@ ada_exception_name_addr_1 (enum ada_exception_catchpoint_kind ex,
>    return 0; /* Should never be reached.  */
>  }
>  
> +/* Assuming the inferior is stopped at an exception catchpoint,
> +   return the message which was associated to the exception, if
> +   available.  Return NULL if the message could not be retrieved.
> +
> +   The caller must xfree the string after use.
> +
> +   Note: The exception message can be associated to an exception
> +   either through the use of the Raise_Exception function, or
> +   more simply (Ada 2005 and later), via:
> +
> +       raise Exception_Name with "exception message";
> +
> +   */
> +
> +static char *
> +ada_exception_message_1 (void)
> +{
> +  struct value *e_msg_val;
> +  char *e_msg = NULL;
> +  int e_msg_len;
> +  struct cleanup *cleanups;
> +
> +  /* For runtimes that support this feature, the exception message
> +     is passed as an unbounded string argument called "message".  */
> +  e_msg_val = parse_and_eval ("message");
> +  if (e_msg_val == NULL)
> +    return NULL; /* Exception message not supported.  */
> +
> +  e_msg_val = ada_coerce_to_simple_array (e_msg_val);
> +  gdb_assert (e_msg_val != NULL);
> +  e_msg_len = TYPE_LENGTH (value_type (e_msg_val));
> +
> +  /* If the message string is empty, then treat it as if there was
> +     no exception message.  */
> +  if (e_msg_len <= 0)
> +    return NULL;
> +
> +  e_msg = (char *) xmalloc (e_msg_len + 1);
> +  cleanups = make_cleanup (xfree, e_msg);
> +  read_memory_string (value_address (e_msg_val), e_msg, e_msg_len + 1);
> +  e_msg[e_msg_len] = '\0';
> +
> +  discard_cleanups (cleanups);
> +  return e_msg;
> +}
> +
> +/* Same as ada_exception_message_1, except that all exceptions are
> +   contained here (returning NULL instead).  */
> +
> +static char *
> +ada_exception_message (void)
> +{
> +  char *e_msg = NULL;  /* Avoid a spurious uninitialized warning.  */
> +
> +  TRY
> +    {
> +      e_msg = ada_exception_message_1 ();
> +    }
> +  CATCH (e, RETURN_MASK_ERROR)
> +    {
> +      e_msg = NULL;
> +    }
> +  END_CATCH
> +
> +  return e_msg;
> +}
> +
>  /* Same as ada_exception_name_addr_1, except that it intercepts and contains
>     any error that ada_exception_name_addr_1 might cause to be thrown.
>     When an error is intercepted, a warning with the error message is printed,
> @@ -12340,6 +12407,7 @@ print_it_exception (enum ada_exception_catchpoint_kind ex, bpstat bs)
>  {
>    struct ui_out *uiout = current_uiout;
>    struct breakpoint *b = bs->breakpoint_at;
> +  char *exception_message;
>  
>    annotate_catchpoint (b->number);
>  
> @@ -12405,6 +12473,19 @@ print_it_exception (enum ada_exception_catchpoint_kind ex, bpstat bs)
>  	uiout->text ("failed assertion");
>  	break;
>      }
> +
> +  exception_message = ada_exception_message ();
> +  if (exception_message != NULL)
> +    {
> +      struct cleanup *cleanups = make_cleanup (xfree, exception_message);
> +
> +      uiout->text (" (");
> +      uiout->field_string ("exception-message", exception_message);
> +      uiout->text (")");
> +
> +      do_cleanups (cleanups);
> +    }
> +
>    uiout->text (" at ");
>    ada_find_printable_frame (get_current_frame ());
>  
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index 29d4789..430db0f 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -27183,7 +27183,9 @@ thread was last seen on.  This field is optional.
>  Whenever a @code{*stopped} record is emitted because the program
>  stopped after hitting an exception catchpoint (@pxref{Set Catchpoints}),
>  @value{GDBN} provides the name of the exception that was raised via
> -the @code{exception-name} field.
> +the @code{exception-name} field. Also, for exceptions that were raised
> +with an exception message, @value{GDBN} provides that message via
> +the @code{exception-message} field.
>  
>  @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
>  @node GDB/MI Simple Examples
> diff --git a/gdb/testsuite/gdb.ada/catch_ex.exp b/gdb/testsuite/gdb.ada/catch_ex.exp
> index 5313e77..3797601 100644
> --- a/gdb/testsuite/gdb.ada/catch_ex.exp
> +++ b/gdb/testsuite/gdb.ada/catch_ex.exp
> @@ -62,13 +62,13 @@ gdb_test "info break" \
>           "info break, catch all Ada exceptions"
>  
>  set catchpoint_msg \
> -  "Catchpoint $any_nb, CONSTRAINT_ERROR at $any_addr in foo \\\(\\\).*at .*foo.adb:$any_nb"
> +  "Catchpoint $any_nb, CONSTRAINT_ERROR (\\\(foo\\.adb:$decimal explicit raise\\\) )?at $any_addr in foo \\\(\\\).*at .*foo.adb:$any_nb"
>  gdb_test "continue" \
>           "Continuing\.$eol$catchpoint_msg$eol.*SPOT1" \
>           "continuing to first exception"
>  
>  set catchpoint_msg \
> -  "Catchpoint $any_nb, PROGRAM_ERROR at $any_addr in foo \\\(\\\).*at .*foo.adb:$any_nb"
> +  "Catchpoint $any_nb, PROGRAM_ERROR (\\\(foo\\.adb:$decimal explicit raise\\\) )?at $any_addr in foo \\\(\\\).*at .*foo.adb:$any_nb"
>  gdb_test "continue" \
>           "Continuing\.$eol$catchpoint_msg$eol.*SPOT2" \
>           "continuing to second exception"
> @@ -116,7 +116,7 @@ gdb_test "info break" \
>           "info break, second run"
>  
>  set catchpoint_msg \
> -  "Catchpoint $any_nb, PROGRAM_ERROR at $any_addr in foo \\\(\\\).*at .*foo.adb:$any_nb"
> +  "Catchpoint $any_nb, PROGRAM_ERROR (\\\(foo.adb:$decimal explicit raise\\\) )?at $any_addr in foo \\\(\\\).*at .*foo.adb:$any_nb"
>  gdb_test "continue" \
>           "Continuing\.$eol$catchpoint_msg$eol.*SPOT2" \
>           "continuing to Program_Error exception"
> @@ -157,7 +157,7 @@ gdb_test "tcatch exception" \
>           "Temporary catchpoint $any_nb: all Ada exceptions"
>  
>  set temp_catchpoint_msg \
> -  "Temporary catchpoint $any_nb, CONSTRAINT_ERROR at $any_addr in foo \\\(\\\).*at .*foo.adb:$any_nb"
> +  "Temporary catchpoint $any_nb, CONSTRAINT_ERROR (\\\(.*\\\) )?at $any_addr in foo \\\(\\\).*at .*foo.adb:$any_nb"
>  gdb_test "continue" \
>           "Continuing\.$eol$temp_catchpoint_msg$eol.*SPOT1" \
>           "continuing to temporary catchpoint"
> diff --git a/gdb/testsuite/gdb.ada/mi_catch_ex.exp b/gdb/testsuite/gdb.ada/mi_catch_ex.exp
> index c9dd616..2ca3b6c 100644
> --- a/gdb/testsuite/gdb.ada/mi_catch_ex.exp
> +++ b/gdb/testsuite/gdb.ada/mi_catch_ex.exp
> @@ -80,7 +80,7 @@ mi_gdb_test "-catch-exception" \
>  
>  # Continue to caught exception.
>  
> -proc continue_to_exception { exception_name test } {
> +proc continue_to_exception { exception_name exception_message test } {
>      global hex any_nb
>  
>      mi_send_resuming_command "exec-continue" "$test"
> @@ -97,18 +97,18 @@ proc continue_to_exception { exception_name test } {
>  
>      # Now MI stream output.
>      mi_expect_stop \
> -	"breakpoint-hit\",disp=\"keep\",bkptno=\"$any_nb\",exception-name=\"$exception_name" \
> +	"breakpoint-hit\",disp=\"keep\",bkptno=\"$any_nb\",exception-name=\"$exception_name(\",exception-message=\"$exception_message)?" \
>  	"foo" "" ".*" ".*" \
>  	".*" \
>  	$test
>  }
>  
>  continue_to_exception \
> -    "CONSTRAINT_ERROR" \
> +    "CONSTRAINT_ERROR" "foo\\.adb:$decimal explicit raise" \
>      "continue until CE caught by all-exceptions catchpoint"
>  
>  continue_to_exception \
> -    "PROGRAM_ERROR" \
> +    "PROGRAM_ERROR" "foo\\.adb:$decimal explicit raise" \
>      "continue until PE caught by all-exceptions catchpoint"
>  
>  ################################################
> @@ -143,7 +143,7 @@ mi_gdb_test "-catch-exception -u" \
>              "catch unhandled exceptions"
>  
>  mi_execute_to "exec-continue" \
> -              "breakpoint-hit\",disp=\"keep\",bkptno=\"$any_nb\",exception-name=\"PROGRAM_ERROR" \
> +              "breakpoint-hit\",disp=\"keep\",bkptno=\"$any_nb\",exception-name=\"PROGRAM_ERROR(\",exception-message=\"foo\\.adb:$decimal explicit raise)?" \
>                "foo" "" ".*" ".*" \
>                ".*" \
>                "continue to exception catchpoint hit"
> diff --git a/gdb/testsuite/gdb.ada/mi_ex_cond.exp b/gdb/testsuite/gdb.ada/mi_ex_cond.exp
> index 78765be..369f155 100644
> --- a/gdb/testsuite/gdb.ada/mi_ex_cond.exp
> +++ b/gdb/testsuite/gdb.ada/mi_ex_cond.exp
> @@ -81,7 +81,7 @@ mi_gdb_test "-catch-exception -c \"i = 2\" -e constraint_error" \
>  mi_run_cmd
>  
>  mi_expect_stop \
> -    "breakpoint-hit\",disp=\"keep\",bkptno=\"$any_nb\",exception-name=\"CONSTRAINT_ERROR" \
> +    "breakpoint-hit\",disp=\"keep\",bkptno=\"$any_nb\",exception-name=\"CONSTRAINT_ERROR(\",exception-message=\"foo\\.adb:$decimal explicit raise)?" \
>      "foo" "" ".*" ".*" \
>      ".*" \
>      "run to exception catchpoint hit"
> -- 
> 2.1.4

-- 
Joel